Loss of mitogen-activated protein kinase phosphate-5 aggravates islet dysfunction in mice with type 1 and type 2 diabetes.

Impaired functionality and loss of islet ß-cells are the primary abnormalities underlying the pathogenesis of both type 1 and 2 diabetes (T1DM and T2DM). However, specific therapeutic and preventive mechanisms underlying these conditions remain unclear. Mitogen-activated protein kinase phosphatase-5 (MKP-5) has been implicated in carcinogenesis, lipid metabolism regulation, and immune cell activation. In a previous study, we demonstrated the involvement of exogenous MKP-5 in the regulation of obesity-induced T2DM. However, the role of endogenous MKP-5 in the T1DM and T2DM processes is unclear. Thus, mice with MKP-5 knockout (KO) were generated and used to establish mouse models of both T1DM and T2DM. Our results showed that MKP-5 KO exacerbated diabetes-related symptoms in mice with both T1DM and T2DM. Given that most phenotypic studies on islet dysfunction have focused on mice with T2DM rather than T1DM, we specifically aimed to investigate the role of endoplasmic reticulum stress (ERS) and autophagy in T2DM KO islets. To accomplish this, we performed RNA sequence analysis to gain comprehensive insight into the molecular mechanisms associated with ERS and autophagy in T2DM KO islets. The results showed that the islets from mice with MKP-5 KO triggered 5' adenosine monophosphate-activated protein kinase (AMPK)-mediated autophagy inhibition and glucose-regulated protein 78 (GRP-78)-dominated ERS. Hence, we concluded that the autophagy impairment, resulting in islet dysfunction in mice with MKP-5 KO, is mediated through GRP-78 involvement. These findings provide valuable insights into the molecular pathogenesis of diabetes and highlight the significant role of MKP-5. Moreover, this knowledge holds promise for novel therapeutic strategies targeting MKP-5 for diabetes management.

Retinoic Acid-Induced Regulation of Inflammatory Pathways Is a Potential Sepsis Treatment.

Sepsis is among the most dangerous known diseases, resulting from the dysregulation of the innate immune system in a process that is characterized largely by proinflammatory cytokines. It manifests as an excessive immune response to a pathogen and often leads to life-threatening complications such as shock and multiple-organ failure. Within the past several decades, much progress has been made to better understand the pathophysiology of sepsis and improve treatment. However, the average case-fatality rate for sepsis remains high. Current anti-inflammatory therapeutics for sepsis are not effective for use as first-line treatments. Focusing on all-trans-retinoic acid (RA), or activated vitamin A, as a novel anti-inflammatory agent, we have shown both in vitro and in vivo that RA decreases the production of proinflammatory cytokines. In vitro studies using mouse RAW 264.7 macrophages show that RA decreases tumor necrosis factor alpha (TNF-α) and interleukin-1ß (IL-1ß) and increases mitogen-activated protein kinase phosphatase 1 (MKP-1). RA treatment was also associated with the reduced phosphorylation of key inflammatory signaling proteins. Using a lipopolysaccharide and cecal slurry sepsis model, we found that RA significantly reduced mortality rates in mice, downregulated proinflammatory cytokine production, decreased neutrophil infiltration into lung tissue, and reduced the destructive lung histopathology typically seen in sepsis. We propose that RA may increase the function of native regulatory pathways and serve as a novel treatment for sepsis.

Enhanced MAPK1 Function Causes a Neurodevelopmental Disorder within the RASopathy Clinical Spectrum.

Signal transduction through the RAF-MEK-ERK pathway, the first described mitogen-associated protein kinase (MAPK) cascade, mediates multiple cellular processes and participates in early and late developmental programs. Aberrant signaling through this cascade contributes to oncogenesis and underlies the RASopathies, a family of cancer-prone disorders. Here, we report that de novo missense variants in MAPK1, encoding the mitogen-activated protein kinase 1 (i.e., extracellular signal-regulated protein kinase 2, ERK2), cause a neurodevelopmental disease within the RASopathy phenotypic spectrum, reminiscent of Noonan syndrome in some subjects. Pathogenic variants promote increased phosphorylation of the kinase, which enhances translocation to the nucleus and boosts MAPK signaling in vitro and in vivo. Two variant classes are identified, one of which directly disrupts binding to MKP3, a dual-specificity protein phosphatase negatively regulating ERK function. Importantly, signal dysregulation driven by pathogenic MAPK1 variants is stimulus reliant and retains dependence on MEK activity. Our data support a model in which the identified pathogenic variants operate with counteracting effects on MAPK1 function by differentially impacting the ability of the kinase to interact with regulators and substrates, which likely explains the minor role of these variants as driver events contributing to oncogenesis. After nearly 20 years from the discovery of the first gene implicated in Noonan syndrome, PTPN11, the last tier of the MAPK cascade joins the group of genes mutated in RASopathies.

Low let-7d microRNA levels in chick embryos enhance innate immunity against Mycoplasma gallisepticum by suppressing the mitogen-activated protein kinase pathway.

Chick embryos are a valuable model for studying immunity and vaccines. Therefore, it is crucial to investigate the molecular mechanism of the Mycoplasma gallisepticum (MG)-induced immune response in chick embryos for the prevention and control of MG. In this study, we screened for downregulated let-7d microRNA in MG-infected chicken embryonic lungs to explore its involvement in the innate immune mechanism against MG. Here, we demonstrated that low levels of let-7d are a protective mechanism for chicken embryo primary type II pneumocytes (CP-II) in the presence of MG. Specifically, we found that depressed levels of let-7 in CP-II cells reduced the adhesion capacity of MG. This suppressive effect was achieved through the activated mitogen-activated protein kinase phosphatase 1 (MKP1) target gene and the inactivated mitogen-activated protein kinase (MAPK) pathway. Furthermore, MG-induced hyperinflammation and cell death were both alleviated by downregulation of let-7d. In conclusion, chick embryos protect themselves against MG infection through the innate immune molecule let-7d, which may result from its function as an inhibitor of the MAPK pathway to effectively mitigate MG adhesion, the inflammatory response and cell apoptosis. This study may provide new insight into the development of vaccines against MG.

Acute Endoplasmic Reticulum Stress Suppresses Hepatic Gluconeogenesis by Stimulating MAPK Phosphatase 3 Degradation.

Drug-induced liver injury (DILI) is a widespread and harmful disease, and is closely linked to acute endoplasmic reticulum (ER) stress. Previous reports have shown that acute ER stress can suppress hepatic gluconeogenesis and even leads to hypoglycemia. However, the mechanism is still unclear. MAPK phosphatase 3 (MKP-3) is a positive regulator for gluconeogenesis. Thus, this study was conducted to investigate the role of MKP-3 in the suppression of gluconeogenesis by acute ER stress, as well as the regulatory role of acute ER stress on the expression of MKP-3. Results showed that acute ER stress induced by tunicamycin significantly suppressed gluconeogenesis in both hepatocytes and mouse liver, reduced glucose production level in hepatocytes, and decreased fasting blood glucose level in mice. Additionally, the protein level of MKP-3 was reduced by acute ER stress in both hepatocytes and mouse liver. Mkp-3 deficiency eliminated the inhibitory effect of acute ER stress on gluconeogenesis in hepatocytes. Moreover, the reduction effect of acute ER stress on blood glucose level and hepatic glucose 6-phosphatase (G6pc) expression was not observed in the liver-specific Mkp-3 knockout mice. Furthermore, activation of protein kinase R-like ER kinase (PERK) decreased the MKP-3 protein level, while inactivation of PERK abolished the reduction effect of acute ER stress on the MKP-3 protein level in hepatocytes. Taken together, our study suggested that acute ER stress could suppress hepatic gluconeogenesis by stimulating MKP-3 degradation via PERK, at least partially. Thus, MKP-3 might be a therapeutic target for DILI-related hypoglycemia.

MKP-1 Deficiency Exacerbates Skin Fibrosis in a Mouse Model of Scleroderma.

Scleroderma is a chronic fibrotic disease, where proinflammatory and profibrotic events precede collagen accumulation. MKP-1 [mitogen-activated protein kinase (MAPK) phosphatase-1] downregulates inflammatory MAPK pathways suppressing inflammation. MKP-1 also supports Th1 polarization, which could shift Th1/Th2 balance away from profibrotic Th2 profile prevalent in scleroderma. In the present study, we investigated the potential protective role of MKP-1 in scleroderma. We utilized bleomycin-induced dermal fibrosis model as a well-characterized experimental model of scleroderma. Dermal fibrosis and collagen deposition as well as the expression of inflammatory and profibrotic mediators were analyzed in the skin samples. Bleomycin-induced dermal thickness and lipodystrophy were increased in MKP-1-deficient mice. MKP-1 deficiency enhanced collagen accumulation and increased expression of collagens, 1A1 and 3A1, in the dermis. Bleomycin-treated skin from MKP-1-deficient mice also showed enhanced expression of inflammatory and profibrotic factors IL-6, TGF-ß1, fibronectin-1 and YKL-40, and chemokines MCP-1, MIP-1α and MIP-2, as compared to wild-type mice. The results show, for the first time, that MKP-1 protects from bleomycin-induced dermal fibrosis, suggesting that MKP-1 favorably modifies inflammation and fibrotic processes that drive the pathogenesis of scleroderma. Compounds enhancing the expression or activity of MKP-1 could thus prevent fibrotic processes in scleroderma and possess potential as a novel immunomodulative drug.

Biomarkers in the Rat Hippocampus and Peripheral Blood for an Early Stage of Mental Disorders Induced by Water Immersion Stress.

It is difficult to evaluate the pre-symptomatic state of mental disorders and prevent its onset. Since stress could be a trigger of mental disorders, it may be helpful to identify stress-responsive biomarkers (stress markers) for the evaluation of stress levels. We have so far performed omics analyses of the rat brain and peripheral blood after various kinds of stress and have found numerous factors that respond to stress. In this study, we investigated the effects of relatively moderate stress on these factors in the rat to identify stress marker candidates. Adult male Wistar rats underwent water immersion stress for 12 h, 24 h, or 48 h. Stress caused weight loss and elevated serum corticosterone levels, and alterations regarded as anxiety and/or fear-like behaviors. Reverse-transcription PCR and Western blot analyses revealed significant alterations in the expressions of hippocampal genes and proteins by the stress for no longer than 24 h, such as mitogen-activated protein kinase phosphatase 1 (MKP-1), CCAAT/enhancer-binding protein delta (CEBPD), small ubiquitin-like modifier proteins 1/sentrin-specific peptidase 5 (SENP5), matrix metalloproteinase-8 (MMP-8), kinase suppressor of Ras 1 (KSR1), and MKP-1, MMP-8, nerve growth factor receptor (NGFR). Similar alterations were observed in three genes (MKP-1, CEBPD, MMP-8) in the peripheral blood. The present results strongly suggest that these factors may serve as stress markers. The correlation of these factors in the blood and brain may enable the evaluation of stress-induced changes in the brain by blood analysis, which will contribute to preventing the onset of mental disorders.

DUSP6 Deficiency Attenuates Neurodegeneration after Global Cerebral Ischemia.

Transient global cerebral ischemia (tGCI) resulting from cardiac arrest causes selective neurodegeneration in hippocampal CA1 neurons. Although the effect is clear, the underlying mechanisms directing this process remain unclear. Previous studies have shown that phosphorylation of Erk1/2 promotes cell survival in response to tGCI. DUSP6 (also named MKP3) serves as a cytosolic phosphatase that dephosphorylates Erk1/2, but the role of DUSP6 in tGCI has not been characterized. We found that DUSP6 was specifically induced in the cytoplasm of hippocampal CA1 neurons 4 to 24 h after tGCI. DUSP6-deficient mice showed normal spatial memory acquisition and retention in the Barnes maze. Impairment of spatial memory acquisition and retention after tGCI was attenuated in DUSP6-deficient mice. Neurodegeneration after tGCI, revealed by Fluoro-Jade C and H&E staining, was reduced in the hippocampus of DUSP6-deficient mice and DUSP6 deficiency enhanced the phosphorylation and nuclear translocation of Erk1/2 in the hippocampal CA1 region. These data support the role of DUSP6 as a negative regulator of Erk1/2 signaling and indicate the potential of DUSP6 inhibition as a novel therapeutic strategy to treat neurodegeneration after tGCI.

Dual control of MAPK activities by AP2C1 and MKP1 MAPK phosphatases regulates defence responses in Arabidopsis.

Mitogen-activated protein kinase (MAPK) cascades transmit environmental signals and induce stress and defence responses in plants. These signalling cascades are negatively controlled by specific Ser/Thr protein phosphatases of the type 2C (PP2C) and dual-specificity phosphatase (DSP) families that inactivate stress-induced MAPKs; however, the interplay between phosphatases of these different types has remained unknown. This work reveals that different Arabidopsis MAPK phosphatases, the PP2C-type AP2C1 and the DSP-type MKP1, exhibit both specific and overlapping functions in plant stress responses. Each single mutant, ap2c1 and mkp1, and the ap2c1 mkp1 double mutant displayed enhanced stress-induced activation of the MAPKs MPK3, MPK4, and MPK6, as well as induction of a set of transcription factors. Moreover, ap2c1 mkp1 double mutants showed an autoimmune-like response, associated with increased levels of the stress hormones salicylic acid and ethylene, and of the phytoalexin camalexin. This phenotype was reduced in the ap2c1 mkp1 mpk3 and ap2c1 mkp1 mpk6 triple mutants, suggesting that the autoimmune-like response is due to MAPK misregulation. We conclude that the evolutionarily distant MAPK phosphatases AP2C1 and MKP1 contribute crucially to the tight control of MAPK activities, ensuring appropriately balanced stress signalling and suppression of autoimmune-like responses during plant growth and development.

Dexamethasone Attenuates the Expression of MMP-13 in Chondrocytes through MKP-1.

Mitogen-activated protein kinase phosphatase-1 (MKP-1) is upregulated in inflammation and reduces the activity of proinflammatory mitogen-activated protein kinases (MAP kinases) by dephosphorylation. MAP kinases are intracellular signaling pathways that mediate the cellular effects of proinflammatory cytokines. In the present study, we investigated the effects of the glucocorticoid dexamethasone on the expression of catabolic enzymes in chondrocytes and tested the hypothesis that these effects are mediated through MKP-1. Dexamethasone was found to significantly attenuate the expression of matrix metalloproteinase (MMP)-13 in human OA chondrocytes as well as in chondrocytes from MKP-1 WT mice, but not in chondrocytes from MKP-1 KO mice. Dexamethasone also increased the expression of MKP-1 in murine and human OA chondrocytes. Furthermore, p38 MAP kinase inhibitors significantly attenuated MMP-13 expression in human OA chondrocytes, while JNK MAP kinase inhibitors had no effect. The results indicate that the effect of dexamethasone on MMP-13 expression in chondrocytes was mediated by an MKP-1 and p38 MAP kinase-dependent manner. These findings, together with previous results, support the concept of MKP-1 as a protective factor in articular chondrocytes in inflammatory conditions and as a potential drug target to treat OA.

Salicylate Sodium Suppresses Monocyte Chemoattractant Protein-1 Production by Directly Inhibiting Phosphodiesterase 3B in TNF-α-Stimulated Adipocytes.

As a worldwide health issue, obesity is associated with the infiltration of monocytes/macrophages into the adipose tissue causing unresolved inflammation. Monocyte chemoattractant protein-1 (MCP-1) exerts a crucial effect on obesity-related monocytes/macrophages infiltration. Clinically, aspirin and salsalate are beneficial for the treatment of metabolic diseases in which adipose tissue inflammation plays an essential role. Herein, we investigated the effect and precise mechanism of their active metabolite salicylate on TNF-α-elevated MCP-1 in adipocytes. The results indicated that salicylate sodium (SAS) could lower the level of MCP-1 in TNF-α-stimulated adipocytes, which resulted from a previously unrecognized target phosphodiesterase (PDE), 3B (PDE3B), rather than its known targets IKKß and AMPK. The SAS directly bound to the PDE3B to inactivate it, thus elevating the intracellular cAMP level and activating PKA. Subsequently, the expression of MKP-1 was increased, which led to the decrease in p-EKR and p-p38. Both PDE3B silencing and the pharmacological inhibition of cAMP/PKA compromised the suppressive effect of SAS on MCP-1. In addition to PDE3B, the PDE3A and PDE4B activity was also inhibited by SAS. Our findings identify a previously unrecognized pathway through which SAS is capable of attenuating the inflammation of adipocytes.

CSF-CN contributes to cancer-induced bone pain via the MKP-1-mediated MAPK pathway.

Pain is a major complication of cancer and significantly affects the quality of life. Cerebrospinal fluid-contacting nucleus (CSF-CN) has been reported to be involved in the development of neuropathic pain and inflammatory pain. However, whether CSF-CN contributes to cancer-induced bone pain (CIBP) remains unknown. In this study, we aimed to illustrate the role of CSF-CN in the pathogenesis of CIBP and identify its potential mechanism via the MKP-1-mediated MAPK pathway. The Walker 256 cancer cells were injected into the tibia cavity of female Sprague-Dawley rats to induce CIBP models. Intracerebroventricular injection of cholera toxin subunit B- saporin (CB-SAP) was performed to "knockout" the CSF-CN. Morphine and LV-MKP-1 were applied. Mechanical and thermal hyperalgesia behaviors, double immunofluorescence staining and Western blot were conducted after CIBP induction. The results revealed that CIBP significantly reduced the mechanical withdrawal threshold and the thermal threshold. Double immunofluorescence staining revealed that c-Fos-positive neurons in CSF-CN were significantly higher in the CIBP group than that in the sham group. Targeted ablation of CSF-CN dramatically aggravated pain sensitivity. Moreover, MKP-1 was down-regulated in the CSF-CN after CIBP induction. Pharmacological intervention with morphine significantly ameliorated the mechanical and thermal hyperalgesia through reversing the down-expression of MKP-1 in the CSF-CN on day 14 after CIBP induction. Mechanically, overexpression of MKP-1 by LV-MKP-1 injection significantly relieved CIBP via inhibiting the expression of phosphorylated p38, which subsequently decreased the protein levels of Bax, cleaved caspase-3 and Iba-1, and reduced the mRNA levels of IL-1ß, TNF-α and IL-6 in CSF-CN. In conclusion, CSF-CN contributed to CIBP via regulating the MKP-1-mediated p38-MAPK pathway. Future therapy targeting the expression of MKP-1 in the CSF-CN may be a promising new choice.

MAP kinase phosphatase MKP-1 regulates p-ERK1/2 signaling pathway with fluoride treatment.

Dental fluorosis is characterized by hypomineralization of tooth enamel caused by ingestion of excessive fluoride during enamel formation. Excess fluoride could have effects on the ERK signaling, which is essential for the ameloblasts differentiation and tooth development. MAP kinase phosphatase-1 (MKP-1) plays a critical role in regulating ERK related kinases. However, the role of MKP-1 in ameloblast and the mechanisms of MKP-1/ERK signaling in the pathogenesis of dental fluorosis are incompletely understood. Here, we adopted an in vitro fluorosis cell model using murine ameloblasts-like LS8 cells by employing sodium fluoride (NaF) as inducer. Using this system, we demonstrated that fluoride exposure led to an inhibition of p-MEK and p-ERK1/2 with a subsequent increase in MKP-1 expression in a dose-dependent manner. We further identified, under high dose fluoride, MKP-1 acted as a negative regulator of the fluoride-induced p-ERK1/2 signaling, leading to downregulation of CREB, c-myc, and Elk-1. Our results identify a novel MKP-1/ERK signaling mechanism that regulates dental fluorosis and provide a framework for studying the molecular mechanisms of intervention and fluorosis remodeling under normal and pathological conditions. MKP-1 inhibitors may prove to be a benefit therapeutic strategy for dental fluorosis treatment.

A dual-specificity phosphatase, MAP kinase phosphatase 1, positively regulates blue light-mediated seedling development in Arabidopsis.

MAIN CONCLUSION: A dual-specificity phosphatase MKP1 negatively regulates the activity of MPK6 by dephosphorylating it and acts as a positive regulator of blue light (BL)-mediated photomorphogenic development in Arabidopsis. Reversible phosphorylation of proteins is one of the major post-translational modifications in nearly all signaling pathways in plants. MAP kinase phosphatases are very crucial in the regulation of MAPKs as they dephosphorylate both threonine (Thr) and tyrosine (Tyr) residues within the T-X-Y motif of active MAPKs. Therefore, to gain insight of involvement of MAP kinase phosphatases in the regulation of light signaling, we searched for the potential phosphatase which may regulate the function of MPK6, a negative regulator of blue light (BL)-mediated photomorphogenic development. We report here the identification of a dual-specificity phosphatase, MAP kinase phosphatase 1 (MKP1) as a positive regulator of BL-mediated seedling development. Overexpression of MKP1 enhances the BL-induced inhibition of hypocotyl elongation and displays more opened cotyledons. We also show that MKP1OE accumulates more pigments and positively affects the expression of downstream light-related genes in response to BL. In vitro and in vivo evidences also demonstrate that MKP1 not only interacts with but also dephosphorylates MPK6 in BL. In addition, MKP1 regulates stability as well as activity of MPK6 upon BL. Taken together our study highlights the important role of phosphatases in the regulation of a signaling pathway and identifies the role of MKP1 in the negative regulation of MPK6 activity leading to a change in BL-induced photomorphogenic responses.

Transcriptome analysis of potential candidate genes and molecular pathways in colitis-associated colorectal cancer of Mkp-1-deficient mice.

BACKGROUND: The nuclear phosphatase mitogen-activate protein kinase phosphatase-1 (MKP-1) is a key negative regulator of the innate immune response through the regulation of the biosynthesis of proinflammatory cytokines. In colorectal cancer (CRC), which is induced mainly by chronic inflammation, Mkp-1 overexpression was found in addition to disturbances in Mkp-1 functions, which may play a role in cancer development in different types of tumors. However, the potential molecular mechanisms by which Mkp-1 influences CRC development is not clear. Here, we performed global gene expression profiling of Mkp-1 KO mice using RNA sequencing (RNA-seq) to explore the role of Mkp-1 in CRC progression using transcriptome analysis. METHODS: Azoxymethane/dextran sodium sulfate (AOM/DSS) mouse models were used to examine the most dramatic molecular and signaling changes that occur during different phases of CRC development in wild-type mice and Mkp-1 KO mice. Comprehensive bioinformatics analyses were used to elucidate the molecular processes regulated by Mkp-1. Differentially expressed genes (DEGs) were identified and functionally analyzed by Gene Ontology (GO), Kyoto Enrichment of Genes and Genomes (KEGG). Then, protein-protein interaction (PPI) network analysis was conducted using the STRING database and Cytoscape software. RESULTS: Persistent DEGs were different in adenoma and carcinoma stage (238 & 251, respectively) and in WT and MKp-1 KO mice (221& 196, respectively). Mkp-1 KO modulated key molecular processes typically activated in cancer, in particular, cell adhesion, ion transport, extracellular matrix organization, response to drug, response to hypoxia, and response to toxic substance. It was obvious that these pathways are closely associated with cancer development and metastasis. From the PPI network analyses, nine hub genes associated with CRC were identified. CONCLUSION: These findings suggest that MKp-1 and its hub genes may play a critical role in cancer development, prognosis, and determining treatment outcomes. We provide clues to build a potential link between Mkp-1 and colitis-associated tumorigenesis and identify areas requiring further investigation.

Pseudophosphatases as Regulators of MAPK Signaling.

Mitogen-activated protein kinase (MAPK) signaling pathways are highly conserved regulators of eukaryotic cell function. These enzymes regulate many biological processes, including the cell cycle, apoptosis, differentiation, protein biosynthesis, and oncogenesis; therefore, tight control of the activity of MAPK is critical. Kinases and phosphatases are well established as MAPK activators and inhibitors, respectively. Kinases phosphorylate MAPKs, initiating and controlling the amplitude of the activation. In contrast, MAPK phosphatases (MKPs) dephosphorylate MAPKs, downregulating and controlling the duration of the signal. In addition, within the past decade, pseudoenzymes of these two families, pseudokinases and pseudophosphatases, have emerged as bona fide signaling regulators. This review discusses the role of pseudophosphatases in MAPK signaling, highlighting the function of phosphoserine/threonine/tyrosine-interacting protein (STYX) and TAK1-binding protein (TAB 1) in regulating MAPKs. Finally, a new paradigm is considered for this well-studied cellular pathway, and signal transduction pathways in general.

An integrated PKD1-dependent signaling network amplifies IRE1 prosurvival signaling.

Following the accumulation of improperly folded proteins in the endoplasmic reticulum (ER), a condition known as ER stress in this compartment triggers an adaptive signaling pathway referred to as the unfolded protein response (UPR). The UPR aims at restoring ER homeostasis; if the ER stress cannot be resolved, apoptosis is triggered. However, the mechanisms responsible for regulating the balance between cell life and death decisions that occur after exposure to ER stress remain unclear. Protein kinase D1 (PKD1) has been reported to initiate protective signaling against oxidative stress or ischemia, two conditions that impinge on the induction of ER stress. In addition, the high levels of expression of PKD1, observed in highly proliferative cancers and tumors with poor prognosis, contribute to enhanced resistance to chemotherapy. In this study, we show that the ER stress inducers tunicamycin and thapsigargin lead to the activation of PKD1 in human prostate cancer PC-3 cells and in hepatoma HepG2 cells through a PKCδ-dependent mechanism. Moreover, our data indicate that PKD1 is required for the stabilization of inositol-requiring enzyme 1 (IRE1) and the subsequent regulation of its activity. PKD1 activation contributes to the phosphorylation of mitogen-activated protein kinase phosphatase 1, resulting in decreased IRE1-mediated c-Jun N-terminal kinase activation. This study unveils the existence of a novel PKD1-dependent prosurvival mechanism that is activated upon ER stress and selectively enhances IRE1 prosurvival signaling.

TRIM59, amplified in ovarian cancer, promotes tumorigenesis through the MKP3/ERK pathway.

Tripartite motif containing 59 (TRIM59) functions as an oncoprotein in various human cancers including ovarian cancer. In this study, we found that TRIM59 gene amplification was prevalent in ovarian cancer tissues, and its amplification was significantly correlated with poorer overall survival. Moreover, knockdown of TRIM59 in SKOV3 and OVCAR3 cells, which had relatively high level of TRIM59, suppressed glucose uptake and lactate production. TRIM59 knockdown also decreased the expression of c-Myc and lactate dehydrogenase A, and the phosphorylation of extracellular signal-regulated kinase (ERK). TRIM59 overexpression in A2780 cells, which expressed low level of TRIM59, showed reverse effects. Notably, treatment with an ERK inhibitor (PD98059) completely abolished the oncogenic effects of TRIM59 overexpression. Interestingly, TRIM59 increased the ubiquitination of MAP kinase phosphatase 3 (MKP3), which may dephosphorylate and inactivate ERK. Ectopic expression of MKP3 inhibited the promoting effects of TRIM59 on glycolysis and the phosphorylation of ERK. TRIM59 protein expression was negatively correlated with MKP3 protein expression in ovarian cancer tissues. Finally, TRIM59 amplification potently affected the anticancer effect of 3-bromopyruvate, an inhibitor of glycolysis, in ovarian cancer cells and patient-derived xenograft. In conclusion, these results suggest that TRIM59 may regulate glycolysis in ovarian cancer via the MKP3/ERK pathway.

MKP1 reduces neuroinflammation via inhibiting endoplasmic reticulum stress and mitochondrial dysfunction.

MAP kinase phosphatase 1 (MKP1) has been identified as an antiapoptotic protein via sustaining mitochondrial function. However, the role of MKP1 in neuroinflammation has not been fully understood. The aim of this study is to figure out the influence of MKP1 in lipopolysaccharide (LPS)-treated microglia BV-2 cells and investigate whether MKP1 reduces BV-2 cell death via modulating endoplasmic reticulum (ER) stress and mitochondrial dysfunction. The results of this study demonstrated that MKP1 was rapidly downregulated after exposure to LPS. However, the transfection of MKP1 adenovirus could reverse cell viability and attenuate LPS-mediated BV-2 cell apoptosis. Mechanistically, MKP1 overexpression alleviated ER stress and corrected LPS-induced calcium overloading. Besides, MKP1 adenovirus transfection also reversed mitochondrial bioenergetics, maintained mitochondrial membrane potential, and blocked mitochondria-initiated apoptosis signals. Furthermore, we found that MKP1 overexpression is associated with inactivation of mitogen-activated protein kinase-c-Jun N-terminal kinase (MAPK-JNK) pathway. Interestingly, the activation of MAPK-JNK pathway could abolish the protective effects of MKP1 on BV-2 cells survival and mitochondrial function in the presence of LPS. Altogether, our results identified MKP1 as a primary defender of neuroinflammation via modulating ER stress and mitochondrial function in a manner dependent on MAPK-JNK pathway. These findings may open a new window for the treatment of neuroinflammation in the clinical setting.

SIRT2 is involved in cisplatin-induced acute kidney injury through regulation of mitogen-activated protein kinase phosphatase-1.

BACKGROUND: Activation of mitogen-activated protein kinase phosphatase-1 (MKP-1), a dual-specificity protein phosphatase, regulates mitogen-activated protein kinase signaling. C-Jun N-terminal kinase (JNK) and p38 are activated in cisplatin-induced renal injury. However, the change of MKP-1 expression in cisplatin-induced renal injury and the regulatory effect of sirtuin 2 (SIRT2), a nicotinamide adenine dinucleotide-dependent deacetylase, on MKP-1 remains unknown. METHODS: To address these issues, we used constitutional Sirt2 knockout (KO) mice, transgenic (TG) mice with increased expression of SIRT2 specifically in proximal tubular epithelial cellsand wild-type (WT) mice. Cisplatin nephrotoxicity was induced by intraperitoneal injection of cisplatin. RESULTS: MKP-1 expression in the kidney was decreased after cisplatin treatment. Cisplatin-induced downregulation of MKP-1 was reversed in Sirt2 KO mice kidney and further decreased in Sirt2 TG mice kidney. We observed similar phenomenon with SIRT2-knockdown or SIRT2-overexpressed tubular epithelial cells. Phosphorylation of p38 and JNK, a downstream signal pathway of MKP-1, increased in WT mice kidney following treatment with cisplatin. A decrease in SIRT2 suppressed cisplatin-induced phosphorylation of p38 and JNK in kidney and tubular epithelial cells. Overexpression of SIRT2 further increased phosphorylation of p38 and JNK in kidney and tubular epithelial cells. Acetylation of MKP-1 was significantly increased in SIRT2-knockdown cells and decreased in SIRT2-overexpressed cells after cisplatin stimulation. Sirt2 KO mice and Sirt2 TG mice showed amelioration and aggravation of renal injury, apoptosis, necroptosis and inflammation induced by cisplatin. CONCLUSION: Our data show that SIRT2 is associated with cisplatin-induced renal injury through regulation of MKP-1 expression.