Role for DUSP1 (dual-specificity protein phosphatase 1) in the regulation of autophagy

Accumulating evidence suggests that mitogen-activated protein kinases (MAPKs) regulate macroautophagy/autophagy. However, the involvement of dual-specificity protein phosphatases (DUSPs), endogenous inhibitors for MAPKs, in autophagy remains to be determined. Here we report that DUSP1/MKP-1, the founding member of the DUSP family, plays a critical role in regulating autophagy. Specifically, we demonstrate that DUSP1 knockdown by shRNA in human ovarian cancer CAOV3 cells and knockout in murine embryonic fibroblasts, increases both basal and rapamycin-increased autophagic flux. Overexpression of DUSP1 had the opposite effect. Importantly, knockout of Dusp1 promoted phosphorylation of ULK1 at Ser555, and BECN1/Beclin 1 at Ser15, and the association of PIK3C3/VPS34, ATG14, BECN1 and MAPK, leading to the activation of the autophagosome-initiating class III phosphatidylinositol 3-kinase (PtdIns3K) complex. Furthermore, knockdown and pharmacological inhibitor studies indicated that DUSP1-mediated suppression of autophagy reflected inactivation of the MAPK1-MAPK3 members of the MAPK family. Knockdown of DUSP1 sensitized CAOV3 cells to rapamycin-induced antigrowth activity. Moreover, CAOV3-CR cells, a line that had acquired cisplatin resistance, exhibited an elevated DUSP1 level and were refractory to rapamycin-induced autophagy and cytostatic effects. Knockdown of DUSP1 in CAOV3-CR cells restored sensitivity to rapamycin. Collectively, this work identifies a previously unrecognized role for DUSP1 in regulating autophagy and suggests that suppression of DUSP1 may enhance the therapeutic activity of rapamycin.     

Functional involvement of dual specificity phosphatase 16 (DUSP16), a c-Jun N-terminal kinase-specific phosphatase, in the regulation of T helper cell differentiation

Naïve CD4⁺ T helper (Th) cells differentiate into distinct subsets of effector cells (Th1, Th2, Th17, and induced regulatory T cells (iTreg)) expressing different sets of cytokines upon encounter with presented foreign antigens. It has been well established that Th1/Th2 balance is critical for the nature of the following immune responses. Previous reports have demonstrated important roles of c-Jun N-terminal kinase (JNK) in Th1/Th2 balance, whereas the regulatory mechanisms of JNK activity in Th cells have not been elucidated. Here, we show that dual specificity phosphatase 16 (DUSP16, also referred to as MKP-M or MKP-7), which preferentially inactivates JNK, is selectively expressed in Th2 cells. In the in vitro differentiation assay of naïve CD4⁺ cells, DUSP16 expression is up-regulated during Th2 differentiation and down-regulated during Th1 differentiation. Chromatin immunoprecipitation revealed the increased acetylation of histone H3/H4 at the dusp16 gene promoter in CD4⁺ T cells under the Th2 condition. Adenoviral transduction of naïve CD4⁺ T cells with DUSP16 resulted in increased mRNA expression of IL-4 and GATA-3 in Th2 and decreased expression of IFNγ and T-bet in Th1 differentiation. In contrast, transduction of a dominant negative form of DUSP16 had the reverse effects. Furthermore, upon immunization, T cell-specific dusp16 transgenic mice produced antigen-specific IgG2a at lower amounts, whereas DN dusp16 transgenic mice produced higher amounts of antigen-specific IgG2a accompanied by decreased amounts of antigen-specific IgG1 and IgE than those of control mice. Together, these data suggest the functional role of DUSP16 in Th1/Th2 balance.     

Transcriptional regulation of the human TATA binding protein gene

The human TATA binding protein (TBP) locus consists of a functional domain of three closely linkedhousekeeping genes (TBP, PSMB1 (proteasomal C5 subunit), and PDCD2 (programmed cell death-2)) within a 50-kb interval at chromosome position 6q27. Here we demonstrate that a genomic clone spanning the 20-kb TBP gene, with 12 kb 5' and 3' flanking sequences, was fully functional in stable, transfected L-cells harboring a single copy of this transgene, including after long-term (60 day) culture in the absence of drug selective pressure. Furthermore, we were only able to detect DNaseI hypersensitive sites at the TBP and PSMB1 promoters present within this 44-kb fragment. Our data suggest that this 44-kb genomic region possesses genetic regulatory elements that not only drive ubiquitous expression of TBP but also negate chromatin and DNA methylation induced silencing, which is normally associated with transgenes stably integrated into tissue culture cells.     

Crystal structure of the human dual specificity phosphatase 1 catalytic domain

The dual specificity phosphatase DUSP1 was the first mitogen activated protein kinase phosphatase (MKP) to be identified. It dephosphorylates conserved tyrosine and threonine residues in the activation loops of mitogen activated protein kinases ERK2, JNK1 and p38‐alpha. Here, we report the crystal structure of the human DUSP1 catalytic domain at 2.49 Å resolution. Uniquely, the protein was crystallized as an MBP fusion protein in complex with a monobody that binds to MBP. Sulfate ions occupy the phosphotyrosine and putative phosphothreonine binding sites in the DUSP1 catalytic domain.     

Mitogen-activated protein kinase phosphatase 1/dual specificity phosphatase 1 mediates glucocorticoid inhibition of osteoblast proliferation

Steroid-induced osteoporosis is a common side effect of long-term treatment with glucocorticoid (GC) drugs. GCs have multiple systemic effects that may influence bone metabolism but also directly affect osteoblasts by decreasing proliferation. This may be beneficial at low concentrations, enhancing differentiation. However, high-dose treatment produces a severe deficit in the proliferative osteoblastic compartment. We provide causal evidence that this effect of GC is mediated by induction of the dual-specificity MAPK phosphatase, MKP-1/DUSP1. Excessive MKP-1 production is both necessary and sufficient to account for the impaired osteoblastic response to mitogens. Overexpression of MKP-1 after either GC treatment or transfection ablates the mitogenic response in osteoblasts. Knockdown of MKP-1 using either immunodepletion of MKP-1 before in vitro dephosphorylation assay or short interference RNA transfection prevents inactivation of ERK by GCs. Neither c-jun N-terminal kinase nor p38 MAPK is activated by the mitogenic cocktail in 20% fetal calf serum, but their activation by a DNA-damaging agent (UV irradiation) was inhibited by either GC treatment or overexpression of MKP-1, indicating regulation of all three MAPKs by MKP-1 in osteoblasts. However, an inhibitor of the MAPK/ERK kinase-ERK pathway inhibited osteoblast proliferation whereas inhibitors of c-jun N-terminal kinase or p38 MAPK had no effect, suggesting that ERK is the MAPK that controls osteoblast proliferation. Regulation of ERK by MKP-1 provides a novel mechanism for control of osteoblast proliferation by GCs.     

Transcriptional regulation of the cartilage intermediate layer protein (CILP) gene

Cartilage intermediate layer protein (CILP) is an extracellular matrix protein abundant in cartilaginous tissues. CILP is implicated in common musculoskeletal disorders, including osteoarthritis and lumbar disc disease. Regulation of the CILP gene is largely unknown, however. We have found that CILP mRNA expression is induced by TGF-β1 and dependent upon signaling via TGF-β receptors. TGF-β1 induction of CILP is mediated by Smad3, which acts directly through cis-elements in the CILP promoter region. Pathways other than Smad3 also are involved in TGF-β1 induction of CILP. These observations, together with the finding that CILP protein binds and inhibits TGF-β1, suggest that CILP and TGF-β1 may form a functional feedback loop that controls chondrocyte metabolism.     

Crystal structure of human TMDP, a testis-specific dual specificity protein phosphatase: implications for substrate specificity

The testis- and skeletal-muscle-specific dual-specificity phosphatase (TMDP) is a member of the dual-specificity phosphatase (DSP) subgroup of protein tyrosine phosphatases. TMDP has similar activities toward both tyrosine and threonine phosphorylated substrates, and is supposed to be involved in spermatogenesis. Here, we report the crystal structure of human TMDP at a resolution of 2.4 A. In spite of high sequence similarity with other DSPs, the crystal structure of TMDP shows distinct structural motifs and surface properties. In TMDP, the alpha1-beta1 loop, a substrate recognition motif is located further away from the active site loop in comparison to prototype DSP Vaccinia H1 related phophatase (VHR), which preferentially dephosphorylates tyrosine phosphorylated substrates and down-regulates MAP kinase signaling. Residues in the active site residues of TMDP are smaller in size and more hydrophobic than those of VHR. In addition, TMDP cannot be aligned with VHR in loop beta3-alpha4. These differences in the active site of TMDP result in a flat and wide pocket structure, allowing equal binding of phosphotyrosine and phosphothreonine substrates.