RESUMO
Inducing cell death by the sphingolipid ceramide is a potential anticancer strategy, but the underlying mechanisms remain poorly defined. In this study, triggering an accumulation of ceramide in acute myeloid leukemia (AML) cells by inhibition of sphingosine kinase induced an apoptotic integrated stress response (ISR) through protein kinase R-mediated activation of the master transcription factor ATF4. This effect led to transcription of the BH3-only protein Noxa and degradation of the prosurvival Mcl-1 protein on which AML cells are highly dependent for survival. Targeting this novel ISR pathway, in combination with the Bcl-2 inhibitor venetoclax, synergistically killed primary AML blasts, including those with venetoclax-resistant mutations, as well as immunophenotypic leukemic stem cells, and reduced leukemic engraftment in patient-derived AML xenografts. Collectively, these findings provide mechanistic insight into the anticancer effects of ceramide and preclinical evidence for new approaches to augment Bcl-2 inhibition in the therapy of AML and other cancers with high Mcl-1 dependency.
Assuntos
Antineoplásicos , Leucemia Mieloide Aguda , Antineoplásicos/uso terapêutico , Apoptose , Compostos Bicíclicos Heterocíclicos com Pontes/uso terapêutico , Linhagem Celular Tumoral , Ceramidas/farmacologia , Humanos , Leucemia Mieloide Aguda/tratamento farmacológico , Leucemia Mieloide Aguda/genética , Leucemia Mieloide Aguda/metabolismo , Proteína de Sequência 1 de Leucemia de Células Mieloides/metabolismo , Proteínas Proto-Oncogênicas c-bcl-2/metabolismoRESUMO
Calreticulin (CALR) is recurrently mutated in myelofibrosis via a frameshift that removes an endoplasmic reticulum retention signal, creating a neoepitope potentially targetable by immunotherapeutic approaches. We developed a specific rat monoclonal IgG2α antibody, 4D7, directed against the common sequence encoded by both insertion and deletion mutations. 4D7 selectively bound to cells co-expressing mutant CALR and thrombopoietin receptor (TpoR) and blocked JAK-STAT signalling, TPO-independent proliferation and megakaryocyte differentiation of mutant CALR myelofibrosis progenitors by disrupting the binding of CALR dimers to TpoR. Importantly, 4D7 inhibited proliferation of patient samples with both insertion and deletion CALR mutations but not JAK2 V617F and prolonged survival in xenografted bone marrow models of mutant CALR-dependent myeloproliferation. Together, our data demonstrate a novel therapeutic approach to target a problematic disease driven by a recurrent somatic mutation that would normally be considered undruggable.
Assuntos
Calreticulina , Transtornos Mieloproliferativos , Animais , Anticorpos Monoclonais , Calreticulina/genética , Calreticulina/metabolismo , Humanos , Janus Quinase 2/metabolismo , Mutação , Transtornos Mieloproliferativos/genética , Transtornos Mieloproliferativos/metabolismo , RatosRESUMO
Sphingosine 1-phosphate (S1P) is a signaling lipid that has broad roles, working either intracellularly through various protein targets, or extracellularly via a family of five G-protein coupled receptors. Agents that selectively and specifically target each of the S1P receptors have been sought as both biological tools and potential therapeutics. JTE-013, a small molecule antagonist of S1P receptors 2 and 4 (S1P2 and S1P4) has been widely used in defining the roles of these receptors in various biological processes. Indeed, our previous studies showed that JTE-013 had anti-acute myeloid leukaemia (AML) activity, supporting a role for S1P2 in the biology and therapeutic targeting of AML. Here we examined this further and describe lipidomic analysis of AML cells that revealed JTE-013 caused alterations in sphingolipid metabolism, increasing cellular ceramides, dihydroceramides, sphingosine and dihydrosphingosine. Further examination of the mechanisms behind these observations showed that JTE-013, at concentrations frequently used in the literature to target S1P2/4, inhibits several sphingolipid metabolic enzymes, including dihydroceramide desaturase 1 and both sphingosine kinases. Collectively, these findings demonstrate that JTE-013 can have broad off-target effects on sphingolipid metabolism and highlight that caution must be employed in interpreting the use of this reagent in defining the roles of S1P2/4.
Assuntos
Pirazóis/química , Piridinas/química , Esfingolipídeos/metabolismo , Receptores de Esfingosina-1-Fosfato/antagonistas & inibidores , Receptores de Esfingosina-1-Fosfato/metabolismo , Células HEK293 , Humanos , Cinética , Oxirredutases/química , Oxirredutases/genética , Oxirredutases/metabolismo , Pirazóis/farmacologia , Piridinas/farmacologia , Receptores de Esfingosina-1-Fosfato/genéticaRESUMO
Sphingosine kinase 1 (SK1) is a signalling enzyme that catalyses the phosphorylation of sphingosine to generate the bioactive lipid sphingosine 1-phosphate (S1P). A number of SK1 inhibitors and chemotherapeutics can induce the degradation of SK1, with the loss of this pro-survival enzyme shown to significantly contribute to the anti-cancer properties of these agents. Here we define the mechanistic basis for this degradation of SK1 in response to SK1 inhibitors, chemotherapeutics, and in natural protein turnover. Using an inducible SK1 expression system that enables the degradation of pre-formed SK1 to be assessed independent of transcriptional or translational effects, we found that SK1 was degraded primarily by the proteasome since several proteasome inhibitors blocked SK1 degradation, while lysosome, cathepsin B or pan caspase inhibitors had no effect. Importantly, we demonstrate that this proteasomal degradation of SK1 was enabled by its ubiquitination at Lys183 that appears facilitated by SK1 inhibitor-induced conformational changes in the structure of SK1 around this residue. Furthermore, using yeast two-hybrid screening, we identified Kelch-like protein 5 (KLHL5) as an important protein adaptor linking SK1 to the cullin 3 (Cul3) ubiquitin ligase complex. Notably, knockdown of KLHL5 or Cul3, use of a cullin inhibitor or a dominant-negative Cul3 all attenuated SK1 degradation. Collectively this data demonstrates the KLHL5/Cul3-based E3 ubiquitin ligase complex is important for regulation of SK1 protein stability via Lys183 ubiquitination, in response to SK1 inhibitors, chemotherapy and for normal SK1 protein turnover.
Assuntos
Proteínas de Transporte/metabolismo , Lisina/metabolismo , Proteínas dos Microfilamentos/metabolismo , Fosfotransferases (Aceptor do Grupo Álcool)/química , Fosfotransferases (Aceptor do Grupo Álcool)/metabolismo , Complexo de Endopeptidases do Proteassoma/metabolismo , Motivos de Aminoácidos , Proteínas de Transporte/genética , Proteínas Culina/genética , Proteínas Culina/metabolismo , Humanos , Lisina/genética , Proteínas dos Microfilamentos/genética , Fosfotransferases (Aceptor do Grupo Álcool)/genética , Complexo de Endopeptidases do Proteassoma/genética , Proteólise , UbiquitinaçãoRESUMO
While the two mammalian sphingosine kinases, SK1 and SK2, both catalyze the generation of pro-survival sphingosine 1-phosphate (S1P), their roles vary dependent on their different subcellular localization. SK1 is generally found in the cytoplasm or at the plasma membrane where it can promote cell proliferation and survival. SK2 can be present at the plasma membrane where it appears to have a similar function to SK1, but can also be localized to the nucleus, endoplasmic reticulum or mitochondria where it mediates cell death. Although SK2 has been implicated in cancer initiation and progression, the mechanisms regulating SK2 subcellular localization are undefined. Here, we report that SK2 interacts with the intermediate chain subunits of the retrograde-directed transport motor complex, cytoplasmic dynein 1 (DYNC1I1 and -2), and we show that this interaction, particularly with DYNC1I1, facilitates the transport of SK2 away from the plasma membrane. DYNC1I1 is dramatically downregulated in patient samples of glioblastoma (GBM), where lower expression of DYNC1I1 correlates with poorer patient survival. Notably, low DYNC1I1 expression in GBM cells coincided with more SK2 localized to the plasma membrane, where it has been recently implicated in oncogenesis. Re-expression of DYNC1I1 reduced plasma membrane-localized SK2 and extracellular S1P formation, and decreased GBM tumor growth and tumor-associated angiogenesis in vivo. Consistent with this, chemical inhibition of SK2 reduced the viability of patient-derived GBM cells in vitro and decreased GBM tumor growth in vivo. Thus, these findings demonstrate a tumor-suppressive function of DYNC1I1, and uncover new mechanistic insights into SK2 regulation which may have implications in targeting this enzyme as a therapeutic strategy in GBM.
Assuntos
Dineínas do Citoplasma/genética , Genes Supressores de Tumor , Glioblastoma/genética , Fosfotransferases (Aceptor do Grupo Álcool)/genética , Animais , Apoptose/genética , Carcinogênese/genética , Linhagem Celular Tumoral , Membrana Celular/genética , Proliferação de Células/genética , Regulação Neoplásica da Expressão Gênica , Glioblastoma/patologia , Células HEK293 , Humanos , Lisofosfolipídeos/genética , Camundongos , Esfingosina/análogos & derivados , Esfingosina/genética , Ensaios Antitumorais Modelo de XenoenxertoRESUMO
Sphingosine kinase 1 (SK1) is a key regulator of the cellular balance between proapoptotic and prosurvival sphingolipids. Oncogenic signaling by SK1 relies on its localization to the plasma membrane, which is mediated by the calcium and integrin binding protein CIB1 via its Ca2+-myristoyl switch function. Here we show that another member of the CIB family, CIB2, plays a surprisingly opposite role to CIB1 in the regulation of SK1 signaling. CIB2 bound SK1 on the same site as CIB1, yet it lacks the Ca2+-myristoyl switch function. As a result, CIB2 blocked translocation of SK1 to the plasma membrane and inhibited its subsequent signaling, which included sensitization to TNFα-induced apoptosis and inhibition of Ras-induced neoplastic transformation. CIB2 was significantly downregulated in ovarian cancer and low CIB2 expression was associated with poor prognosis in ovarian cancer patients. Notably, reintroduction of CIB2 in ovarian cancer cells blocked plasma membrane localization of endogenous SK1, reduced in vitro neoplastic growth and tumor growth in mice, and suppressed cell motility and invasiveness both in vitro and in vivo Consistent with the in vitro synergistic effects between the SK1-specific inhibitor SK1-I and standard chemotherapeutics, expression of CIB2 also sensitized ovarian cancer cells to carboplatin. Together, these findings identify CIB2 as a novel endogenous suppressor of SK1 signaling and potential prognostic marker and demonstrate the therapeutic potential of SK1 in this gynecologic malignancy. Cancer Res; 77(18); 4823-34. ©2017 AACR.
Assuntos
Biomarcadores Tumorais/metabolismo , Proteínas de Ligação ao Cálcio/metabolismo , Regulação Neoplásica da Expressão Gênica , Neoplasias Ovarianas/patologia , Fosfotransferases (Aceptor do Grupo Álcool)/metabolismo , Animais , Apoptose , Biomarcadores Tumorais/genética , Proteínas de Ligação ao Cálcio/genética , Movimento Celular , Proliferação de Células , Feminino , Humanos , Camundongos , Camundongos Endogâmicos NOD , Camundongos SCID , Invasividade Neoplásica , Estadiamento de Neoplasias , Neoplasias Ovarianas/genética , Neoplasias Ovarianas/metabolismo , Fosfotransferases (Aceptor do Grupo Álcool)/genética , Prognóstico , Células Tumorais Cultivadas , Ensaios Antitumorais Modelo de XenoenxertoRESUMO
The proteasome inhibitor bortezomib has proven to be invaluable in the treatment of myeloma. By exploiting the inherent high immunoglobulin protein production of malignant plasma cells, bortezomib induces endoplasmic reticulum (ER) stress and the unfolded protein response (UPR), resulting in myeloma cell death. In most cases, however, the disease remains incurable highlighting the need for new therapeutic targets. Sphingosine kinase 2 (SK2) has been proposed as one such therapeutic target for myeloma. Our observations that bortezomib and SK2 inhibitors independently elicited induction of ER stress and the UPR prompted us to examine potential synergy between these agents in myeloma. Targeting SK2 synergistically contributed to ER stress and UPR activation induced by bortezomib, as evidenced by activation of the IRE1 pathway and stress kinases JNK and p38MAPK, thereby resulting in potent synergistic myeloma apoptosis in vitro. The combination of bortezomib and SK2 inhibition also exhibited strong in vivo synergy and favourable effects on bone disease. Therefore, our studies suggest that perturbations of sphingolipid signalling can synergistically enhance the effects seen with proteasome inhibition, highlighting the potential for the combination of these two modes of increasing ER stress to be formally evaluated in clinical trials for the treatment of myeloma patients.
Assuntos
Antineoplásicos/farmacologia , Bortezomib/farmacologia , Estresse do Retículo Endoplasmático/efeitos dos fármacos , Mieloma Múltiplo/metabolismo , Fosfotransferases (Aceptor do Grupo Álcool)/antagonistas & inibidores , Animais , Apoptose/efeitos dos fármacos , Morte Celular/efeitos dos fármacos , Linhagem Celular Tumoral , Modelos Animais de Doenças , Relação Dose-Resposta a Droga , Sinergismo Farmacológico , Humanos , Modelos Biológicos , Terapia de Alvo Molecular , Mieloma Múltiplo/tratamento farmacológico , Mieloma Múltiplo/mortalidade , Mieloma Múltiplo/patologia , Inibidores de Proteassoma/farmacologia , Ensaios Antitumorais Modelo de XenoenxertoRESUMO
Acute myeloid leukemia (AML) is an aggressive malignancy where despite improvements in conventional chemotherapy and bone marrow transplantation, overall survival remains poor. Sphingosine kinase 1 (SPHK1) generates the bioactive lipid sphingosine 1-phosphate (S1P) and has established roles in tumor initiation, progression, and chemotherapy resistance in a wide range of cancers. The role and targeting of SPHK1 in primary AML, however, has not been previously investigated. Here we show that SPHK1 is overexpressed and constitutively activated in primary AML patient blasts but not in normal mononuclear cells. Subsequent targeting of SPHK1 induced caspase-dependent cell death in AML cell lines, primary AML patient blasts, and isolated AML patient leukemic progenitor/stem cells, with negligible effects on normal bone marrow CD34+ progenitors from healthy donors. Furthermore, administration of SPHK1 inhibitors to orthotopic AML patient-derived xenografts reduced tumor burden and prolonged overall survival without affecting murine hematopoiesis. SPHK1 inhibition was associated with reduced survival signaling from S1P receptor 2, resulting in selective downregulation of the prosurvival protein MCL1. Subsequent analysis showed that the combination of BH3 mimetics with either SPHK1 inhibition or S1P receptor 2 antagonism triggered synergistic AML cell death. These results support the notion that SPHK1 is a bona fide therapeutic target for the treatment of AML.
Assuntos
Regulação Leucêmica da Expressão Gênica , Leucemia Mieloide Aguda/tratamento farmacológico , Proteína de Sequência 1 de Leucemia de Células Mieloides/antagonistas & inibidores , Fosfotransferases (Aceptor do Grupo Álcool)/antagonistas & inibidores , Receptores de Lisoesfingolipídeo/antagonistas & inibidores , Clorometilcetonas de Aminoácidos/farmacologia , Amino Álcoois/farmacologia , Animais , Células da Medula Óssea/efeitos dos fármacos , Células da Medula Óssea/metabolismo , Células da Medula Óssea/patologia , Inibidores de Caspase/farmacologia , Caspases/genética , Caspases/metabolismo , Morte Celular/efeitos dos fármacos , Linhagem Celular Tumoral , Feminino , Humanos , Leucemia Mieloide Aguda/genética , Leucemia Mieloide Aguda/mortalidade , Leucemia Mieloide Aguda/patologia , Lisofosfolipídeos/metabolismo , Camundongos , Camundongos Endogâmicos NOD , Terapia de Alvo Molecular , Proteína de Sequência 1 de Leucemia de Células Mieloides/genética , Proteína de Sequência 1 de Leucemia de Células Mieloides/metabolismo , Células-Tronco Neoplásicas/efeitos dos fármacos , Células-Tronco Neoplásicas/metabolismo , Células-Tronco Neoplásicas/patologia , Fosfotransferases (Aceptor do Grupo Álcool)/genética , Fosfotransferases (Aceptor do Grupo Álcool)/metabolismo , Inibidores de Proteínas Quinases/farmacologia , Quinolinas/farmacologia , Receptores de Lisoesfingolipídeo/genética , Receptores de Lisoesfingolipídeo/metabolismo , Transdução de Sinais , Esfingosina/análogos & derivados , Esfingosina/metabolismo , Análise de Sobrevida , Ensaios Antitumorais Modelo de XenoenxertoRESUMO
While both human sphingosine kinases (SK1 and SK2) catalyze the generation of the pleiotropic signaling lipid sphingosine 1-phosphate, these enzymes appear to be functionally distinct. SK1 has well described roles in promoting cell survival, proliferation and neoplastic transformation. The roles of SK2, and its contribution to cancer, however, are much less clear. Some studies have suggested an anti-proliferative/pro-apoptotic function for SK2, while others indicate it has a pro-survival role and its inhibition can have anti-cancer effects. Our analysis of gene expression data revealed that SK2 is upregulated in many human cancers, but only to a small extent (up to 2.5-fold over normal tissue). Based on these findings, we examined the effect of different levels of cellular SK2 and showed that high-level overexpression reduced cell proliferation and survival, and increased cellular ceramide levels. In contrast, however, low-level SK2 overexpression promoted cell survival and proliferation, and induced neoplastic transformation in vivo. These findings coincided with decreased nuclear localization and increased plasma membrane localization of SK2, as well as increases in extracellular S1P formation. Hence, we have shown for the first time that SK2 can have a direct role in promoting oncogenesis, supporting the use of SK2-specific inhibitors as anti-cancer agents.
Assuntos
Membrana Celular/metabolismo , Núcleo Celular/metabolismo , Fosfotransferases (Aceptor do Grupo Álcool)/metabolismo , Apoptose , Carcinogênese , Proliferação de Células , Sobrevivência Celular , Ceramidas/metabolismo , Regulação Neoplásica da Expressão Gênica , Células HEK293 , Humanos , Lisofosfolipídeos/metabolismo , Fosfotransferases (Aceptor do Grupo Álcool)/genética , Transporte Proteico , Esfingosina/análogos & derivados , Esfingosina/metabolismoRESUMO
ROCK signaling causes epidermal hyper-proliferation by increasing ECM production, elevating dermal stiffness, and enhancing Fak-mediated mechano-transduction signaling. Elevated dermal stiffness in turn causes ROCK activation, establishing mechano-reciprocity, a positive feedback loop that can promote tumors. We have identified a negative feedback mechanism that limits excessive ROCK signaling during wound healing and is lost in squamous cell carcinomas (SCCs). Signal flux through ROCK was selectively tuned down by increased levels of 14-3-3ζ, which interacted with Mypt1, a ROCK signaling antagonist. In 14-3-3ζ(-/-) mice, unrestrained ROCK signaling at wound margins elevated ECM production and reduced ECM remodeling, increasing dermal stiffness and causing rapid wound healing. Conversely, 14-3-3ζ deficiency enhanced cutaneous SCC size. Significantly, inhibiting 14-3-3ζ with a novel pharmacological agent accelerated wound healing 2-fold. Patient samples of chronic non-healing wounds overexpressed 14-3-3ζ, while cutaneous SCCs had reduced 14-3-3ζ. These results reveal a novel 14-3-3ζ-dependent mechanism that negatively regulates mechano-reciprocity, suggesting new therapeutic opportunities.
Assuntos
Proteínas 14-3-3/metabolismo , Proliferação de Células/fisiologia , Homeostase/fisiologia , Transdução de Sinais/fisiologia , Cicatrização/fisiologia , Quinases Associadas a rho/metabolismo , Animais , Epiderme/metabolismo , CamundongosRESUMO
Sphingosine 1-phosphate (S1P) is a bioactive lipid that can function both extracellularly and intracellularly to mediate a variety of cellular processes. Using lipid affinity matrices and a radiolabeled lipid binding assay, we reveal that S1P directly interacts with the transcription factor peroxisome proliferator-activated receptor (PPAR)γ. Herein, we show that S1P treatment of human endothelial cells (ECs) activated a luciferase-tagged PPARγ-specific gene reporter by â¼12-fold, independent of the S1P receptors. More specifically, in silico docking, gene reporter, and binding assays revealed that His323 of the PPARγ ligand binding domain is important for binding to S1P. PPARγ functions when associated with coregulatory proteins, and herein we identify that peroxisome proliferator-activated receptor-γ coactivator 1 (PGC1)ß binds to PPARγ in ECs and their progenitors (nonadherent endothelial forming cells) and that the formation of this PPARγ:PGC1ß complex is increased in response to S1P. ECs treated with S1P selectively regulated known PPARγ target genes with PGC1ß and plasminogen-activated inhibitor-1 being increased, no change to adipocyte fatty acid binding protein 2 and suppression of CD36. S1P-induced in vitro tube formation was significantly attenuated in the presence of the PPARγ antagonist GW9662, and in vivo application of GW9662 also reduced vascular development in Matrigel plugs. Interestingly, activation of PPARγ by the synthetic ligand troglitazone also reduced tube formation in vitro and in vivo. To support this, Sphk1(-/-)Sphk2(+/-) mice, with low circulating S1P levels, demonstrated a similar reduction in vascular development. Taken together, our data reveal that the transcription factor, PPARγ, is a bona fide intracellular target for S1P and thus suggest that the S1P:PPARγ:PGC1ß complex may be a useful target to manipulate neovascularization.
Assuntos
Células Endoteliais da Veia Umbilical Humana/metabolismo , Lisofosfolipídeos/metabolismo , Neovascularização Fisiológica/fisiologia , PPAR gama/metabolismo , Receptores de Lisoesfingolipídeo/metabolismo , Esfingosina/análogos & derivados , Animais , Antígenos CD36/genética , Antígenos CD36/metabolismo , Proteínas de Transporte/genética , Proteínas de Transporte/metabolismo , Células HEK293 , Células Endoteliais da Veia Umbilical Humana/citologia , Humanos , Lisofosfolipídeos/genética , Camundongos , Camundongos Knockout , PPAR gama/genética , Coativador 1-alfa do Receptor gama Ativado por Proliferador de Peroxissomo , Fosfotransferases (Aceptor do Grupo Álcool)/genética , Fosfotransferases (Aceptor do Grupo Álcool)/metabolismo , Inibidor 1 de Ativador de Plasminogênio/genética , Inibidor 1 de Ativador de Plasminogênio/metabolismo , Proteínas de Ligação a RNA , Receptores de Lisoesfingolipídeo/genética , Serpina E2/genética , Serpina E2/metabolismo , Esfingosina/genética , Esfingosina/metabolismo , Fatores de Transcrição/genética , Fatores de Transcrição/metabolismo , Células U937RESUMO
The dynamic balance of cellular sphingolipids, the sphingolipid rheostat, is an important determinant of cell fate, and is commonly deregulated in cancer. Sphingosine 1-phosphate is a signaling molecule with anti-apoptotic, pro-proliferative and pro-angiogenic effects, while conversely, ceramide and sphingosine are pro-apoptotic. The sphingosine kinases (SKs) are key regulators of this sphingolipid rheostat, and are attractive targets for anti-cancer therapy. Here we report a first-in-class ATP-binding site-directed small molecule SK inhibitor, MP-A08, discovered using an approach of structural homology modelling of the ATP-binding site of SK1 and in silico docking with small molecule libraries. MP-A08 is a highly selective ATP competitive SK inhibitor that targets both SK1 and SK2. MP-A08 blocks pro-proliferative signalling pathways, induces mitochondrial-associated apoptosis in a SK-dependent manner, and reduces the growth of human lung adenocarcinoma tumours in a mouse xenograft model by both inducing tumour cell apoptosis and inhibiting tumour angiogenesis. Thus, this selective ATP competitive SK inhibitor provides a promising candidate for potential development as an anti-cancer therapy, and also, due to its different mode of inhibition to other known SK inhibitors, both validates the SKs as targets for anti-cancer therapy, and represents an important experimental tool to study these enzymes.
Assuntos
Adenocarcinoma/tratamento farmacológico , Trifosfato de Adenosina/química , Antineoplásicos/química , Inibidores Enzimáticos/química , Neoplasias Pulmonares/tratamento farmacológico , Fosfotransferases (Aceptor do Grupo Álcool)/antagonistas & inibidores , Adenocarcinoma/metabolismo , Animais , Apoptose , Sítios de Ligação , Linhagem Celular , Linhagem Celular Tumoral , Feminino , Células HEK293 , Humanos , Neoplasias Pulmonares/metabolismo , Células MCF-7 , Masculino , Camundongos , Camundongos Transgênicos , Conformação Molecular , Mutagênese , Mutação , Transplante de Neoplasias , Neovascularização Patológica , Ligação Proteica , Esfingolipídeos/químicaRESUMO
OBJECTIVES: The use of endothelial progenitor cells in vascular therapies has been limited due to their low numbers present in the bone marrow and peripheral blood. The aim of this study was to investigate the effect of sphingosine kinase on the de-differentiation of mature human endothelial cells toward a progenitor phenotype. METHODS: The lipid enzyme sphingosine kinase-1 was lentivirally over-expressed in human umbilical vein endothelial cells and cells were analyzed for progenitor phenotype and function. RESULTS: Sphingosine kinase-1 mRNA expression was induced approximately 150-fold with a resultant 20-fold increase in sphingosine kinase-1 enzymatic activity. The mRNA expression of the progenitor cell markers CD34, CD133, and CD117 and transcription factor NANOG increased, while the endothelial cell markers analyzed were largely unchanged. The protein level of mature endothelial cell surface markers CD31, CD144, and von Willebrand factor significantly decreased compared to controls. In addition, functional assays provided further evidence for a de-differentiated phenotype with increased viability, reduced uptake of acetylated low-density lipoprotein and decreased tube formation in Matrigel in the cells over-expressing sphingosine kinase-1. CONCLUSIONS: These findings suggest that over-expression of sphingosine kinase-1 in human endothelial cells promotes, in part, their de-differentiation to a progenitor cell phenotype, and is thus a potential tool for the generation of a large population of vascular progenitor cells for therapeutic use.
Assuntos
Desdiferenciação Celular , Células Endoteliais/enzimologia , Regulação Enzimológica da Expressão Gênica , Fosfotransferases (Aceptor do Grupo Álcool)/biossíntese , Células-Tronco/enzimologia , Antígenos de Diferenciação/biossíntese , Antígenos de Diferenciação/genética , Células Endoteliais/citologia , Células HEK293 , Humanos , Lentivirus , Fosfotransferases (Aceptor do Grupo Álcool)/genética , Células-Tronco/citologia , Transdução GenéticaRESUMO
Sphingosine kinase 1 (SK1) is an important regulator of cellular signalling that has gained recent attention as a potential target for anti-cancer therapies. SK1 activity, subcellular localization and oncogenic function are regulated by phosphorylation and dephosphorylation at Ser225. ERK1/2 have been identified as the protein kinases responsible for phosphorylation and activation of SK1. Conversely, dephosphorylation and deactivation of SK1 occurs by protein phosphatase 2A (PP2A). Active PP2A, however, is a heterotrimer, composed of tightly associated catalytic and structural subunits that can interact with an array of regulatory subunits, which are critical for determining holoenzyme substrate specificity and subcellular localization. Thus, PP2A represents a large family of holoenzyme complexes with different activities and diverse substrate specificities. To date the regulatory subunit essential for targeting PP2A to SK1 has remained undefined. Here, we demonstrate a critical role for the B'α (B56α/PR61α/PPP2R5A) regulatory subunit of PP2A in SK1 dephosphorylation. B'α was found to interact with the c-terminus of SK1, and reduce SK1 phosphorylation when overexpressed, while having no effect on upstream ERK1/2 activation. siRNA-mediated knockdown of B'α increased SK1 phosphorylation, activity and membrane localization of endogenous SK1. Furthermore, overexpression of B'α blocked agonist-induced translocation of SK1 to the plasma membrane and abrogated SK1-induced neoplastic transformation of NIH3T3 fibroblasts. Thus, the PP2A-B'α holoenzyme appears to function as an important endogenous regulator of SK1.
Assuntos
Membrana Celular/enzimologia , Fosfotransferases (Aceptor do Grupo Álcool)/metabolismo , Proteína Fosfatase 2/metabolismo , Animais , Transformação Celular Neoplásica , Técnicas de Silenciamento de Genes , Células HEK293 , Humanos , Imunoprecipitação , Camundongos , Células NIH 3T3 , Fosforilação , Ligação Proteica , Transporte ProteicoRESUMO
SK1 (sphingosine kinase 1) plays an important role in many aspects of cellular regulation. Most notably, elevated cellular SK1 activity leads to increased cell proliferation, protection from apoptosis, and induction of neoplastic transformation. We have previously shown that translocation of SK1 from the cytoplasm to the plasma membrane is integral for oncogenesis mediated by this enzyme. The molecular mechanism mediating this translocation of SK1 has remained undefined. Here, we demonstrate a direct role for CIB1 (calcium and integrin-binding protein 1) in this process. We show that CIB1 interacts with SK1 in a Ca(2+)-dependent manner at the previously identified "calmodulin-binding site" of SK1. We also demonstrate that CIB1 functions as a Ca(2+)-myristoyl switch, providing a mechanism whereby it translocates SK1 to the plasma membrane. Both small interfering RNA knockdown of CIB1 and the use of a dominant-negative CIB1 we have generated prevent the agonist-dependent translocation of SK1. Furthermore, we demonstrate the requirement of CIB1-mediated translocation of SK1 in controlling cellular sphingosine 1-phosphate generation and associated anti-apoptotic signaling.
Assuntos
Proteínas de Ligação ao Cálcio/metabolismo , Membrana Celular/enzimologia , Fosfotransferases (Aceptor do Grupo Álcool)/metabolismo , Apoptose/efeitos dos fármacos , Sítios de Ligação , Cálcio/metabolismo , Calmodulina/metabolismo , Linhagem Celular Tumoral , Membrana Celular/efeitos dos fármacos , Técnicas de Silenciamento de Genes , Genes Dominantes/genética , Humanos , Ácido Mirístico/metabolismo , NF-kappa B/metabolismo , Ligação Proteica/efeitos dos fármacos , Transporte Proteico/efeitos dos fármacos , Fator de Necrose Tumoral alfa/farmacologiaRESUMO
Sphingosine kinase 1 (SK1) catalyses the generation of sphingosine 1-phosphate (S1P), a bioactive phospholipid that influences a diverse range of cellular processes, including proliferation, survival, adhesion, migration, morphogenesis and differentiation. SK1 is controlled by various mechanisms, including transcriptional regulation, and post-translational activation by phosphorylation and protein-protein interactions which can regulate both the activity and localisation of this enzyme. To gain a better understanding of the regulatory mechanisms controlling SK1 activity and function we performed a yeast two-hybrid screen to identify SK1-interacting proteins. Using this approach we identified that SK1 interacts with subunit 7 (eta) of cytosolic chaperonin CCT (chaperonin containing t-complex polypeptide, also called TRiC for TCP-1 ring complex), a hexadecameric chaperonin that binds unfolded polypeptides and mediates their folding and release in an ATP-dependent manner. Further analysis of the SK1-CCTeta interaction demonstrated that other CCT/TRiC subunits also associated with SK1 in HEK293T cell lysates in an ATP-sensitive manner, suggesting that the intact, functional, multimeric CCT/TRiC complex associated with SK1. Furthermore, pulse-chase studies indicated that CCT/TRiC binds specifically to newly translated SK1. Finally, depletion of functional CCT/TRiC through the use of RNA interference in HeLa cells or temperature sensitive CCT yeast mutants reduced cellular SK1 activity. Thus, combined this data suggests that SK1 is a CCT/TRiC substrate, and that this chaperonin facilitates folding of newly translated SK1 into its mature active form.
Assuntos
Chaperoninas/metabolismo , Fosfotransferases (Aceptor do Grupo Álcool)/metabolismo , Chaperonina com TCP-1 , Fibroblastos/metabolismo , Células HeLa , Humanos , Leucócitos/metabolismo , Lisofosfolipídeos/metabolismo , Fosfotransferases (Aceptor do Grupo Álcool)/biossíntese , Fosfotransferases (Aceptor do Grupo Álcool)/genética , Conformação Proteica , Dobramento de Proteína , Saccharomyces cerevisiae/genética , Saccharomyces cerevisiae/metabolismo , Esfingosina/análogos & derivados , Esfingosina/metabolismo , Ativação Transcricional , Transfecção , Técnicas do Sistema de Duplo-HíbridoRESUMO
Sphingosine kinase 1 (SK1) is an important regulator of cellular signaling that has been implicated in a broad range of cellular processes. Cell exposure to a wide array of growth factors, cytokines, and other cell agonists can result in a rapid and transient increase in SK activity via an activating phosphorylation. We have previously identified extracellular signal-regulated kinases 1 and 2 (ERK1/2) as the kinases responsible for the phosphorylation of human SK1 at Ser(225), but the corresponding phosphatase targeting this phosphorylation has remained undefined. Here, we provide data to support a role for protein phosphatase 2A (PP2A) in the deactivation of SK1 through dephosphorylation of phospho-Ser(225). The catalytic subunit of PP2A (PP2Ac) was found to interact with SK1 using both GST-pulldown and coimmunoprecipitation analyses. Coexpression of PP2Ac with SK1 resulted in reduced Ser(225) phosphorylation of SK1 in human embryonic kidney (HEK293) cells. In vitro phosphatase assays showed that PP2Ac dephosphorylated both recombinant SK1 and a phosphopeptide based on the phospho-Ser(225) region of SK1. Finally, both basal and tumor necrosis factor-alpha-stimulated cellular SK1 activity were regulated by molecular manipulation of PP2Ac activity. Thus, PP2A appears to function as an endogenous regulator of SK1 phosphorylation.
Assuntos
Fosfotransferases (Aceptor do Grupo Álcool)/metabolismo , Proteína Fosfatase 2/metabolismo , Animais , Ativação Enzimática , MAP Quinases Reguladas por Sinal Extracelular/metabolismo , Inativação Gênica , Glutationa Transferase/metabolismo , Humanos , Músculo Esquelético/enzimologia , Fosforilação , Fosfotransferases (Aceptor do Grupo Álcool)/química , Proteína Fosfatase 2/química , Estrutura Terciária de Proteína , Coelhos , Serina/química , Frações Subcelulares/metabolismo , Fator de Necrose Tumoral alfa/metabolismoRESUMO
Tetracycline-regulated expression systems have been widely used for inducible protein expression in cultured mammalian cells. With these systems, however, leakiness in expression of the target gene in the absence of the inducing agent is a frequent problem. Here we describe a novel approach to overcome this problem that involves the incorporation of AU-rich mRNA destabilizing elements (AREs) into the 3' untranslated regions of the tetracycline-inducible constructs. Using the inducible expression of sphingosine kinase 1 and 2 in HEK293 cells as model systems, we found this ARE approach to be remarkably successful in ablating expression of these proteins in the absence of doxycycline through decreasing stability of their mRNAs. We show that this undemanding and flexible process results in a substantial decrease in the leakiness of the tetracycline-inducible expression system while maintaining a high level of target protein expression following induction.
Assuntos
Doxiciclina/farmacologia , Regulação da Expressão Gênica/efeitos dos fármacos , Fosfotransferases (Aceptor do Grupo Álcool)/genética , RNA Mensageiro/metabolismo , Regiões 3' não Traduzidas/fisiologia , Sequência de Bases , Células Cultivadas , Humanos , Dados de Sequência Molecular , Estabilidade de RNARESUMO
Sphingosine 1-phosphate (S1P) has many important roles in mammalian cells, including contributing to the control of cell survival and proliferation. S1P is generated by sphingosine kinases (SKs), of which two mammalian isoforms have been identified (SK1 and SK2). To gain a better understanding of SK regulation, we have used a yeast two-hybrid screen to identify SK1-interacting proteins and established elongation factor 1A (eEF1A) as one such protein that associates with both SK1 and SK2. We show the direct interaction of eEF1A with the SKs in vitro, whereas the physiological relevance of this association was demonstrated by co-immunoprecipitation of the endogenous proteins from cell lysates. Although the canonical role of eEF1A resides in protein synthesis, it has also been implicated in other roles, including regulating the activity of some signaling enzymes. Thus, we examined the potential role of eEF1A in regulation of the SKs and show that eEF1A is able to directly increase the activity of SK1 and SK2 approximately 3-fold in vitro. Substrate kinetics demonstrated that eEF1A increased the catalytic rate of both SKs, while having no observable effect on substrate affinities of these enzymes for either ATP or sphingosine. Overexpression of eEF1A in quiescent Chinese hamster ovary cells increased cellular SK activity, whereas a small interfering RNA-mediated decrease in eEF1A levels in MCF7 cells substantially reduced cellular SK activity and S1P levels, supporting the in vivo physiological relevance of this interaction. Thus, this study has established a novel mechanism of regulation of both SK1 and SK2 that is mediated by their interaction with eEF1A.
Assuntos
Lisofosfolipídeos/metabolismo , Fator 1 de Elongação de Peptídeos/metabolismo , Fosfotransferases (Aceptor do Grupo Álcool)/metabolismo , Transdução de Sinais/fisiologia , Esfingosina/análogos & derivados , Animais , Células CHO , Catálise , Proliferação de Células , Sobrevivência Celular/fisiologia , Cricetinae , Cricetulus , Ativação Enzimática/fisiologia , Humanos , Isoenzimas/genética , Isoenzimas/metabolismo , Lisofosfolipídeos/genética , Fator 1 de Elongação de Peptídeos/antagonistas & inibidores , Fator 1 de Elongação de Peptídeos/genética , Fosfotransferases (Aceptor do Grupo Álcool)/genética , Ligação Proteica/fisiologia , RNA Interferente Pequeno/genética , Esfingosina/genética , Esfingosina/metabolismoRESUMO
Sphingosine kinases catalyze the formation of sphingosine 1-phosphate, a bioactive lipid involved in many aspects of cellular regulation, including the fundamental biological processes of cell growth and survival. A diverse range of cell agonists induce activation of human sphingosine kinase 1 (hSK1) and, commonly, its translocation to the plasma membrane. Although the activation of hSK1 in response to at least some agonists occurs directly via its phosphorylation at Ser225 by ERK1/2, many aspects governing the regulation of this phosphorylation and subsequent translocation remain unknown. Here, in an attempt to understand some of these processes, we have examined the known interaction of hSK1 with calmodulin (CaM). By using a combination of limited proteolysis, peptide interaction analysis, and site-directed mutagenesis, we have identified that the CaM-binding site of hSK1 resides in the region spanned by residues 191-206. Specifically, Phe197 and Leu198 are critically involved in the interaction because a version of hSK1 incorporating mutations of both Phe197 --> Ala and Leu198 --> Gln failed to bind CaM. We have also shown for the first time that human sphingosine kinase 2 (hSK2) binds CaM, and does so via a CaM binding region that is conserved with hSK1 because comparable mutations in hSK2 also ablate CaM binding to this protein. By using the CaM-binding-deficient version of hSK1, we have begun to elucidate the role of CaM in hSK1 regulation by demonstrating that disruption of the CaM-binding site ablates agonist-induced translocation of hSK1 from the cytoplasm to the plasma membrane, while having no effect on hSK1 phosphorylation and catalytic activation.