Dual-specificity MAPK Phosphatases Research Articles

Characterization of angiotensin II-induced dual-specificity MAPK phosphatase gene expression changes in vascular smooth muscle cells

Characterization of angiotensin II-induced dual-specificity MAPK phosphatase gene expression changes in vascular smooth muscle cells

Suppression of mutant Kirsten-RAS (KRASG12D)-driven pancreatic carcinogenesis by dual-specificity MAP kinase phosphatases 5 and 6

The cytoplasmic phosphatase DUSP6 and its nuclear counterpart DUSP5 are negative regulators of RAS/ERK signalling. Here we use deletion of either Dusp5 or Dusp6 to explore the roles of these phosphatases in a murine model of KRASG12D-driven pancreatic cancer. By 56-days, loss of either DUSP5 or DUSP6 causes a significant increase in KRASG12D-driven pancreatic hyperplasia. This is accompanied by increased pancreatic acinar to ductal metaplasia (ADM) and the development of pre-neoplastic pancreatic intraepithelial neoplasia (PanINs). In contrast, by 100-days, pancreatic hyperplasia is reversed with significant atrophy of pancreatic tissue and weight loss observed in animals lacking either DUSP5 or DUSP6. On further ageing, Dusp6−/− mice display accelerated development of metastatic pancreatic ductal adenocarcinoma (PDAC), while in Dusp5−/− animals, although PDAC development is increased this process is attenuated by atrophy of pancreatic acinar tissue and severe weight loss in some animals before cancer could progress. Our data suggest that despite a common target in the ERK MAP kinase, DUSP5 and DUSP6 play partially non-redundant roles in suppressing oncogenic KRASG12D signalling, thus retarding both tumour initiation and progression. Our data suggest that loss of either DUSP5 or DUSP6, as observed in certain human tumours, including the pancreas, could promote carcinogenesis.

Interaction between MAPKs and MKPs in hexaploid chrysanthemum illuminates functional paralogue diversification in polyploids

Mitogen-activated protein kinases (MAPKs, also known as MPKs) regulate diverse cellular and physiological functions, and dual-specificity MAPK phosphatases (MKPs) modulate MAPK signalling through MAPK dephosphorylation and inactivation. Due to lacking of overall understanding for the regulatory networks between Chrysanthemum morifolium MKPs (CmMKPs) and C. morifolium MAPKs (CmMPKs), we systematically studied the interactions between four groups of CmMPKs and eight identified CmMKPs in chrysanthemum and found that the interaction between the specific CmMKP and the specific CmMPK differed from those in other plants. Furthermore, the expression of CmMKP1 and CmMKP1-LIKE1 showed opposite trends during the development of chrysanthemum flower buds under salt treatment and Alternaria alternata inoculation, but these genes could interact with the same CmMPKs, providing insight into the subfunctionalization of paralogues. Amino acid variations (M87V, T277P and V6L) in dual-specificity protein phosphatases (DsPTP1)-LIKE1/2/3 changed the interactions of these proteins with the four CmMPK groups in chrysanthemum, providing evidence for the de/neofunctionalization of paralogues in polyploids, suggesting that we can identify the key functional sites of proteins by studying polyploid paralogues.

Characterization of Type 1 Angiotensin II Receptor Activation Induced Dual-Specificity MAPK Phosphatase Gene Expression Changes in Rat Vascular Smooth Muscle Cells.

Activation of the type I angiotensin receptor (AT1-R) in vascular smooth muscle cells (VSMCs) plays a crucial role in the regulation of blood pressure; however, it is also responsible for the development of pathological conditions such as vascular remodeling, hypertension and atherosclerosis. Stimulation of the VSMC by angiotensin II (AngII) promotes a broad variety of biological effects, including gene expression changes. In this paper, we have taken an integrated approach in which an analysis of AngII-induced gene expression changes has been combined with the use of small-molecule inhibitors and lentiviral-based gene silencing, to characterize the mechanism of signal transduction in response to AngII stimulation in primary rat VSMCs. We carried out Affymetrix GeneChip experiments to analyze the effects of AngII stimulation on gene expression; several genes, including DUSP5, DUSP6, and DUSP10, were identified as upregulated genes in response to stimulation. Since various dual-specificity MAPK phosphatase (DUSP) enzymes are important in the regulation of mitogen-activated protein kinase (MAPK) signaling pathways, these genes have been selected for further analysis. We investigated the kinetics of gene-expression changes and the possible signal transduction processes that lead to altered expression changes after AngII stimulation. Our data shows that the upregulated genes can be stimulated through multiple and synergistic signal transduction pathways. We have also found in our gene-silencing experiments that epidermal growth factor receptor (EGFR) transactivation is not critical in the AngII-induced expression changes of the investigated genes. Our data can help us understand the details of AngII-induced long-term effects and the pathophysiology of AT1-R. Moreover, it can help to develop potential interventions for those symptoms that are induced by the over-functioning of this receptor, such as vascular remodeling, cardiac hypertrophy or atherosclerosis.

Trauma-induced regulation of VHP-1 modulates the cellular response to mechanical stress

Mechanical stimuli initiate adaptive signal transduction pathways, yet exceeding the cellular capacity to withstand physical stress results in death. The molecular mechanisms underlying trauma-induced degeneration remain unclear. In the nematode C. elegans, we have developed a method to study cellular degeneration in response to mechanical stress caused by blunt force trauma. Herein, we report that physical injury activates the c-Jun kinase, KGB-1, which modulates response elements through the AP-1 transcriptional complex. Among these, we have identified a dual-specificity MAPK phosphatase, VHP-1, as a stress-inducible modulator of neurodegeneration. VHP-1 regulates the transcriptional response to mechanical stress and is itself attenuated by KGB-1-mediated inactivation of a deubiquitinase, MATH-33, and proteasomal degradation. Together, we describe an uncharacterized stress response pathway in C. elegans and identify transcriptional and post-translational components comprising a feedback loop on Jun kinase and phosphatase activity.

TORC2/3-mediated DUSP1 upregulation is essential for human decidualization.

Decidualization is the functional transformation process of endometrium in response to ovarian steroids dedicated to support embryo development. Defective decidualization is closely associated with various pregnancy complications such as recurrent miscarriage (RM). Dual specificity MAPK phosphatases (MKPs) are a family of phosphatases specifically regulating mitogen-activated protein kinase (MAPK) signaling with dual specificity for threonine and tyrosine. Here, using RNA-seq,we found that dual specificity phosphatase 1 (DUSP1) expression was prominently elevated among the MKP family members in db-cAMP treated primary human endometrial stromal cells (ESCs). We verified that its induction by db-cAMP in ESCs was in a dose- and time-dependent manner and that primary human decidual stromal cells (DSCs) present higher expression of DUSP1 than ESCs. A protein kinase A (PKA) inhibitor H-89 abolished its induction in ESCs, but not ESI-09, an EPAC1/2 inhibitor. Knock-down of TORC2/3 but not CREB by siRNA in ESCs diminished its induction by db-cAMP. Furthermore, knock-down of DUSP1, as well as TORC2/3 by siRNA caused abnormal activation of JNK during db-cAMP induction in ESCs, accompanied by decreased IGFBP1 expression, an ESC decidualization indicator, which could be fully rescued by a JNK inhibitor SP600125. In addition, Western blot showed that DUSP1 expression was reduced in the DSCs of patients with RM, along with JNK overactivation and decreased IGFBP1 expression. In conclusion, our results demonstrated that TORC2/3-mediated DUSP1 upregulation in response to the cAMP/PKA signaling safeguards IGFBP1 expression via restraining JNK activity, indicating its involvement in ESC decidualization, and that aberrant expression of DUSP1 in DSCs might engage in the pathogenesis of RM.

Lnc-FAM84B-4 acts as an oncogenic lncRNA by interacting with protein hnRNPK to restrain MAPK phosphatases-DUSP1 expression.

The mitogen activated protein kinase (MAPK) pathway has been reported to be involved in many cancer developments. Normally, MAPK activity is self-limited between rapid phosphorylation and dephosphorylation. In abnormal conditions, however, this dynamic equilibrium is broken, trigging tumor-suppressing or -promoting roles. While dual-specificity MAPK phosphatases (MKP/DUSPs) are important for cascade control in MAPK pathway, their role in colorectal cancer (CRC) remains largely unknown. Here, we investigated lnc-FAM84B-4 and DUSP1 to systematically elucidate their underlying roles in MAPK singling pathway and functions in CRC. Upregulated lnc-FAM84B-4 was identified by re-mining CRC microarray. Functional assays were performed in vitro and in vivo. RNA-Seq, RNA pull-down, and RIP assays were used to investigate the mechanisms of Lnc-FAM84B-4 in regulating expression of DUSP1. The results indicated that Lnc-FAM84B-4 regulates MAPK pathway by restraining DUSP1 expression. Mechanistically, RNA pull-down followed by mass spectrum determined hnRNPK functions as a binding partner of lnc-FAM84B-4 in mediating DUSP1 expression. Our findings demonstrate the important role of lnc-FAM84B-4-hnRNPK-DUSP1 axis in CRC development, and suggest a therapeutic target for CRC treatment.

The p38/MKP-1 signaling axis in oral cancer: Impact of tumor-associated macrophages.

Oral squamous cell carcinomas (OSCC) constitute over 95% of all head and neck malignancies. As a key component of the tumor microenvironment (TME), chronic inflammation contributes towards the development, progression, and regional metastasis of OSCC. Tumor associated macrophages (TAMs) associated with OSSC promote tumorigenesis through the production of cytokines and pro-inflammatory factors that are critical role in the various steps of malignant transformation, including tumor growth, survival, invasion, angiogenesis, and metastasis. The mitogen-activated protein kinases (MAPKs) can regulate inflammation along with a wide range of cellular processes including cell metabolism, proliferation, motility, apoptosis, survival, differentiation and play a crucial role in cell growth and survival in physiological and pathological processes including innate and adaptive immune responses. Dual specificity MAPK phosphatases (MKPs) deactivates MAPKs. MKPs are considered as an important feedback control mechanism that limits MAPK signaling and subsequent target gene expression. This review outlines the role of MKP-1, the founding member of the MKP family, in OSCC and the TME. Herein, we summarize recent progress in understanding the regulation of p38 MAPK/MKP-1 signaling pathways via TAM-related immune responses in OSCC development, progression and treatment outcomes.

Unraveling the role of H3K4 trimethylation and lncRNA HOTAIR in SATB1 and DUSP4-dependent survival of virulent Mycobacterium tuberculosis in macrophages

The modification of chromatin influences host transcriptional programs during bacterial infection, at times skewing the balance in favor of pathogen survival. To test the role of chromatin modifications during Mycobacterium tuberculosis infection, we analysed genome-wide deposition of H3K4me3 marks in macrophages infected with either avirulent M. tuberculosis H37Ra or virulent H37Rv, by chromatin immunoprecipitation, followed by sequencing. We validated differences in association of H3K4me3 at the loci of special AT-rich sequence binding protein 1 (SATB1) and dual specificity MAP kinase phosphatase 4 (DUSP4) between H37Rv and H37Ra-infected macrophages, and demonstrated their role in regulating bacterial survival in macrophages as well as the expression of chemokines. SATB1 repressed gp91phox (an NADPH oxidase subunit) thereby regulating reactive oxygen species (ROS) generation during infection. Long non-coding RNA HOX transcript antisense RNA (HOTAIR) was upregulated in H37Ra-, but downregulated in H37Rv-infected macrophages. HOTAIR overexpression correlated with deposition of repressive H3K27me3 marks around the TSSs of DUSP4 and SATB1, suggesting that its downregulation favors the transcription of SATB1 and DUSP4. In summary, we have delineated histone modification- and lncRNA-dependent mechanisms regulating gene expression patterns facilitating survival of virulent M. tuberculosis. Our observations raise the possibility of harnessing histone-modifying enzymes to develop host-directed therapies for tuberculosis.

Flumequine-Mediated Upregulation of p38 MAPK and JNK Results in Melanogenesis in B16F10 Cells and Zebrafish Larvae.

Flumequine is a well-known second generation quinolone antibiotic that induces phototoxicity. However, the effect of flumequine on skin melanogenesis is unclear. Therefore, we, for the first time, investigated whether flumequine regulates melanogenesis. The present study showed that flumequine slightly inhibited in vitro mushroom tyrosinase activity but significantly increased extracellular and intracellular melanin content in B16F10 cells and promoted the expression of microphthalmia-associated transcription factor (MITF) and tyrosinase. Additionally, flumequine remarkably increased melanin pigmentation in zebrafish larvae without any toxicity. We also found that flumequine stimulated p38 mitogen-activated protein kinase (MAPK) and c-Jun N-terminal kinase (JNK) phosphorylation; inhibition of p38 MAPK and JNK resulted in significant downregulation of extracellular and intracellular melanin content in B16F10 cells and pigmentation of zebrafish larvae accompanied with suppression of MITF and tyrosinase expression, indicating that flumequine-mediated p38 and JNK promote melanogenesis in vitro and in vivo. According to the molecular docking prediction, flumequine targeted dual-specificity MAPK phosphatase 16 (DUSP16), which is a major negative regulator of p38 MAPK and JNK. Our findings demonstrate that flumequine induces an increase in melanin content in B16F10 cells and zebrafish larvae by activating p38 MAPK and JNK. These data show the potential of flumequine for use as an anti-vitiligo agent.

Central Roles and Regulatory Mechanisms of Dual-Specificity MAPK Phosphatases in Developmental and Stress Signaling.

Mitogen-Activated Protein Kinase (MAPK) cascades are conserved signaling modules that integrate multiple signaling pathways. One level of control on the activity of MAPKs is through their negative regulators, MAPK phosphatases (MKPs). Therefore, MKPs also play an integrative role for plants responding to diverse environmental stimulus; but the mechanism(s) by which these phosphatases contribute to specific signals remains largely unknown. In this review, we summarize recent advances in characterizing the biological functions of a sub-class of MKPs, dual-specificity phosphatases (DSPs), ranging from controlling plant growth and development to modulating stress adaptation. We also discuss putative regulatory mechanisms of DSP-type MKPs, which plants may use to control the correct level of responses at the right place and time. We highlight insights into potential regulation of cross-talk between different signaling pathways, facilitating the development of strategies for targeting such cross-talk and to help improve plant resistance against adverse environmental conditions without affecting the growth and development.

Dual-specificity MAP kinase phosphatases in health and disease

It is well established that a family of dual-specificity MAP kinase phosphatases (MKPs) play key roles in the regulated dephosphorylation and inactivation of MAP kinase isoforms in mammalian cells and tissues. MKPs provide a mechanism of spatiotemporal feedback control of these key signalling pathways, but can also mediate crosstalk between distinct MAP kinase cascades and facilitate interactions between MAP kinase pathways and other key signalling modules. As our knowledge of the regulation, substrate specificity and catalytic mechanisms of MKPs has matured, more recent work using genetic models has revealed key physiological functions for MKPs and also uncovered potentially important roles in regulating the pathophysiological outcome of signalling with relevance to human diseases. These include cancer, diabetes, inflammatory and neurodegenerative disorders. It is hoped that this understanding will reveal novel therapeutic targets and biomarkers for disease, thus contributing to more effective diagnosis and treatment for these debilitating and often fatal conditions.

Up-regulation of DUSP5 and DUSP6 by gonadotropin-releasing hormone in cultured hypothalamic neurons, GT1-7 cells.

Gonadotropin-releasing hormone (GnRH) is secreted from hypothalamic neurons (GnRH neurons) and stimulates anterior pituitary gonadotrophs to synthesize and secrete gonadotropins. In addition to gonadotrophs, GnRH neurons also express GnRH receptors, and the autocrine action of GnRH is reportedly involved in the regulation of functions of GnRH neurons. There is accumulating evidence that extracellular signal-regulated kinase (ERK), one of mitogen-activated protein kinases (MAPKs), is activated by GnRH and involved in various effects of GnRH in GnRH neurons. In the present study, we performed microarray analysis to examine the types of genes whose expression was regulated by GnRH in immortalized mouse GnRH neurons (GT1-7 cells). We found that 257 genes among 55,681 genes examined were up-regulated after 30-min treatment of GT1-7 cells with GnRH. These up-regulated genes included four dual-specificity MAPK phosphatases (DUSPs), DUSP1, DUSP2, DUSP5, and DUSP6. Reverse transcription-polymerase chain reaction analysis confirmed that the mRNA levels of DUSP5 and DUSP6 were robustly increased within 30 min. U0126, an inhibitor of ERK activation, completely inhibited the increases in the mRNA levels of DUSP5 and DUSP6. Immunoblotting analysis revealed that ERK activation peaked at 5 min and declined steeply at 60 min, whereas DUSP5 and DUSP6 proteins were increased from 60 min. It was notable that down-regulation of DUSP6 augmented GnRH-induced ERK activation approximately 1.7-fold at 60 min. These results suggested that the up-regulation of DUSP6 regulates the duration of ERK activation at least in part.

Phosphorylation of epidermal growth factor receptor at serine 1047 in cultured lung alveolar epithelial cells by bradykinin B2 receptor stimulation

Accumulating evidence indicates that epidermal growth factor receptor (EGFR) is desensitized by phosphorylation of serine 1047 (Ser1047). We and other groups have reported that stimulation of a receptor of tumor-necrosis factor α (TNFα) and Toll-like receptor 5 (TLR5) induced the phosphorylation of Ser1047 through activation of p38 mitogen-activated protein kinase (p38 MAPK) in cultured lung alveolar epithelial A549 cells. However, phosphorylation of EGFR at Ser1047 by stimulation of any G-protein coupled receptors (GPCRs) has not been reported in any cultured cells. In the present study, we first confirmed that A549 cells expressed bradykinin (BK) B2 receptor, and then, we examined whether BK treatment of A549 cells activated MAPKs and induced the phosphorylation of EGFR at Ser1047. Immunoblotting analysis and reporter gene assays indicated that BK activated the pathways of extracellular signal-regulated kinase (ERK) and p38 MAPK. Inhibitor studies suggested that Gq/11 was mainly involved in the activation of ERK and p38 MAPK. We found that stimulation of the BK B2 receptor, but not the BK B1 receptor, induced phosphorylation of EGFR at Ser1047. Pharmacological experiments indicated that both ERK and p38 MAPK were involved in the phosphorylation of EGFR. These results strongly suggested that BK regulates EGFR functions in lung alveolar epithelial cells. In addition, we found that BK treatment increased the mRNA level of dual specificity MAPK phosphatase 5 (DUSP5) in an ERK-dependent manner, which suggested that a negative feedback mechanism of ERK existed in the cells.

Rae1-mediated nuclear export of Rnc1 is an important determinant in controlling MAPK signaling.

In eukaryotic cells, RNA binding proteins (RBPs) play critical roles in regulating almost every aspect of gene expression, often shuttling between the nucleus and the cytoplasm. They are also key determinants in cell fate via controlling the target mRNAs under the regulation of various signaling pathways in response to environmental stresses. Therefore, understanding the mechanisms that couple the location of mRNA and RBPs is a major challenge in the field of gene expression and signal responses. In fission yeast, a KH-type RBP Rnc1 negatively regulates MAPK signaling activation via mRNA stabilization of the dual-specificity MAPK phosphatase Pmp1, which dephosphorylates MAPK Pmk1. Rnc1 also serves as a target of MAPK phosphorylation, which makes a feedback loop mediated by an RBP. We recently discovered that the nuclear export of Rnc1 requires mRNA-binding ability and the mRNA export factor Rae1. This strongly suggested the presence of an mRNA-export system, which recognizes the mRNA/RBP complex and dictates the location and post-transcriptional regulation of mRNA cargo. Here, we briefly review the known mechanisms of general nuclear transporting systems, with an emphasis on our recent findings on the spatial regulation of Rnc1 and its impact on the regulation of the MAPK signal transduction cascade.

Abstract 4842: TP53INP1 negatively regulates ERK1/2 via p73-dependent DUSP10 expression to promote metastasis in hepatocellular carcinoma

Abstract The recurrence and metastasis of hepatocellular carcinoma (HCC) portends a poor prognosis and represents important clinical challenges. There is a great need to identify critical factors involved in HCC metastasis that will facilitate the development of new therapeutic strategies. We have previously found that the initiation, growth and self-renewal of CD133+ liver tumors to be fine-tuned by a balance of miR-130b overexpression and tumor protein 53 inducible nuclear protein 1 (TP53INP1) down-regulation, suggesting that TP53INP1 is a critical effector driving hepatocarcinogenesis. In this study, we aimed to further investigate the role of TP53INP1 in HCC metastasis. We showed TP53INP1 to be frequently down-regulated in advanced stage IV and metastatic human HCC tumors as compared with early stage (I-III) and primary tumors. Functional studies in immortalized normal liver cell line MIHA and HCC cell line MHCC-97L found TP53INP1 suppression in HCC to promote metastasis in vitro and in vivo. To elucidate the downstream signaling mechanism by which TP53INP1 regulates HCC metastasis, a Proteome Profiler Human Phospho-Kinase Array was utilized. Phospho-ERK was found to be consistently up-regulated in HCC cell lines with TP53INP1 knocked down, with its involvement in TP53INP1-mediated metastasis subsequently validated by rescue experiments using an ERK inhibitor U0126 or shERK1/2 knockdown approach. ERK1/2 is known to be negatively regulated by a family of dual-specificity MAPK phosphatase called DUSP/MKP. Screening of a panel of DUSP/MKP family members by qPCR identified DUSP10 to be commonly down-regulated in both MIHA and MHCC-97L cells with TP53INP1 suppressed as compared to controls. The importance of DUSP10 inactivation on ERK in TP53INP1-mediated HCC was substantiated by rescue experiments whereby DUSP10 ectopic expression in TP53INP1 suppressed cells reversed up-regulated phospho-ERK expression and enhanced HCC aggressiveness. Subsequent analysis of the DUSP10 promoter region by open-access database revealed four putative binding sites for p73, of which transcriptional activity has previously been found to be modulated by TP53INP1. Chromatin immunoprecipitation and luciferase reporter assays collectively demonstrated that TP53INP1 is vital for p73 transcriptional activity of DUSP10. Taken together, TP53INP1 down-regulation promotes HCC metastasis through a p73-dependent DUSP10/ERK signaling pathway. Note: This abstract was not presented at the meeting. Citation Format: Kai Yu Ng, Lok Hei Chan, Stella Chai, Man Tong, Xin Yuan Guan, Nikki P Lee, Yun Fei Yuan, Dan Xie, Terence K Lee, Alice Carrier, Nelson J Dusetti, Stephanie Ma. TP53INP1 negatively regulates ERK1/2 via p73-dependent DUSP10 expression to promote metastasis in hepatocellular carcinoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 4842. doi:10.1158/1538-7445.AM2017-4842

Regulation of atypical MAP kinases ERK3 and ERK4 by the phosphatase DUSP2

The atypical MAP kinases ERK3 and ERK4 are activated by phosphorylation of a serine residue lying within the activation loop signature sequence S-E-G. However, the regulation of ERK3 and ERK4 phosphorylation and activity is poorly understood. Here we report that the inducible nuclear dual-specificity MAP kinase phosphatase (MKP) DUSP2, a known regulator of the ERK and p38 MAPKs, is unique amongst the MKP family in being able to bind to both ERK3 and ERK4. This interaction is mediated by a conserved common docking (CD) domain within the carboxyl-terminal domains of ERK3 and ERK4 and the conserved kinase interaction motif (KIM) located within the non-catalytic amino terminus of DUSP2. This interaction is direct and results in the dephosphorylation of ERK3 and ERK4 and the stabilization of DUSP2. In the case of ERK4 its ability to stabilize DUSP2 requires its kinase activity. Finally, we demonstrate that expression of DUSP2 inhibits ERK3 and ERK4-mediated activation of its downstream substrate MK5. We conclude that the activity of DUSP2 is not restricted to the classical MAPK pathways and that DUSP2 can also regulate the atypical ERK3/4-MK5 signalling pathway in mammalian cells.

Dual-specificity phosphatase 5 controls the localized inhibition, propagation, and transforming potential of ERK signaling

Deregulated extracellular signal-regulated kinase (ERK) signaling drives cancer growth. Normally, ERK activity is self-limiting by the rapid inactivation of upstream kinases and delayed induction of dual-specificity MAP kinase phosphatases (MKPs/DUSPs). However, interactions between these feedback mechanisms are unclear. Here we show that, although the MKP DUSP5 both inactivates and anchors ERK in the nucleus, it paradoxically increases and prolongs cytoplasmic ERK activity. The latter effect is caused, at least in part, by the relief of ERK-mediated RAF inhibition. The importance of this spatiotemporal interaction between these distinct feedback mechanisms is illustrated by the fact that expression of oncogenic BRAFV600E, a feedback-insensitive mutant RAF kinase, reprograms DUSP5 into a cell-wide ERK inhibitor that facilitates cell proliferation and transformation. In contrast, DUSP5 deletion causes BRAFV600E-induced ERK hyperactivation and cellular senescence. Thus, feedback interactions within the ERK pathway can regulate cell proliferation and transformation, and suggest oncogene-specific roles for DUSP5 in controlling ERK signaling and cell fate.

Identification and functional analysis of dual-specificity MAP kinase phosphatase 6 gene (dusp6) in response to immune challenges in Japanese flounder Paralichthys olivaceus

Dual-specificity phosphatase 6 (Dusp6) is a member of mitogen-activated protein kinase (MAPK) phosphatases that play crucial roles in regulating MAPK signaling and immune response. The immunological relevance of Dusp6 in fish, however, remains largely uncharacterized. In the present study, a full-length Japanese flounder dusp6 cDNA ortholog, termed PoDusp6, was identified and characterized from Paralichthys olivaceus. The deduced PoDusp6 protein is comprised of 383 amino acids with a conserved N-terminal regulatory rhodanese homology domain and a C-terminal catalytic domain. Immunofluorescence microscopy revealed that PoDusp6 protein is mainly localized in cytoplasm. Sequence analysis indicates that PoDusp6 is highly conserved (>70% identity) throughout the evolution from teleost to mammals. In unstimulated conditions, PoDusp6 mRNA was present in all examined tissues and showed the highest expression in Japanese flounder head kidney macrophages (HKMs). Immune challenge experiments revealed that the expression of PoDusp6 was down-regulated at the early stage after LPS and poly(I:C) stimulations but significantly up-regulated at the later stage in the HKMs. The similar expression pattern was also observed in the Japanese flounder immune-related tissues including head kidney, gill and spleen upon bacterial challenge with Edwardsiella tarda. Overexpression of PoDusp6 in Japanese flounder FG-9307 cells led to a significant down-regulation of proinflammatory cytokine genes IL-1beta, TNF-alpha and IFN-gamma, and antiviral gene Mx. Interestingly, inhibition of Dusp6 activity also down-regulated the LPS-induced IL-beta gene expression but did not affected on the LPS-induced IFN-gamma and TNF-alpha expression in the HKMs. Our findings suggest that the expression of PoDusp6 is modulated by immune stimuli and PoDusp6 may act as an essential modulator in fish inflammatory response.

Regulation of cardiac hypertrophy and remodeling through the dual-specificity MAPK phosphatases (DUSPs)

Mitogen-activated protein kinases (MAPKs) play a critical role in regulating cardiac hypertrophy and remodeling in response to increased workload or pathological insults. The spatiotemporal activities and inactivation of MAPKs are tightly controlled by a family of dual-specificity MAPK phosphatases (DUSPs). Over the past 2 decades, we and others have determined the critical role for selected DUSP family members in controlling MAPK activity in the heart and the ensuing effects on ventricular growth and remodeling. More specifically, studies from mice deficient for individual Dusp genes as well as heart-specific inducible transgene-mediated overexpression have implicated select DUSPs as essential signaling effectors in the heart that function by dynamically regulating the level, subcellular and temporal activities of the extracellular signal-regulated kinases (ERKs), c-Jun N-terminal kinases (JNKs) and p38 MAPKs. This review summarizes recent literature on the physiological and pathological roles of MAPK-specific DUSPs in regulating MAPK signaling in the heart and the effect on cardiac growth and remodeling.