DUSP3/VHR: A Druggable Dual Phosphatase for Human Diseases

Dual-specificity phosphatase 3 deletion promotes obesity, non-alcoholic steatohepatitis and hepatocellular carcinoma

Non-alcoholic fatty liver disease (NAFLD) is the most common chronic hepatic pathology in Western countries. It encompasses a spectrum of conditions ranging from simple steatosis to more severe and progressive non-alcoholic steatohepatitis (NASH) that can lead to hepatocellular carcinoma (HCC). Obesity and related metabolic syndrome are important risk factors for the development of NAFLD, NASH and HCC. DUSP3 is a small dual-specificity protein phosphatase with a poorly known physiological function. We investigated its role in metabolic syndrome manifestations and in HCC using a mouse knockout (KO) model. While aging, DUSP3-KO mice became obese, exhibited insulin resistance, NAFLD and associated liver damage. These phenotypes were exacerbated under high fat diet (HFD). In addition, DEN administration combined to HFD led to rapid HCC development in DUSP3-KO compared to wild type (WT) mice. DUSP3-KO mice had more serum triglycerides, cholesterol, AST and ALT compared to control WT mice under both regular chow diet (CD) and HFD. The level of fasting insulin was higher compared to WT mice, though, fasting glucose as well as glucose tolerance were normal. At the molecular level, HFD led to decreased expression of DUSP3 in WT mice. DUSP3 deletion was associated with increased and consistent phosphorylation of the insulin receptor (IR) and with higher activation of the downstream signaling pathway. In conclusion, our results support a new role for DUSP3 in obesity, insulin resistance, NAFLD and liver damage.

Nucleophosmin Protein Dephosphorylation by DUSP3 Is a Fine-Tuning Regulator of p53 Signaling to Maintain Genomic Stability

The dual-specificity phosphatase 3 (DUSP3), an atypical protein tyrosine phosphatase (PTP), regulates cell cycle checkpoints and DNA repair pathways under conditions of genotoxic stress. DUSP3 interacts with the nucleophosmin protein (NPM) in the cell nucleus after UV-radiation, implying a potential role for this interaction in mechanisms of genomic stability. Here, we show a high-affinity binding between DUSP3-NPM and NPM tyrosine phosphorylation after UV stress, which is increased in DUSP3 knockdown cells. Specific antibodies designed to the four phosphorylated NPM’s tyrosines revealed that DUSP3 dephosphorylates Y29, Y67, and Y271 after UV-radiation. DUSP3 knockdown causes early nucleolus exit of NPM and ARF proteins allowing them to disrupt the HDM2-p53 interaction in the nucleoplasm after UV-stress. The anticipated p53 release from proteasome degradation increased p53-Ser15 phosphorylation, prolonged p53 half-life, and enhanced p53 transcriptional activity. The regular dephosphorylation of NPM’s tyrosines by DUSP3 balances the p53 functioning and favors the repair of UV-promoted DNA lesions needed for the maintenance of genomic stability.

Protein tyrosine phosphatases (PTPs) in diabetes: causes and therapeutic opportunities

Protein tyrosine phosphatases (PTPs) have an emerging paradigm for the development of antidiabetic drugs. Herein, we provide a comprehensive overview of the relevance of PTPs to type 2 diabetes (T2D) and the therapeutic opportunities thereof, while critically evaluating the potential challenges for PTP inhibitors to be next generation antidiabetics. This review briefly discusses the structure and function of PTPs. An account of importance and relevance of PTPs in various human diseases is presented with special attention to diabetes. The PTPs relevant to T2D have been targeted by small molecule inhibitors such as natural products and synthetic compounds as well as antisense nucleic acids. This review will give better understanding of the important concepts helpful in outlining the strategies for the development of new therapeutic agents with promising antidiabetic activities.

UV Radiation-induced Impairment of Cellular Morphology and Motility is Enhanced by DUSP3/VHR Loss and FAK Activation

DUSP3 is a phosphatase expressed and active in several tissues that dephosphorylates tyrosine residues in many regulatory proteins of cellular activities such as proliferation, survival, and cell death. Recently, two new independent functions were assigned to this enzyme: dephosphorylation of focal adhesion kinase (FAK) and regulation of nucleotide-excision repair (NER) pathway. Genotoxic stress by UV radiation is known to affect cell morphology, adhesion, and migration for affecting, for example, the Rho GTPases that regulate actin cytoskeleton. This work investigated the intersection of DUSP3 function, XPA protein activity, and UV toxicity by examining cell migration, FAK, and SRC kinase phosphorylation status, in addition to cell morphology, in fibroblast cells proficient (MRC-5) or deficient (XPA) of the NER pathway. DUSP3 loss reduced cell migration of normal cells, which was stimulated by the genotoxic stress, effects evidenced in presence of serum mitogenic stimulus. However, NER-deficient cells migration response was the opposite since DUSP3 loss increased migration, especially after cells being exposed to UV stress. The levels of pFAK(Y397) peaked 15 min and 1 h after UV radiation in normal cells, but only slightly increased in repair-deficient cells. However, the DUSP3 knockdown strongly raised pFAK(Y397) levels in both cells, but especially in XPA cells as supported by the higher SRC activity. These effects impacted on the dynamics of actin-based structures formation, such as stress fibres, apparently dependent on DUSP3 and DNA-repair (NER) proficiency of the cells. Altogether our findings suggest this dual-phosphatase is bridging gaps between the complex regulation of cell morphology, motility, and genomic stability.

A Review of DUSP26: Structure, Regulation and Relevance in Human Disease

Dual specificity phosphatases (DUSPs) play a crucial role in the regulation of intracellular signalling pathways, which in turn influence a broad range of physiological processes. DUSP malfunction is increasingly observed in a broad range of human diseases due to deregulation of key pathways, most notably the MAP kinase (MAPK) cascades. Dual specificity phosphatase 26 (DUSP26) is an atypical DUSP with a range of physiological substrates including the MAPKs. The residues that govern DUSP26 substrate specificity are yet to be determined; however, recent evidence suggests that interactions with a binding partner may be required for DUSP26 catalytic activity. DUSP26 is heavily implicated in cancer where, akin to other DUSPs, it displays both tumour-suppressive and -promoting properties, depending on the context. Here we review DUSP26 by evaluating its transcriptional patterns, protein crystallographic structure and substrate binding, as well as its physiological role(s) and binding partners, its role in human disease and the development of DUSP26 inhibitors.

DUSP3 maintains genomic stability and cell proliferation by modulating NER pathway and cell cycle regulatory proteins

The DUSP3 phosphatase regulates cell cycle, proliferation, apoptosis and senescence of different cell types, lately shown as a mediator of DNA repair processes. This work evaluated the impact of DUSP3 loss of function (lof) on DNA repair-proficient fibroblasts (MRC-5), NER-deficient cell lines (XPA and XPC) and translesion DNA synthesis (TLS)-deficient cells (XPV), after UV-radiation stress. The levels of DNA strand breaks, CPDs and 6-4-PPs have accumulated over time in all cells under DUSP3 lof, with a significant increase in NER-deficient lines. The inefficient repair of these lesions increased sub-G1 population of XPA and XPC cells 24 hours after UV treatment, notably marked by DUSP3 lof, which is associated with a reduced cell population in G1, S and G2/M phases. It was also detected an increase in S and G2/M populations of XPV and MRC-5 cells after UV-radiation exposure, which was slightly attenuated by DUSP3 lof due to a discrete increase in sub-G1 cells. The cell cycle progression was accompanied by changes in the levels of the main Cyclins (A1, B1, D1 or E1), CDKs (1, 2, 4 or 6), and the p21 ^Cip1 inhibitor, in a DUSP3-dependent manner. DUSP3 lof affected the proliferation of MRC-5 and XPA cells, with marked worsening of the XP phenotype after UV radiation. This work highlights the roles of DUSP3 in DNA repair fitness and in the fine control of regulatory proteins of cell cycle, essential mechanisms to maintenance of genomic stability.

Dual-Specificity Phosphatases in Neuroblastoma Cell Growth and Differentiation

Dual-specificity phosphatases (DUSPs) are important regulators of neuronal cell growth and differentiation by targeting proteins essential to neuronal survival in signaling pathways, among which the MAP kinases (MAPKs) stand out. DUSPs include the MAPK phosphatases (MKPs), a family of enzymes that directly dephosphorylate MAPKs, as well as the small-size atypical DUSPs, a group of low molecular-weight enzymes which display more heterogeneous substrate specificity. Neuroblastoma (NB) is a malignancy intimately associated with the course of neuronal and neuroendocrine cell differentiation, and constitutes the source of more common extracranial solid pediatric tumors. Here, we review the current knowledge on the involvement of MKPs and small-size atypical DUSPs in NB cell growth and differentiation, and discuss the potential of DUSPs as predictive biomarkers and therapeutic targets in human NB.