RESUMO
RATIONALE: Vascular permeability is a hallmark of acute respiratory distress syndrome (ARDS) and ventilator-induced lung injury pathobiology; however, the mechanisms underlying this vascular dysregulation remain unclear, thereby impairing the development of desperately needed effective therapeutics. We have shown that sphingosine-1-phosphate (S1P) and 2-amino-2-(2-[4-octylphenyl]ethyl)-1,3-propanediol (FTY720) analogues are useful tools for exploring vascular barrier regulation mechanisms. OBJECTIVE: To experimentally define the effects of FTY720 regioisomers on lung endothelial cell barrier regulation. METHODS: Specific barrier-regulatory receptor and kinase inhibitors were utilized to probe signaling mechanisms involved in FTY720 regioisomer-mediated human lung endothelial cell barrier responses (trans-endothelial electrical resistance, TER). Docking simulations with the S1P1 receptor were performed to further evaluate FTY720 regioisomer signaling. RESULTS: FTY720 regioisomers produced potent endothelial cell barrier disruption reflected by declines in TER alterations. Pharmacologic inhibition of Gi-coupled S1P receptors (S1P1, S1P2, S1P3) failed to alter FTY720 regioisomer-mediated barrier disruption; findings that were corroborated by docking simulations demonstrating FTY720 regiosomers were repelled from S1P1 docking, in contrast to strong S1P1 binding elicited by S1P. Inhibition of either the barrier-disrupting PAR-1 receptor, the VEGF receptor, Rho-kinase, MAPK, NFkB, or PI3K failed to alter FTY720 regioisomer-induced endothelial cell barrier disruption. While FTY720 regioisomers significantly increased protein phosphatase 2 (PP2A) activity, PP2A inhibitors failed to alter FTY720 regioisomer-induced endothelial cell barrier disruption. CONCLUSIONS: Together, these results imply a vexing model of pulmonary vascular barrier dysregulation in response to FTY720-related compounds and highlight the need for further insights into mechanisms of vascular integrity required to promote the development of novel therapeutic tools to prevent or reverse the pulmonary vascular leak central to ARDS outcomes.
RESUMO
The platelet-derived growth factor receptor ß (PDGFR-ß) signaling pathway is a validated and important target for the treatment of certain malignant and nonmalignant pathologies. We previously identified a G-quadruplex-forming nuclease hypersensitive element (NHE) in the human PDGFR-ß promoter that putatively forms four overlapping G-quadruplexes. Therefore, we further investigated the structures and biological roles of the G-quadruplexes and i-motifs in the PDGFR-ß NHE with the ultimate goal of demonstrating an alternate and effective strategy for molecularly targeting the PDGFR-ß pathway. Significantly, we show that the primary G-quadruplex receptor for repression of PDGFR-ß is the 3'-end G-quadruplex, which has a GGA sequence at the 3'-end. Mutation studies using luciferase reporter plasmids highlight a novel set of G-quadruplex point mutations, some of which seem to provide conflicting results on effects on gene expression, prompting further investigation into the effect of these mutations on the i-motif-forming strand. Herein we characterize the formation of an equilibrium between at least two different i-motifs from the cytosine-rich (C-rich) sequence of the PDGFR-ß NHE. The apparently conflicting mutation results can be rationalized if we take into account the single base point mutation made in a critical cytosine run in the PDGFR-ß NHE that dramatically affects the equilibrium of i-motifs formed from this sequence. We identified a group of ellipticines that targets the G-quadruplexes in the PDGFR-ß promoter, and from this series of compounds, we selected the ellipticine analog GSA1129, which selectively targets the 3'-end G-quadruplex, to shift the dynamic equilibrium in the full-length sequence to favor this structure. We also identified a benzothiophene-2-carboxamide (NSC309874) as a PDGFR-ß i-motif-interactive compound. In vitro, GSA1129 and NSC309874 downregulate PDGFR-ß promoter activity and transcript in the neuroblastoma cell line SK-N-SH at subcytotoxic cell concentrations. GSA1129 also inhibits PDGFR-ß-driven cell proliferation and migration. With an established preclinical murine model of acute lung injury, we demonstrate that GSA1129 attenuates endotoxin-mediated acute lung inflammation. Our studies underscore the importance of considering the effects of point mutations on structure formation from the G- and C-rich sequences and provide further evidence for the involvement of both strands and associated structures in the control of gene expression.
Assuntos
Motivos de Aminoácidos , Desoxirribonucleases/química , Sistemas de Liberação de Medicamentos , Quadruplex G , Receptor beta de Fator de Crescimento Derivado de Plaquetas/química , Sequência de Bases , Regulação para Baixo , Quadruplex G/efeitos dos fármacos , Redes Reguladoras de Genes , Humanos , Mutação , Regiões Promotoras GenéticasRESUMO
Protein Kinase C (PKC) plays a significant role in thrombin-induced loss of endothelial cell (EC) barrier integrity; however, the existence of more than 10 isozymes of PKC and tissue-specific isoform expression has limited our understanding of this important second messenger in vascular homeostasis. In this study, we show that PKCδ isoform promotes thrombin-induced loss of human pulmonary artery EC barrier integrity, findings substantiated by PKCδ inhibitory studies (rottlerin), dominant negative PKCδ construct and PKCδ silencing (siRNA). In addition, we identified PKCδ as a signaling mediator upstream of both thrombin-induced MLC phosphorylation and Rho GTPase activation affecting stress fiber formation, cell contraction and loss of EC barrier integrity. Our inhibitor-based studies indicate that thrombin-induced PKCδ activation exerts a positive feedback on Rho GTPase activation and contributes to Rac1 GTPase inhibition. Moreover, PKD (or PKCµ) and CPI-17, two known PKCδ targets, were found to be activated by PKCδ in EC and served as modulators of cytoskeleton rearrangement. These studies clarify the role of PKCδ in EC cytoskeleton regulation, and highlight PKCδ as a therapeutic target in inflammatory lung disorders, characterized by the loss of barrier integrity, such as acute lung injury and sepsis.
Assuntos
Células Endoteliais/patologia , Pulmão/enzimologia , Pulmão/patologia , Proteína Quinase C-delta/metabolismo , Trombina/farmacologia , Acetofenonas/farmacologia , Benzopiranos/farmacologia , Ativação Enzimática/efeitos dos fármacos , Inativação Gênica/efeitos dos fármacos , Humanos , Peptídeos e Proteínas de Sinalização Intracelular , Modelos Biológicos , Proteínas Musculares , Cadeias Leves de Miosina/metabolismo , Fosfoproteínas Fosfatases , Fosforilação/efeitos dos fármacos , Proteína Quinase C , Proteína Quinase C-delta/antagonistas & inibidores , Transdução de Sinais/efeitos dos fármacos , Fibras de Estresse/efeitos dos fármacos , Fibras de Estresse/metabolismo , Proteínas rho de Ligação ao GTP/metabolismoRESUMO
Effective therapeutic agents are lacking for the prevention and reversal of vascular leak, a frequent pathophysiologic result of inflammatory processes such as acute respiratory distress syndrome (ARDS) and sepsis. We previously demonstrated the potent barrier-enhancing effects of related compounds sphingosine 1-phosphate (S1P), the pharmaceutical agent FTY720, and its analog (S)-FTY720 phosphonate (Tys) in models of inflammatory lung injury. In this study, we characterize additional novel FTY720 analogs for their potential to reduce vascular leak as well as utilize them as tools to better understand the mechanisms by which this class of agents modulates permeability. Transendothelial resistance (TER) and labeled dextran studies demonstrate that (R)-methoxy-FTY720 ((R)-OMe-FTY), (R)/(S)-fluoro-FTY720 (FTY-F), and ß-glucuronide-FTY720 (FTY-G) compounds display in vitro barrier-enhancing properties comparable or superior to FTY720 and S1P. In contrast, the (S)-methoxy-FTY720 ((S)-OMe-FTY) analog disrupts lung endothelial cell (EC) barrier integrity in TER studies in association with actin stress fiber formation and robust intracellular calcium release, but independent of myosin light chain or ERK phosphorylation. Additional mechanistic studies with (R)-OMe-FTY, FTY-F, and FTY-G suggest that lung EC barrier enhancement is mediated through lipid raft signaling, Gi-linked receptor coupling to downstream tyrosine phosphorylation events, and S1PR1-dependent receptor ligation. These results provide important mechanistic insights into modulation of pulmonary vascular barrier function by FTY720-related compounds and highlight common signaling events that may assist the development of novel therapeutic tools in the prevention or reversal of the pulmonary vascular leak that characterizes ARDS.
Assuntos
Células Endoteliais/citologia , Células Endoteliais/efeitos dos fármacos , Cloridrato de Fingolimode/análogos & derivados , Cloridrato de Fingolimode/farmacologia , Artéria Pulmonar/citologia , Artéria Pulmonar/efeitos dos fármacos , Células Cultivadas , Células Endoteliais/metabolismo , Cloridrato de Fingolimode/química , Humanos , Permeabilidade/efeitos dos fármacos , Artéria Pulmonar/metabolismo , Relação Estrutura-AtividadeRESUMO
Ventilator-induced inflammatory lung injury (VILI) is mechanistically linked to increased NAMPT transcription and circulating levels of nicotinamide phosphoribosyl-transferase (NAMPT/PBEF). Although VILI severity is attenuated by reduced NAMPT/PBEF bioavailability, the precise contribution of NAMPT/PBEF and excessive mechanical stress to VILI pathobiology is unknown. We now report that NAMPT/PBEF induces lung NFκB transcriptional activities and inflammatory injury via direct ligation of Toll-like receptor 4 (TLR4). Computational analysis demonstrated that NAMPT/PBEF and MD-2, a TLR4-binding protein essential for LPS-induced TLR4 activation, share ~30% sequence identity and exhibit striking structural similarity in loop regions critical for MD-2-TLR4 binding. Unlike MD-2, whose TLR4 binding alone is insufficient to initiate TLR4 signaling, NAMPT/PBEF alone produces robust TLR4 activation, likely via a protruding region of NAMPT/PBEF (S402-N412) with structural similarity to LPS. The identification of this unique mode of TLR4 activation by NAMPT/PBEF advances the understanding of innate immunity responses as well as the untoward events associated with mechanical stress-induced lung inflammation.
Assuntos
Citocinas/química , Citocinas/imunologia , NF-kappa B/imunologia , Nicotinamida Fosforribosiltransferase/química , Nicotinamida Fosforribosiltransferase/imunologia , Receptor 4 Toll-Like/química , Receptor 4 Toll-Like/imunologia , Lesão Pulmonar Induzida por Ventilação Mecânica/imunologia , Animais , Sítios de Ligação , Células Cultivadas , Humanos , Camundongos , Camundongos Endogâmicos C57BL , Camundongos Knockout , Modelos Químicos , Simulação de Acoplamento Molecular , Pneumonia/imunologia , Ligação Proteica , Conformação ProteicaRESUMO
Effective therapeutic agents are lacking for the prevention and reversal of vascular leak, a frequent pathophysiologic result of inflammatory processes such as acute respiratory distress syndrome (ARDS) and sepsis. We previously demonstrated the potent barrier-enhancing effects of related compounds sphingosine 1-phosphate (S1P), the pharmaceutical agent FTY720, and its analog (S)-FTY720 phosphonate (Tys) in models of inflammatory lung injury. In this study, we characterize additional novel FTY720 analogs for their potential to reduce vascular leak as well as utilize them as tools to better understand the mechanisms by which this class of agents modulates permeability. Transendothelial resistance (TER) and labeled dextran studies demonstrate that (R)-methoxy-FTY720 ((R)-OMe-FTY), (R)/(S)-fluoro-FTY720 (FTY-F), and ß-glucuronide-FTY720 (FTY-G) compounds display in vitro barrier-enhancing properties comparable or superior to FTY720 and S1P. In contrast, the (S)-methoxy-FTY720 ((S)-OMe-FTY) analog disrupts lung endothelial cell (EC) barrier integrity in TER studies in association with actin stress fiber formation and robust intracellular calcium release, but independent of myosin light chain or ERK phosphorylation. Additional mechanistic studies with (R)-OMe-FTY, FTY-F, and FTY-G suggest that lung EC barrier enhancement is mediated through lipid raft signaling, Gi-linked receptor coupling to downstream tyrosine phosphorylation events, and S1PR1-dependent receptor ligation. These results provide important mechanistic insights into modulation of pulmonary vascular barrier function by FTY720-related compounds and highlight common signaling events that may assist the development of novel therapeutic tools in the prevention or reversal of the pulmonary vascular leak that characterizes ARDS.
Assuntos
Cloridrato de Fingolimode/análogos & derivados , Cálcio/metabolismo , Linhagem Celular , Células Endoteliais/citologia , Células Endoteliais/efeitos dos fármacos , Células Endoteliais/metabolismo , MAP Quinases Reguladas por Sinal Extracelular/metabolismo , Cloridrato de Fingolimode/farmacologia , Fluoretos/química , Glucuronídeos/química , Humanos , Lisofosfolipídeos/metabolismo , Microscopia de Fluorescência , Permeabilidade/efeitos dos fármacos , Fosforilação , Artéria Pulmonar/citologia , Transdução de Sinais/efeitos dos fármacos , Esfingosina/análogos & derivados , Esfingosina/metabolismoRESUMO
Increased nicotinamide phosphoribosyltransferase (NAMPT) transcription is mechanistically linked to ventilator-induced inflammatory lung injury (VILI), with VILI severity attenuated by reduced NAMPT bioavailability. The molecular mechanisms of NAMPT promoter regulation in response to excessive mechanical stress remain poorly understood. The objective of this study was to define the contribution of specific transcription factors, acute respiratory distress syndrome (ARDS)-associated single nucleotide polymorphisms (SNPs), and promoter demethylation to NAMPT transcriptional regulation in response to mechanical stress. In vivo NAMPT protein expression levels were examined in mice exposed to high tidal volume mechanical ventilation. In vitro NAMPT expression levels were examined in human pulmonary artery endothelial cells exposed to 5 or 18% cyclic stretch (CS), with NAMPT promoter activity assessed using NAMPT promoter luciferase reporter constructs with a series of nested deletions. In vitro NAMPT transcriptional regulation was further characterized by measuring luciferase activity, DNA demethylation, and chromatin immunoprecipitation. VILI-challenged mice exhibited significantly increased NAMPT expression in bronchoalveolar lavage leukocytes and in lung endothelium. A mechanical stress-inducible region (MSIR) was identified in the NAMPT promoter from -2,428 to -2,128 bp. This MSIR regulates NAMPT promoter activity, mRNA expression, and signal transducer and activator of transcription 5 (STAT5) binding, which is significantly increased by 18% CS. In addition, NAMPT promoter activity was increased by pharmacologic promoter demethylation and inhibited by STAT5 silencing. ARDS-associated NAMPT promoter SNPs rs59744560 (-948G/T) and rs7789066 (-2,422A/G) each significantly elevated NAMPT promoter activity in response to 18% CS in a STAT5-dependent manner. Our results show that NAMPT is a key novel ARDS therapeutic target and candidate gene with genetic/epigenetic transcriptional regulation in response to excessive mechanical stress.
Assuntos
Citocinas/genética , Células Endoteliais/fisiologia , Nicotinamida Fosforribosiltransferase/genética , Síndrome do Desconforto Respiratório/genética , Fator de Transcrição STAT5/metabolismo , Proteínas Supressoras de Tumor/metabolismo , Regiões 5' não Traduzidas/genética , Lesão Pulmonar Aguda/etiologia , Lesão Pulmonar Aguda/genética , Lesão Pulmonar Aguda/metabolismo , Animais , Células Cultivadas , Citocinas/fisiologia , Metilação de DNA/fisiologia , Modelos Animais de Doenças , Células Endoteliais/citologia , Epigênese Genética/genética , Regulação da Expressão Gênica/fisiologia , Variação Genética/genética , Humanos , Masculino , Camundongos Endogâmicos C57BL , Nicotinamida Fosforribosiltransferase/fisiologia , Regiões Promotoras Genéticas/fisiologia , Artéria Pulmonar/citologia , RNA Interferente Pequeno/genética , Respiração Artificial/efeitos adversos , Síndrome do Desconforto Respiratório/etiologia , Síndrome do Desconforto Respiratório/metabolismo , Estresse MecânicoRESUMO
The inflamed lung exhibits oxidative and nitrative modifications of multiple target proteins, potentially reflecting disease severity and progression. We identified sphingosine-1-phosphate receptor-3 (S1PR3), a critical signaling molecule mediating cell proliferation and vascular permeability, as a nitrated plasma protein in mice with acute lung injury (ALI). We explored S1PR3 as a potential biomarker in murine and human ALI. In vivo nitrated and total S1PR3 concentrations were determined by immunoprecipitation and microarray studies in mice, and by ELISA in human plasma. In vitro nitrated S1PR3 concentrations were evaluated in human lung vascular endothelial cells (ECs) or within microparticles shed from ECs after exposure to barrier-disrupting agonists (LPS, low-molecular-weight hyaluronan, and thrombin). The effects of S1PR3-containing microparticles on EC barrier function were assessed by transendothelial electrical resistance (TER). Nitrated S1PR3 was identified in the plasma of murine ALI and in humans with severe sepsis-induced ALI. Elevated total S1PR3 plasma concentrations (> 251 pg/ml) were linked to sepsis and ALI mortality. In vitro EC exposure to barrier-disrupting agents induced S1PR3 nitration and the shedding of S1PR3-containing microparticles, which significantly reduced TER, consistent with increased permeability. These changes were attenuated by reduced S1PR3 expression (small interfering RNAs). These results suggest that microparticles containing nitrated S1PR3 shed into the circulation during inflammatory lung states, and represent a novel ALI biomarker linked to disease severity and outcome.
Assuntos
Lesão Pulmonar Aguda/sangue , Receptores de Lisoesfingolipídeo/sangue , Lesão Pulmonar Aguda/imunologia , Lesão Pulmonar Aguda/mortalidade , Adulto , Idoso , Animais , Biomarcadores/sangue , Permeabilidade Capilar , Estudos de Casos e Controles , Micropartículas Derivadas de Células/metabolismo , Células Cultivadas , Impedância Elétrica , Células Endoteliais/imunologia , Células Endoteliais/metabolismo , Células Endoteliais/patologia , Endotélio Vascular/patologia , Feminino , Técnicas de Silenciamento de Genes , Humanos , Estimativa de Kaplan-Meier , Lipopolissacarídeos/farmacologia , Pulmão/patologia , Masculino , Camundongos , Pessoa de Meia-Idade , Artéria Pulmonar/patologia , Interferência de RNA , Receptores de Lisoesfingolipídeo/genética , Receptores de Esfingosina-1-Fosfato , Tirosina/análogos & derivados , Tirosina/sangue , Lesão Pulmonar Induzida por Ventilação Mecânica/metabolismoRESUMO
Acute lung injury (ALI) results from loss of alveolar-capillary barrier integrity and the evolution of high-permeability pulmonary edema resulting in alveolar flooding and significant morbidity and mortality. HMGB1 is a late mediator of sepsis which uniquely participates in the evolution of sepsis and sepsis-induced ALI. The molecular events by which HMGB1 contributes to ALI remain poorly characterized. We characterized the role of HMGB1 in endothelial cell (EC) cytoskeletal rearrangement and vascular permeability, events essential to paracellular gap formation and barrier dysfunction characteristic of ALI. Initial experiments demonstrated HMGB1-mediated dose-dependent (5-20 µg/ml) decreases in transendothelial cell electrical resistance (TER) in the human pulmonary artery EC, a reflection of loss of barrier integrity. Furthermore, HMGB1 produced dose-dependent increases in paracellular gap formation in concert with loss of peripheral organized actin fibers, dissociation of cell-cell junctional cadherins, and the development of central stress fibers, a phenotypic change associated with increased contractile activity and increased EC permeability. Using siRNA strategies directed against known HMGB1 receptors (RAGE, TLR2, TLR4), we systematically determined that the receptor for advanced glycation end products (RAGE) is the primary receptor signaling HMGB1-induced TER decreases and paracellular gap formation via p38 MAP kinase activation and phosphorylation of the actin-binding protein, Hsp27. These studies add to the understanding of HMGB1-induced inflammatory events and vascular barrier disruption and offer the potential for clinical intervention in sepsis-induced ALI.
Assuntos
Permeabilidade Capilar/efeitos dos fármacos , Citoesqueleto/efeitos dos fármacos , Células Endoteliais/efeitos dos fármacos , Proteína HMGB1/farmacologia , Artéria Pulmonar/citologia , Citoesqueleto de Actina/efeitos dos fármacos , Citoesqueleto de Actina/metabolismo , Actinas/metabolismo , Antígenos CD/metabolismo , Caderinas/metabolismo , Permeabilidade Capilar/fisiologia , Células Cultivadas , Citoesqueleto/metabolismo , Impedância Elétrica , Células Endoteliais/citologia , Células Endoteliais/fisiologia , Junções Comunicantes/efeitos dos fármacos , Proteína HMGB1/genética , Proteínas de Choque Térmico HSP27/metabolismo , Proteínas de Choque Térmico , Humanos , Peptídeos e Proteínas de Sinalização Intracelular/genética , Peptídeos e Proteínas de Sinalização Intracelular/metabolismo , Modelos Biológicos , Chaperonas Moleculares , Fosforilação/efeitos dos fármacos , Inibidores de Proteínas Quinases/farmacologia , Proteínas Serina-Treonina Quinases/genética , Proteínas Serina-Treonina Quinases/metabolismo , RNA Interferente Pequeno/genética , Receptor para Produtos Finais de Glicação Avançada/genética , Receptor para Produtos Finais de Glicação Avançada/metabolismo , Proteínas Recombinantes/genética , Proteínas Recombinantes/farmacologia , Transdução de Sinais/efeitos dos fármacos , Transdução de Sinais/fisiologia , Fibras de Estresse/efeitos dos fármacos , Fibras de Estresse/metabolismo , Proteínas Quinases p38 Ativadas por Mitógeno/antagonistas & inibidores , Proteínas Quinases p38 Ativadas por Mitógeno/genética , Proteínas Quinases p38 Ativadas por Mitógeno/metabolismoRESUMO
Acute lung injury (ALI) and mechanical ventilator-induced lung injury (VILI), major causes of acute respiratory failure with elevated morbidity and mortality, are characterized by significant pulmonary inflammation and alveolar/vascular barrier dysfunction. Previous studies highlighted the role of the non-muscle myosin light chain kinase isoform (nmMLCK) as an essential element of the inflammatory response, with variants in the MYLK gene that contribute to ALI susceptibility. To define nmMLCK involvement further in acute inflammatory syndromes, we used two murine models of inflammatory lung injury, induced by either an intratracheal administration of lipopolysaccharide (LPS model) or mechanical ventilation with increased tidal volumes (the VILI model). Intravenous delivery of the membrane-permeant MLC kinase peptide inhibitor, PIK, produced a dose-dependent attenuation of both LPS-induced lung inflammation and VILI (~50% reductions in alveolar/vascular permeability and leukocyte influx). Intravenous injections of nmMLCK silencing RNA, either directly or as cargo within angiotensin-converting enzyme (ACE) antibody-conjugated liposomes (to target the pulmonary vasculature selectively), decreased nmMLCK lung expression (â¼70% reduction) and significantly attenuated LPS-induced and VILI-induced lung inflammation (â¼40% reduction in bronchoalveolar lavage protein). Compared with wild-type mice, nmMLCK knockout mice were significantly protected from VILI, with significant reductions in VILI-induced gene expression in biological pathways such as nrf2-mediated oxidative stress, coagulation, p53-signaling, leukocyte extravasation, and IL-6-signaling. These studies validate nmMLCK as an attractive target for ameliorating the adverse effects of dysregulated lung inflammation.
Assuntos
Lesão Pulmonar Aguda/prevenção & controle , Terapia Genética/métodos , Pulmão/efeitos dos fármacos , Quinase de Cadeia Leve de Miosina/antagonistas & inibidores , Inibidores de Proteínas Quinases/farmacologia , Interferência de RNA , Lesão Pulmonar Induzida por Ventilação Mecânica/prevenção & controle , Lesão Pulmonar Aguda/induzido quimicamente , Lesão Pulmonar Aguda/enzimologia , Lesão Pulmonar Aguda/genética , Lesão Pulmonar Aguda/imunologia , Animais , Anticorpos , Líquido da Lavagem Broncoalveolar/imunologia , Permeabilidade Capilar/efeitos dos fármacos , Células Cultivadas , Modelos Animais de Doenças , Humanos , Mediadores da Inflamação/metabolismo , Injeções Intravenosas , Lipopolissacarídeos , Lipossomos , Pulmão/irrigação sanguínea , Pulmão/enzimologia , Pulmão/imunologia , Masculino , Camundongos , Camundongos Endogâmicos C57BL , Camundongos Knockout , Cadeias Leves de Miosina/metabolismo , Quinase de Cadeia Leve de Miosina/deficiência , Quinase de Cadeia Leve de Miosina/genética , Quinase de Cadeia Leve de Miosina/metabolismo , Peptidil Dipeptidase A/imunologia , Fosforilação , Inibidores de Proteínas Quinases/administração & dosagem , RNA Interferente Pequeno/administração & dosagem , Transdução de Sinais/genética , Fatores de Tempo , Lesão Pulmonar Induzida por Ventilação Mecânica/enzimologia , Lesão Pulmonar Induzida por Ventilação Mecânica/genética , Lesão Pulmonar Induzida por Ventilação Mecânica/imunologiaRESUMO
Nonmuscle myosin light chain kinase (nmMLCK), a multi-functional cytoskeletal protein critical to vascular homeostasis, is highly regulated by tyrosine phosphorylation. We identified multiple novel c-Abl-mediated nmMLCK phosphorylation sites by mass spectroscopy analysis (including Y231, Y464, Y556, Y846) and examined their influence on nmMLCK function and human lung endothelial cell (EC) barrier regulation. Tyrosine phosphorylation of nmMLCK increased kinase activity, reversed nmMLCK-mediated inhibition of Arp2/3-mediated actin polymerization, and enhanced binding to the critical actin-binding phosphotyrosine protein, cortactin. EC challenge with sphingosine 1-phosphate (S1P), a potent barrier-enhancing agonist, resulted in c-Abl and phosphorylated nmMLCK recruitment into caveolin-enriched microdomains, rapid increases in Abl kinase activity, and spatial targeting of c-Abl to barrier-promoting cortical actin structures. Conversely, reduced c-Abl expression in EC (siRNA) markedly attenuated S1P-mediated cortical actin formation, reduced the EC modulus of elasticity (assessed by atomic force microscopy), reduced nmMLCK and cortactin tyrosine phosphorylation, and attenuated S1P-mediated barrier enhancement. These studies indicate an essential role for Abl kinase in vascular barrier regulation via posttranslational modification of nmMLCK and strongly support c-Abl-cortactin-nmMLCK interaction as a novel determinant of cortical actin-based cytoskeletal rearrangement critical to S1P-mediated EC barrier enhancement.
Assuntos
Células Endoteliais/metabolismo , Quinase de Cadeia Leve de Miosina/metabolismo , Proteínas Proto-Oncogênicas c-abl/metabolismo , Tirosina/metabolismo , Actinas/metabolismo , Sequência de Aminoácidos , Sítios de Ligação/genética , Western Blotting , Permeabilidade Capilar/efeitos dos fármacos , Caveolinas/metabolismo , Linhagem Celular , Citoesqueleto/efeitos dos fármacos , Citoesqueleto/metabolismo , Células Endoteliais/citologia , Células Endoteliais/efeitos dos fármacos , Ativação Enzimática , Proteínas de Fluorescência Verde/genética , Proteínas de Fluorescência Verde/metabolismo , Humanos , Lisofosfolipídeos/farmacologia , Espectrometria de Massas , Microdomínios da Membrana/efeitos dos fármacos , Microdomínios da Membrana/metabolismo , Microscopia de Força Atômica , Microscopia Confocal , Dados de Sequência Molecular , Quinase de Cadeia Leve de Miosina/genética , Fosforilação , Ligação Proteica , Proteínas Proto-Oncogênicas c-abl/genética , Interferência de RNA , Esfingosina/análogos & derivados , Esfingosina/farmacologia , Tirosina/genéticaRESUMO
Epidemiologic studies have linked exposure to airborne pollutant particulate matter (PM) with increased cardiopulmonary mortality and morbidity. The mechanisms of PM-mediated lung pathophysiology, however, remain unknown. We tested the hypothesis that PM, via enhanced oxidative stress, disrupts lung endothelial cell (EC) barrier integrity, thereby enhancing organ dysfunction. Using PM collected from Ft. McHenry Tunnel (Baltimore, MD), we assessed PM-mediated changes in transendothelial electrical resistance (TER) (a highly sensitive measure of barrier function), reactive oxygen species (ROS) generation, and p38 mitogen-activated protein kinase (MAPK) activation in human pulmonary artery EC. PM induced significant dose (10-100 microg/ml)- and time (0-10 h)-dependent EC barrier disruption reflected by reduced TER values. Exposure of human lung EC to PM resulted in significant ROS generation, which was directly involved in PM-mediated EC barrier dysfunction, as N-acetyl-cysteine (NAC, 5 mM) pretreatment abolished both ROS production and barrier disruption induced by PM. Furthermore, PM induced p38 MAPK activation and HSP27 phosphorylation, events that were both attenuated by NAC. In addition, PM-induced EC barrier disruption was partially prevented by the p38 MAP kinase inhibitor SB203580 (10 microM) as well as by reduced expression of either p38 MAPK beta or HSP27 (siRNA). These results demonstrate that PM induces ROS generation in human lung endothelium, resulting in oxidative stress-mediated EC barrier disruption via p38 MAPK- and HSP27-dependent pathways. These findings support a novel mechanism for PM-induced lung dysfunction and adverse cardiopulmonary outcomes.
Assuntos
Poluentes Atmosféricos/efeitos adversos , Células Endoteliais/enzimologia , Pneumopatias/enzimologia , Material Particulado/efeitos adversos , Espécies Reativas de Oxigênio/metabolismo , Proteínas Quinases p38 Ativadas por Mitógeno/metabolismo , Acetilcisteína/farmacologia , Poluentes Atmosféricos/farmacologia , Antioxidantes/farmacologia , Células Cultivadas , Relação Dose-Resposta a Droga , Células Endoteliais/patologia , Ativação Enzimática/efeitos dos fármacos , Inibidores Enzimáticos/farmacologia , Regulação da Expressão Gênica/efeitos dos fármacos , Proteínas de Choque Térmico HSP27/metabolismo , Proteínas de Choque Térmico , Humanos , Imidazóis/farmacologia , Pulmão , Pneumopatias/etiologia , Chaperonas Moleculares , Estresse Oxidativo/efeitos dos fármacos , Material Particulado/farmacologia , Fosforilação/efeitos dos fármacos , Piridinas/farmacologia , Proteínas Quinases p38 Ativadas por Mitógeno/antagonistas & inibidoresRESUMO
The therapeutic options for ameliorating the profound vascular permeability, alveolar flooding, and organ dysfunction that accompanies acute inflammatory lung injury (ALI) remain limited. Extending our previous finding that the intravenous administration of the sphingolipid angiogenic factor, sphingosine 1-phosphate (S1P), attenuates inflammatory lung injury and vascular permeability via ligation of S1PR(1), we determine that a direct intratracheal or intravenous administration of S1P, or a selective S1P receptor (S1PR(1)) agonist (SEW-2871), produces highly concentration-dependent barrier-regulatory responses in the murine lung. The intratracheal or intravenous administration of S1P or SEW-2871 at < 0.3 mg/kg was protective against LPS-induced murine lung inflammation and permeability. However, intratracheal delivery of S1P at 0.5 mg/kg (for 2 h) resulted in significant alveolar-capillary barrier disruption (with a 42% increase in bronchoalveolar lavage protein), and produced rapid lethality when delivered at 2 mg/kg. Despite the greater selectivity for S1PR(1), intratracheally delivered SEW-2871 at 0.5 mg/kg also resulted in significant alveolar-capillary barrier disruption, but was not lethal at 2 mg/kg. Consistent with the S1PR(1) regulation of alveolar/vascular barrier function, wild-type mice pretreated with the S1PR(1) inverse agonist, SB-649146, or S1PR(1)(+/-) mice exhibited reduced S1P/SEW-2871-mediated barrier protection after challenge with LPS. In contrast, S1PR(2)(-/-) knockout mice as well as mice with reduced S1PR(3) expression (via silencing S1PR3-containing nanocarriers) were protected against LPS-induced barrier disruption compared with control mice. These studies underscore the potential therapeutic effects of highly selective S1PR(1) receptor agonists in reducing inflammatory lung injury, and highlight the critical role of the S1P delivery route, S1PR(1) agonist concentration, and S1PR(1) expression in target tissues.
Assuntos
Barreira Alveolocapilar/fisiopatologia , Pulmão/irrigação sanguínea , Pulmão/fisiopatologia , Receptores de Lisoesfingolipídeo/metabolismo , Lesão Pulmonar Aguda/fisiopatologia , Animais , Barreira Alveolocapilar/efeitos dos fármacos , Líquidos Corporais , Relação Dose-Resposta a Droga , Vias de Administração de Medicamentos , Agonismo Inverso de Drogas , Deleção de Genes , Inativação Gênica/efeitos dos fármacos , Lipopolissacarídeos/farmacologia , Pulmão/efeitos dos fármacos , Masculino , Camundongos , Camundongos Endogâmicos C57BL , Camundongos Knockout , Oxidiazóis/agonistas , Oxidiazóis/farmacologia , Receptores de Lisoesfingolipídeo/agonistas , Receptores de Lisoesfingolipídeo/antagonistas & inibidores , Tiofenos/agonistas , Tiofenos/farmacologiaRESUMO
Acute lung injury represents the result of multiple pathways initiated by local or systemic insults and is characterized by profound vascular permeability, pulmonary edema, and life-threatening respiratory failure. Permeability-reducing therapies are of potential clinical utility but are currently unavailable. We hypothesized that polyethylene glycol (PEG) compounds, inert and non-toxic polymers that serve as a surrogate mucin lining in intestinal epithelium, may attenuate agonist-mediated lung endothelial cell (EC) barrier dysfunction. High molecular weight PEG (PEG15-20) produced rapid, dose-dependent increases in transendothelial electrical resistance (TER) in human lung endothelium cultured on gold microelectrodes, reflecting increased paracellular integrity. The maximal effective concentration of 8% PEG induced a sustained 125% increase in TER (40 h), results similar to barrier-enhancing agonists such as sphingosine 1-phosphate (40% increase in TER). Maximal PEG barrier enhancement was achieved at 45-60 min and PEG effectively reversed both thrombin- and LPS-induced EC barrier dysfunction. Consistent with the increase in TER, immunofluorescent studies demonstrated that PEG produced significant cytoskeletal rearrangement with formation of well-defined cortical actin rings and lamellipodia containing the actin-binding proteins, cortactin and MLCK, known participants in cell-matrix and cell-cell junctional adhesion. Finally, PEG challenge induced rapid alterations in levels of MAP kinase and MLC phosphorylation. In summary, PEG joins a number of EC barrier-regulatory agents which rapidly activate barrier-enhancing signal transduction pathways which target the cytoskeleton and provides a potential therapeutic strategy in inflammatory lung injury.
Assuntos
Actinas/metabolismo , Células Endoteliais/efeitos dos fármacos , Pulmão/citologia , Pulmão/efeitos dos fármacos , Polietilenoglicóis/farmacologia , Lesão Pulmonar Aguda/tratamento farmacológico , Lesão Pulmonar Aguda/metabolismo , Lesão Pulmonar Aguda/patologia , Junções Aderentes/efeitos dos fármacos , Junções Aderentes/metabolismo , Sinalização do Cálcio/efeitos dos fármacos , Células Cultivadas , Citoesqueleto/efeitos dos fármacos , Citoesqueleto/metabolismo , Relação Dose-Resposta a Droga , Impedância Elétrica , Células Endoteliais/metabolismo , Humanos , Pulmão/irrigação sanguínea , Pulmão/metabolismo , Microscopia de Fluorescência , Microscopia de Vídeo , Peso Molecular , Polietilenoglicóis/administração & dosagem , Polietilenoglicóis/química , Transdução de Sinais/efeitos dos fármacos , Acetato de Tetradecanoilforbol/farmacologia , Trombina/farmacologiaRESUMO
RATIONALE: We previously demonstrated pre-B-cell colony enhancing factor (PBEF) as a biomarker in sepsis and sepsis-induced acute lung injury (ALI) with genetic variants conferring ALI susceptibility. OBJECTIVES: To explore mechanistic participation of PBEF in ALI and ventilator-induced lung injury (VILI). METHODS: Two models of VILI were utilized to explore the role of PBEF using either recombinant PBEF or PBEF(+/-) mice. MEASUREMENTS AND MAIN RESULTS: Initial in vitro studies demonstrated recombinant human PBEF (rhPBEF) as a direct rat neutrophil chemotactic factor with in vivo studies demonstrating marked increases in bronchoalveolar lavage (BAL) leukocytes (PMNs) after intratracheal injection in C57BL/6J mice. These changes were accompanied by increased BAL levels of PMN chemoattractants (KC and MIP-2) and modest increases in lung vascular and alveolar permeability. We next explored the potential synergism between rhPBEF challenge (intratracheal) and a model of limited VILI (4 h, 30 ml/kg tidal volume) and observed dramatic increases in BAL PMNs, BAL protein, and cytokine levels (IL-6, TNF-alpha, KC) compared with either challenge alone. Gene expression profiling identified induction of ALI- and VILI-associated gene modules (nuclear factor-kappaB, leukocyte extravasation, apoptosis, Toll receptor pathways). Heterozygous PBEF(+/-) mice were significantly protected (reduced BAL protein, BAL IL-6 levels, peak inspiratory pressures) when exposed to a model of severe VILI (4 h, 40 ml/kg tidal volume) and exhibited significantly reduced expression of VILI-associated gene expression modules. Finally, strategies to reduce PBEF availability (neutralizing antibody) resulted in significant protection from VILI. CONCLUSIONS: These studies implicate PBEF as a key inflammatory mediator intimately involved in both the development and severity of ventilator-induced ALI.
Assuntos
Citocinas/fisiologia , Nicotinamida Fosforribosiltransferase/fisiologia , Síndrome do Desconforto Respiratório/fisiopatologia , Ventiladores Mecânicos , Animais , Líquido da Lavagem Broncoalveolar , Quimiocina CXCL1/metabolismo , Quimiocina CXCL2/metabolismo , Quimiotaxia de Leucócito/fisiologia , Perfilação da Expressão Gênica , Interleucina-6/análise , Macrófagos Alveolares/metabolismo , Camundongos , Camundongos Endogâmicos C57BL , Camundongos Transgênicos , Análise de Sequência com Séries de Oligonucleotídeos , Síndrome do Desconforto Respiratório/etiologia , Transdução de Sinais/fisiologia , Fator de Necrose Tumoral alfa/metabolismo , Ventiladores Mecânicos/efeitos adversosRESUMO
Endothelial cell (EC) involvement in viral hemorrhagic fevers has been clearly established. However, virally activated mechanisms leading to endothelial activation and dysfunction are not well understood. Several different potential mechanisms such as direct viral infection, alterations in procoagulant/anticoagulant balance, and increased cytokine production have been suggested. We utilized a model of EC barrier dysfunction and vascular endothelial leakage to explore the effect of bluetongue virus (BTV), a hemorrhagic fever virus of ruminants, on human lung endothelial cell barrier properties. Infection of human lung EC with BTV induced a significant and dose-dependent decrease in trans-endothelial electrical resistance (TER). Furthermore, decreases in TER occurred in conjunction with cytoskeletal rearrangement, suggesting a direct mechanism for viral infection-mediated endothelial barrier disruption. Interestingly, double-stranded RNA (dsRNA) mimicked the effects of BTV on endothelial barrier properties. Both BTV- and dsRNA-induced endothelial barrier dysfunction was blocked by treatment with a pharmacological inhibitor of p38 MAPK. The induction of vascular permeability by dsRNA treatment or BTV infection was concomitent with induction of inflammatory cytokines. Taken together, our data suggest that the presence of dsRNA during viral infections and subsequent activation of p38 MAPK is a potential molecular pathway for viral induction of hemorrhagic fevers. Collectively, our data suggest that inhibition of p38 MAPK may be a possible therapeutic approach to alter viral-induced acute hemorrhagic diseases.
Assuntos
Vírus Bluetongue/patogenicidade , Permeabilidade Capilar/efeitos dos fármacos , Endotélio Vascular/virologia , RNA de Cadeia Dupla/farmacologia , Proteínas Quinases p38 Ativadas por Mitógeno/fisiologia , Células Cultivadas , Citocinas/genética , Citoesqueleto/metabolismo , Endotélio Vascular/patologia , Regulação da Expressão Gênica , Febres Hemorrágicas Virais/etiologia , Febres Hemorrágicas Virais/patologia , Humanos , Pulmão/patologia , Pulmão/virologiaRESUMO
Endothelial cell (EC) barrier dysfunction results in increased vascular permeability observed in inflammation, tumor angiogenesis, and atherosclerosis. The platelet-derived phospholipid sphingosine-1-phosphate (S1P) decreases EC permeability in vitro and in vivo and thus has obvious therapeutic potential. We examined S1P-mediated human pulmonary artery EC signaling and barrier regulation in caveolin-enriched microdomains (CEM). Immunoblotting from S1P-treated EC revealed S1P-mediated rapid recruitment (1 microM, 5 min) to CEMs of the S1P receptors S1P1 and S1P3, p110 PI3 kinase alpha and beta catalytic subunits, the Rac1 GEF, Tiam1, and alpha-actinin isoforms 1 and 4. Immunoprecipitated p110 PI3 kinase catalytic subunits from S1P-treated EC exhibited PIP3 production in CEMs. Immunoprecipitation of S1P receptors from CEM fractions revealed complexes containing Tiam1 and S1P1. PI3 kinase inhibition (LY294002) attenuated S1P-induced Tiam1 association with S1P1, Tiam1/Rac1 activation, alpha-actinin-1/4 recruitment, and EC barrier enhancement. Silencing of either S1P1 or Tiam1 expression resulted in the loss of S1P-mediated Rac1 activation and alpha-actinin-1/4 recruitment to CEM. Finally, silencing S1P1, Tiam1, or both alpha-actinin isoforms 1/4 inhibits S1P-induced cortical F-actin rearrangement and S1P-mediated barrier enhancement. Taken together, these results suggest that S1P-induced recruitment of S1P1 to CEM fractions promotes PI3 kinase-mediated Tiam1/Rac1 activation required for alpha-actinin-1/4-regulated cortical actin rearrangement and EC barrier enhancement.
Assuntos
Actinina/fisiologia , Endotélio Vascular/metabolismo , Regulação Enzimológica da Expressão Gênica , Fatores de Troca do Nucleotídeo Guanina/fisiologia , Proteínas de Neoplasias/fisiologia , Fosfatidilinositol 3-Quinases/fisiologia , Receptores de Lisoesfingolipídeo/fisiologia , Proteínas rac1 de Ligação ao GTP/fisiologia , Actinina/metabolismo , Domínio Catalítico , Caveolina 1/química , Células Cultivadas , Colesterol/química , Cromonas/farmacologia , Citoesqueleto/metabolismo , Eletroforese em Gel de Poliacrilamida , Endotélio Vascular/patologia , Inibidores Enzimáticos/farmacologia , Fatores de Troca do Nucleotídeo Guanina/metabolismo , Humanos , Immunoblotting , Imunoprecipitação , Inflamação , Proteínas dos Microfilamentos/metabolismo , Microscopia de Fluorescência , Modelos Biológicos , Morfolinas/farmacologia , Fosfatidilinositol 3-Quinases/metabolismo , Isoformas de Proteínas , Estrutura Terciária de Proteína , Artéria Pulmonar/patologia , RNA Interferente Pequeno/metabolismo , Transdução de Sinais , Proteína 1 Indutora de Invasão e Metástase de Linfoma de Células T , TransfecçãoRESUMO
Increased endothelial cell (EC) permeability is central to the pathophysiology of inflammatory syndromes such as sepsis and acute lung injury (ALI). Activated protein C (APC), a serine protease critically involved in the regulation of coagulation and inflammatory processes, improves sepsis survival through an unknown mechanism. We hypothesized a direct effect of APC to both prevent increased EC permeability and to restore vascular integrity after edemagenic agonists. We measured changes in transendothelial electrical resistance (TER) and observed that APC produced concentration-dependent attenuation of TER reductions evoked by thrombin. We next explored known EC barrier-protective signaling pathways and observed dose-dependent APC-mediated increases in cortical myosin light chain (MLC) phosphorylation in concert with cortically distributed actin polymerization, findings highly suggestive of Rac GTPase involvement. We next determined that APC directly increases Rac1 activity, with inhibition of Rac1 activity significantly attenuating APC-mediated barrier protection to thrombin challenge. Finally, as these signaling events were similar to those evoked by the potent EC barrier-enhancing agonist, sphingosine 1-phosphate (S1P), we explored potential cross-talk between endothelial protein C receptor (EPCR) and S1P1, the receptors for APC and S1P, respectively. EPCR-blocking antibody (RCR-252) significantly attenuated both APC-mediated barrier protection and increased MLC phosphorylation. We next observed rapid, EPCR and PI 3-kinase-dependent, APC-mediated phosphorylation of S1P1 on threonine residues consistent with S1P1 receptor activation. Co-immunoprecipitation studies demonstrate an interaction between EPCR and S1P1 upon APC treatment. Targeted silencing of S1P1 expression using siRNA significantly reduced APC-mediated barrier protection against thrombin. These data suggest that novel EPCR ligation and S1P1 transactivation results in EC cytoskeletal rearrangement and barrier protection, components potentially critical to the improved survival of APC-treated patients with severe sepsis.
Assuntos
Fatores de Coagulação Sanguínea/metabolismo , Endotélio/metabolismo , Pulmão/patologia , Proteína C/metabolismo , Receptores de Superfície Celular/metabolismo , Receptores de Lisoesfingolipídeo/metabolismo , Ativação Transcricional , Actinas/metabolismo , Fatores de Coagulação Sanguínea/química , Células Cultivadas , Citoesqueleto/metabolismo , Relação Dose-Resposta a Droga , Impedância Elétrica , Endotélio/patologia , Endotélio Vascular/metabolismo , Genes Dominantes , Humanos , Imunoprecipitação , Pulmão/metabolismo , Microscopia de Fluorescência , Modelos Biológicos , Cadeias Leves de Miosina/química , Fosforilação , Ligação Proteica , RNA Interferente Pequeno/metabolismo , Receptores de Superfície Celular/química , Sepse/metabolismo , Serina/química , Transdução de Sinais , Treonina/química , Trombina/metabolismo , Fatores de Tempo , Transfecção , Proteínas rac de Ligação ao GTP/metabolismo , Proteínas rac1 de Ligação ao GTP/metabolismoRESUMO
We recently reported the critical importance of Rac GTPase-dependent cortical actin rearrangement in the augmentation of pulmonary endothelial cell (EC) barrier function by sphingosine 1-phosphate (S1P). We now describe functional roles for the actin-binding proteins cortactin and EC myosin light chain kinase (MLCK) in mediating this response. Antisense down-regulation of cortactin protein expression significantly inhibits S1P-induced barrier enhancement in cultured human pulmonary artery EC as measured by transendothelial electrical resistance (TER). Immunofluorescence studies reveal rapid, Rac-dependent translocation of cortactin to the expanded cortical actin band following S1P challenge, where colocalization with EC MLCK occurs within 5 min. Adenoviral overexpression of a Rac dominant negative mutant attenuates TER elevation by S1P. S1P also induces a rapid increase in cortactin tyrosine phosphorylation (within 30 s) critical to subsequent barrier enhancement, since EC transfected with a tyrosine-deficient mutant cortactin exhibit a blunted TER response. Direct binding of EC MLCK to the cortactin Src homology 3 domain appears essential to S1P barrier regulation, since cortactin blocking peptide inhibits both S1P-induced MLC phosphorylation and peak S1P-induced TER values. These data support novel roles for the cytoskeletal proteins cortactin and EC MLCK in mediating lung vascular barrier augmentation evoked by S1P.
Assuntos
Células Endoteliais/metabolismo , Pulmão/citologia , Lisofosfolipídeos/metabolismo , Proteínas dos Microfilamentos/fisiologia , Quinase de Cadeia Leve de Miosina/metabolismo , Esfingosina/metabolismo , Actinas/metabolismo , Western Blotting , Células Cultivadas , Cortactina , Citoesqueleto/metabolismo , Regulação para Baixo , Endotélio Vascular/metabolismo , GTP Fosfo-Hidrolases/metabolismo , Genes Dominantes , Vetores Genéticos , Humanos , Proteínas dos Microfilamentos/metabolismo , Microscopia de Fluorescência , Oligonucleotídeos Antissenso/farmacologia , Peptídeos/química , Fosforilação , Testes de Precipitina , Ligação Proteica , Estrutura Terciária de Proteína , Transporte Proteico , Esfingosina/análogos & derivados , Fatores de Tempo , Transfecção , Tirosina/metabolismo , Domínios de Homologia de srcRESUMO
Direct protein kinase C (PKC) activation with phorbol myristate acetate (PMA) results in the loss of endothelial monolayer integrity in bovine lung endothelial cells (EC) but produces barrier enhancement in human lung endothelium. To extend these findings, we studied EC contractile events and observed a 40% increase in myosin light chain (MLC) phosphorylation in bovine endothelium following PMA challenge. The increase in PMA-mediated MLC phosphorylation occurred at sites distinct from Ser19/Thr18, sites catalyzed by MLC kinase (MLCK), and immunoblotting with antibodies specific to phosphorylated Ser19/Thr18 demonstrated profound time-dependent Ser19/Thr18 dephosphorylation. These events occurred in conjunction with rearrangement of stress fibers into a grid-like network, but without an increase in cellular contraction as measured by silicone membrane wrinkling assay. The PMA-induced MLC dephosphorylation was not due to kinase inhibition but, rather, correlated with rapid increases in myosin-associated phosphatase 1 (PPase 1) activity. These data suggest that PMA-mediated EC barrier regulation may involve dual mechanisms that alter MLC phosphorylation. The increase in bovine MLC phosphorylation likely occurs via direct PKC-dependent MLC phosphorylation in conjunction with decreases in Ser19/Thr18 phosphorylation catalyzed by MLCK due to PMA-induced increases in PPase 1 activity. Together, these events result in stress fiber destabilization and profound actin rearrangement in bovine endothelium, which may result in the physiological alterations observed in these models.