Identification of inhibitors that target dual-specificity phosphatase 5 provide new insights into the binding requirements for the two phosphate pockets

Enhanced Cerebral Hemodynamics and Cognitive Function Via Knockout of Dual-Specificity Protein Phosphatase 5

Alzheimer's Disease (AD) and Alzheimer's Disease-Related Dementias (ADRD) are neurodegenerative disorders. Recent studies suggest that cerebral hypoperfusion is an early symptom of AD/ADRD. Dual-specificity protein phosphatase 5 (DUSP5) has been implicated in several pathological conditions, including pulmonary hypertension and cancer, but its role in AD/ADRD remains unclear. The present study builds on our previous findings, demonstrating that inhibition of ERK and PKC leads to a dose-dependent dilation of the middle cerebral artery and penetrating arteriole, with a more pronounced effect in Dusp5 KO rats. Both ERK and PKC inhibitors resulted in a significant reduction of myogenic tone in vessels from Dusp5 KO rats. Dusp5 KO rats exhibited stronger autoregulation of the surface but not deep cortical cerebral blood flow. Inhibition of ERK and PKC significantly enhanced the contractile capacity of vascular smooth muscle cells from both strains. Finally, a significant improvement in learning and memory was observed in Dusp5 KO rats 24 hours after initial training. Our results suggest that altered vascular reactivity in Dusp5 KO rats may involve distinct mechanisms for different vascular beds, and DUSP5 deletion could be a potential therapeutic target for AD/ADRD. Further investigations are necessary to determine the effects of DUSP5 inhibition on capillary stalling, blood-brain barrier permeability, and neurodegeneration in aging and disease models.

Efficient Protocol for Expression and Purification of DUSP5

Dual Specificity Phosphatase 5 (DUSP5) is a human protein that targets specific kinases and dephosphorylates phosphoserine/threonine and phosphotyrosine residues. DUSP5 is found to be involved in cardiovascular diseases and many cancer pathways, including skin and breast cancer. For this reason, availability of an efficient protocol of expression and purification of DUSP proteins can play a crucial role in their studies towards better understanding of the disease process and development of better therapeutic approaches. For example, purification of DUSP5 could be used for the in vitro assays of the inhibitors of DUSP5 identified from the in-silico studies. This report provides the full procedure for protein purification thereby allowing the collection of desired amounts of DUSP5 using Glutathione S-transferase (GST) tag. The described method shows an efficient way to solubilize and purify DUSP5 for further protein studies.

Dual specific phosphatases (DUSPs) in cardiac hypertrophy and failure

Pressure overload and other stress stimuli elicit a host of adaptive and maladaptive signaling cascades that eventually lead to cardiac hypertrophy and heart failure. Among those, the mitogen-activated protein kinase (MAPK) signaling pathway has been shown to play a prominent role. The dual specificity phosphatases (DUSPs), also known as MAPK specific phosphatases (MKPs), that can dephosphorylate the MAPKs and inactivate them are gaining increasing attention as potential drug targets. Here we try to review recent advancements in understanding the roles of the different DUSPs, and the pathways that they regulate in cardiac remodeling. We focus on the regulation of three main MAPK branches - the p38 kinases, the c-Jun-N-terminal kinases (JNKs) and the extracellular signal-regulated kinases (ERK) by various DUSPs and try to examine their roles.

Knockout of Dual-Specificity Protein Phosphatase 5 Protects Against Hypertension-Induced Renal Injury

Dual-specificity protein phosphatase 5 (DUSP5) is a member of the tyrosine-threonine phosphatase family with the ability to dephosphorylate and inactivate extracellular signal-related kinase (ERK). The present study investigates whether knockout (KO) of Dusp5 improves renal hemodynamics and protects against hypertension-induced renal injury. The renal expression of DUSP5 was reduced, and the levels of phosphorylated (p) ERK1/2 and p-protein kinase C (PKC) α were elevated in the KO rats. KO of Dusp5 enhanced the myogenic tone of the renal afferent arteriole and interlobular artery in vitro with or without induction of deoxycorticosterone acetate-salt hypertension. Inhibition of ERK1/2 and PKC diminished the myogenic response to a greater extent in Dusp5 KO rats. Autoregulation of renal blood flow was significantly impaired in hypertensive wild-type (WT) rats but remained intact in Dusp5 KO animals. Proteinuria was markedly decreased in hypertensive KO versus WT rats. The degree of glomerular injury was reduced, and the expression of nephrin in the glomerulus was higher in hypertensive Dusp5 KO rats. Renal fibrosis and medullary protein cast formation were attenuated in hypertensive Dusp5 KO rats in association with decreased expression of monocyte chemoattractant protein 1, transforming growth factor-β1, matrix metalloproteinase (MMP) 2, and MMP9. These results indicate that KO of Dusp5 protects against hypertension-induced renal injury, at least in part, by maintaining the myogenic tone of the renal vasculature and extending the range of renal blood flow autoregulation to higher pressures, which diminish glomerular injury, protein cast formation, macrophage infiltration, and epithelial-mesenchymal transformation in the kidney. SIGNIFICANCE STATEMENT: Dual-specificity protein phosphatase 5 (DUSP5) is a tyrosine-threonine phosphatase that inactivates extracellular signal-related kinase (ERK). We previously reported that knockout (KO) of Dusp5 enhanced the myogenic response and autoregulation in the cerebral circulation. The present study investigates whether KO of DUSP5 improves renal hemodynamics and protects against hypertension-induced renal injury. Downregulation of DUSP5 enhanced the myogenic tone of renal arteriole and artery and autoregulation of renal blood flow in association with reduced proteinuria, glomerular injury, and interstitial fibrosis after the induction of hypertension. Inhibition of ERK1/2 and protein kinase C diminished the myogenic response to a greater extent in Dusp5 KO rats. These results suggest that DUSP5 might be a viable drug target for the treatment of hypertension nephropathy.

Role of Conserved Histidine and Serine in the HCXXXXXRS Motif of Human Dual-Specificity Phosphatase 5

BACKGROUND

The mitogen-activated protein kinase (MAPK) pathway is functionally generic and critical in maintaining physiological homeostasis and normal tissue development. This pathway is under tight regulation, which is in part mediated by dual-specific phosphatases (DUSPs), which dephosphorylate serine, threonine, and tyrosine residues of the ERK family of proteins. DUSP5 is of high clinical interest because of mutations we identified in this protein in patients with vascular anomalies. Unlike other DUSPs, DUSP5 has unique specificity toward substrate pERK1/2. Using molecular docking and simulation strategies, we previously showed that DUSP5 has two pockets, which are utilized in a specific fashion to facilitate specificity toward catalysis of its substrate pERK1/2. Remarkably, most DUSPs share high similarity in their catalytic sites. Studying the catalytic domain of DUSP5 and identifying amino acid residues that are important for dephosphorylating pERK1/2 could be critical in developing small molecules for therapies targeting DUSP5.

RESULTS

In this study, we utilized computational modeling to identify and predict the importance of two conserved amino acid residues, H262 and S270, in the DUSP5 catalytic site. Modeling studies predicted that catalytic activity of DUSP5 would be altered if these critical conserved residues were mutated. We next generated independent Glutathione-S-Transferase (GST)-tagged full-length DUSP5 mutant proteins carrying specific mutations H262F and S270A in the phosphatase domain. Biochemical analysis was performed on these purified proteins, and consistent with our computational prediction, we observed altered enzyme activity kinetic profiles for both mutants with a synthetic small molecule substrate (pNPP) and the physiological relevant substrate (pERK) when compared to wild type GST-DUSP5 protein.

CONCLUSION

Our molecular modeling and biochemical studies combined demonstrate that enzymatic activity of phosphatases can be manipulated by mutating specific conserved amino acid residues in the catalytic site (phosphatase domain). This strategy could facilitate generation of small molecules that will serve as agonists/antagonists of DUSP5 activity.

Discovery and Characterization of Halogenated Xanthene Inhibitors of DUSP5 as Potential Photodynamic Therapeutics

Dual specific phosphatases (DUSPs) are an important class of mitogen-activated protein kinase (MAPK) regulators, and are drug targets for treating vascular diseases. Previously we had shown that DUSP5 plays a role in embryonic vertebrate vascular patterning. Herein, we screened a library of FDA-approved drugs and related compounds, using a para-nitrophenylphosphate substrate (pNPP)-based assay. This assay identified merbromin (also known as mercurochrome) as targeting DUSP5; and, we subsequently identified xanthene-ring based merbromin analogs eosin Y, erythrosin B, and rose bengal, all of which inhibit DUSP5 in vitro. Inhibition was time-dependent for merbromin, eosin Y, 2',7'-dibromofluorescein, and 2',7'-dichlorofluorescein, with enzyme inhibition increasing over time. Reaction progress curve data fit best to a slow-binding model of irreversible enzyme inactivation. Potency of the time-dependent compounds, except for 2',7'-dichlorofluorescein, was diminished when dithiothreitol (DTT) was present, suggesting thiol reactivity. Two additional merbromin analogs, erythrosin B and rose bengal also inhibit DUSP5, but have the therapeutic advantage of being less sensitive to DTT and exhibiting little time dependence for inhibition. Inhibition potency is correlated with the xanthene dye's LUMO energy, which affects ability to form light-activated radical anions, a likely active inhibitor form. Consistent with this hypothesis, rose bengal inhibition is light-dependent and demonstrates the expected red shifted spectrum upon binding to DUSP5, with a Kd of 690 nM. These studies provide a mechanistic foundation for further development of xanthene dyes for treating vascular diseases that respond to DUSP5 inhibition, with the following relative potencies: rose bengal > merbromin > erythrosin B > eosin Y.

Critical Roles of Dual-Specificity Phosphatases in Neuronal Proteostasis and Neurological Diseases

Protein homeostasis or proteostasis is a fundamental cellular property that encompasses the dynamic balancing of processes in the proteostasis network (PN). Such processes include protein synthesis, folding, and degradation in both non-stressed and stressful conditions. The role of the PN in neurodegenerative disease is well-documented, where it is known to respond to changes in protein folding states or toxic gain-of-function protein aggregation. Dual-specificity phosphatases have recently emerged as important participants in maintaining balance within the PN, acting through modulation of cellular signaling pathways that are involved in neurodegeneration. In this review, we will summarize recent findings describing the roles of dual-specificity phosphatases in neurodegeneration and offer perspectives on future therapeutic directions.

Dual Specificity Phosphatase 5-Substrate Interaction: A Mechanistic Perspective

The mammalian genome contains approximately 200 phosphatases that are responsible for catalytically removing phosphate groups from proteins. In this review, we discuss dual specificity phosphatase 5 (DUSP5). DUSP5 belongs to the dual specificity phosphatase (DUSP) family, so named after the family members' abilities to remove phosphate groups from serine/threonine and tyrosine residues. We provide a comparison of DUSP5's structure to other DUSPs and, using molecular modeling studies, provide an explanation for DUSP5's mechanistic interaction and specificity toward phospho-extracellular regulated kinase, its only known substrate. We also discuss new insights from molecular modeling studies that will influence our current thinking of mitogen-activated protein kinase signaling. Finally, we discuss the lessons learned from identifying small molecules that target DUSP5, which might benefit targeting efforts for other phosphatases. © 2017 American Physiological Society. Compr Physiol 7:1449-1461, 2017.

Serendipitous discovery of light-induced (In Situ) formation of an Azo-bridged dimeric sulfonated naphthol as a potent PTP1B inhibitor

BACKGROUND

Protein tyrosine phosphatases (PTPs) like dual specificity phosphatase 5 (DUSP5) and protein tyrosine phosphatase 1B (PTP1B) are drug targets for diseases that include cancer, diabetes, and vascular disorders such as hemangiomas. The PTPs are also known to be notoriously difficult targets for designing inihibitors that become viable drug leads. Therefore, the pipeline for approved drugs in this class is minimal. Furthermore, drug screening for targets like PTPs often produce false positive and false negative results.

RESULTS

Studies presented herein provide important insights into: (a) how to detect such artifacts, (b) the importance of compound re-synthesis and verification, and (c) how in situ chemical reactivity of compounds, when diagnosed and characterized, can actually lead to serendipitous discovery of valuable new lead molecules. Initial docking of compounds from the National Cancer Institute (NCI), followed by experimental testing in enzyme inhibition assays, identified an inhibitor of DUSP5. Subsequent control experiments revealed that this compound demonstrated time-dependent inhibition, and also a time-dependent change in color of the inhibitor that correlated with potency of inhibition. In addition, the compound activity varied depending on vendor source. We hypothesized, and then confirmed by synthesis of the compound, that the actual inhibitor of DUSP5 was a dimeric form of the original inhibitor compound, formed upon exposure to light and oxygen. This compound has an IC50 of 36 μM for DUSP5, and is a competitive inhibitor. Testing against PTP1B, for selectivity, demonstrated the dimeric compound was actually a more potent inhibitor of PTP1B, with an IC50 of 2.1 μM. The compound, an azo-bridged dimer of sulfonated naphthol rings, resembles previously reported PTP inhibitors, but with 18-fold selectivity for PTP1B versus DUSP5.

CONCLUSION

We report the identification of a potent PTP1B inhibitor that was initially identified in a screen for DUSP5, implying common mechanism of inhibitory action for these scaffolds.