Dual-specificity phosphatase 26 protects against kidney injury caused by ischaemia-reperfusion through restraint of TAK1-JNK/p38-mediated apoptosis and inflammation of renal tubular epithelial cells

Dual-specificity phosphatase 26 (DUSP26) acts as a pivotal player in the transduction of signalling cascades with its dephosphorylating activity. Currently, DUSP26 attracts extensive attention due to its particular function in several pathological conditions. However, whether DUSP26 plays a role in kidney ischaemia-reperfusion (IR) injury is unknown. Aims of the current work were to explore the relevance of DUSP26 in kidney IR damage. DUSP26 levels were found to be decreased in renal tubular epithelial cells following hypoxia-reoxygenation (HR) and kidney samples subjected to IR treatments. DUSP26-overexpressed renal tubular epithelial cells exhibited protection against HR-caused apoptosis and inflammation, while DUSP26-depleted renal tubular epithelial cells were more sensitive to HR damage. Upregulation of DUSP26 in rat kidneys by infecting adenovirus expressing DUSP26 markedly ameliorated kidney injury caused by IR, while also effectively reducing apoptosis and inflammation. The mechanistic studies showed that the activation of transforming growth factor-β-activated kinase 1 (TAK1)-JNK/p38 MAPK, contributing to kidney injury under HR or IR conditions, was restrained by increasing DUSP26 expression. Pharmacological restraint of TAK1 markedly diminished DUSP26-depletion-exacebated effects on JNK/p38 activation and HR injury of renal tubular cells. The work reported a renal-protective function of DUSP26, which protects against IR-related kidney damage via the intervention effects on the TAK1-JNK/p38 axis. The findings laid a foundation for understanding the molecular pathogenesis of kidney IR injury and provide a prospective target for treating this condition.

Upregulation of dual-specificity phosphatase-26 is required for transforming growth factor β1(TGFβ1)-induced Epithelial-mesenchymal transition in A549 and PANC1 cells

BACKGROUND

Transforming Growth Factor β (TGFβ) proteins are potent inducers of the epithelial-mesenchymal transition (EMT) in tumor cells. Although mitogen-activated protein kinase (MAPK) family has been shown to be involved in TGFβ-induced EMT, role of Dual Specificity Phosphatases (DUSP), key regulators of MAPK activity, in TGFβ-induced EMT is largely unkonwn.

METHODS AND RESULTS

Real-time qPCR analyses were performed to determine the effect of TGFβ1 on expression of EMT genes and DUSP proteins in the non-small cell lung cancer model A549 and pancreatic adenocarcinoma model PANC1 cells. Western blot analyses were conducted to study the changes in protein levels of EMT proteins and select DUSP proteins, as well as phosphorylations of MAPK proteins upon TGFβ1 stimulation. Small interfering RNA (siRNA) was utilized to reduce expressions of DUSP genes. We observed that the EMT phenotype coincided with increases in phosphorylations of the MAPK proteins ERK1/2, p38MAPK, and JNK upon TGFβ1 stimulation. Real-time qPCR analysis showed increases in DUSP15 and DUSP26 mRNA levels and Western blot analysis confirmed the increase in DUSP26 protein levels in both A549 and PANC1 cells treated with TGFβ1 relative to control. Silencing of DUSP26 expression by siRNA markedly suppressed the effect of TGFβ1 on E-cadherin and mesenchymal genes in the cells.

CONCLUSIONS

Data provided suggest that TGFβ1 modulates the expression of DUSP genes and that upregulation of DUSP26 may be required for TGFβ1-promoted EMT in A549 and PANC1 cells. Further studies should be carried out to elucidate the requirement of individual DUSPs in TGFβ1-associated EMT in tumor cells.

Falnidamol and cisplatin combinational treatment inhibits non-small cell lung cancer (NSCLC) by targeting DUSP26-mediated signal pathways

Non-small-cell lung cancer (NSCLC) is one of the most commonly diagnosed cancers worldwide with limited effective therapies. Cisplatin (DDP), as the first-line treatment, is always served as a mainstay of chemotherapeutic agents in combination with other drugs for NSCLC treatment. Nevertheless, DDP-based therapy is limited due to the frequent development of chemoresistance and adverse effects. Herein, it is necessary to find a more effective therapeutic approach with less toxicity. Falnidamol (FLD) is a pyrimido-pyrimidine compound and exerts anti-cancer activity. In the present study, we found that FLD could strongly promote the cytotoxicity of DDP and markedly reduce the IC₅₀ values to restrain the proliferation of NSCLC cells. Furthermore, combination of FLD and DDP remarkably induced G2/M cell cycle arrest, DNA damage and mitochondrial apoptosis, which was largely through the induction of reactive oxygen species (ROS). Additionally, FLD/DDP in combination greatly triggered ferroptosis, along with free iron accumulation and enhanced lipid peroxidation. Epithelial to mesenchymal transition (EMT) and epidermal growth factor receptor (EGFR) phosphorylation were also considerably restrained in NSCLC cells co-treated with FLD/DDP. Mechanistically, the combinative treatment significantly reduced DUSP26 expression in NSCLC cells. More studies showed that DUSP26 was strongly up-regulated in human NSCLC samples compared with the paired normal tissues, and high DUSP26 predicted poor overall survival rate among patients. Importantly, we found that DUSP26 suppression intensively reduced the proliferation, EMT process and pEGFR expression in NSCLC cells, whereas facilitated ROS production, DNA damage and cell death; however, opposite phenotype was observed in NSCLC cells over-expressing DUSP26. More importantly, DUSP26 over-expression completely abolished the anti-cancer function of FLD/DDP in NSCLC cells. Animal studies finally confirmed that FLD/DDP in combination efficiently reduced tumor growth and lung metastasis in mice with ameliorated side effects. In conclusion, all these data illustrated that FLD and DDP combinational treatment effectively restrained NSCLC progression, and thus can be served as a promising therapeutic strategy.

Dual-Specificity Phosphatase 26 Protects Against Cardiac Hypertrophy Through TAK1

Background Heart pathological hypertrophy has been recognized as a predisposing risk factor for heart failure and arrhythmia. DUSP (dual-specificity phosphatase) 26 is a member of the DUSP family of proteins, which has a significant effect on nonalcoholic fatty liver disease, neuroblastoma, glioma, and so on. However, the involvement of DUSP26 in cardiac hypertrophy remains unclear. Methods and Results Our study showed that DUSP26 expression was significantly increased in mouse hearts in response to pressure overload as well as in angiotensin II-treated cardiomyocytes. Cardiac-specific overexpression of DUSP26 mice showed attenuated cardiac hypertrophy and fibrosis, while deficiency of DUSP26 in mouse hearts resulted in increased cardiac hypertrophy and deteriorated cardiac function. Similar effects were also observed in cellular hypertrophy induced by angiotensin II. Importantly, we showed that DUSP26 bound to transforming growth factor-β activated kinase 1 and inhibited transforming growth factor-β activated kinase 1 phosphorylation, which led to suppression of the mitogen-activated protein kinase signaling pathway. In addition, transforming growth factor-β activated kinase 1-specific inhibitor inhibited cardiomyocyte hypertrophy induced by angiotensin II and attenuated the exaggerated hypertrophic response in DUSP26 conditional knockout mice. Conclusions Taken together, DUSP26 was induced in cardiac hypertrophy and protected against pressure overload induced cardiac hypertrophy by modulating transforming growth factor-β activated kinase 1-p38/ c-Jun N-terminal kinase-signaling axis. Therefore, DUSP26 may provide a therapeutic target for treatment of cardiac hypertrophy and heart failure.

DUSP26 regulates podocyte oxidative stress and fibrosis in a mouse model with diabetic nephropathy through the mediation of ROS

Diabetic nephropathy (DN) is a leading cause of renal failure worldwide. Unfortunately, the pathogenetic mechanism of DN is far from to be understood. Dual-specificity phosphatase 26 (DUSP26) is a member of the Dusp protein family, and is suggested to be involved in divers biological and pathological processes, such as cell growth, differentiation, inflammation and apoptosis. However, its role in the development of DN is still vague. In this study, we found that DUSP26 expression was increased in kidney of DN patients. Then, the wild type (DUSP26^+/+) and gene knockout (DUSP26^-/-) mice were used to further explore the effects of DUSP26 on DN development induced by streptozotocin (STZ). DUSP26 deficiency accelerated renal injury and dysfunction, as evidenced by the elevated glomerulosclerosis, reduced expression of Nephrin and promoted glomerular basement membrane thickness. In addition, STZ treatment resulted in reactive oxygen species (ROS) accumulation, H₂O₂ overproduction and superoxide dismutase (SOD) reduction in renal cortex or glomeruli of mice. The ROS production caused the activation of mitogen-activated protein kinase (MAPKs) signaling in kidney glomeruli of STZ-induced mice. These in vivo pathological processes were further confirmed in the differentiated podocytes stimulated by glucose (GLU). Intriguingly, we found that STZ-induced DN as mentioned above was further accelerated by DUSP26^-/- in mice following STZ injection. Moreover, STZ-induced fibrosis in kidney glomeruli of DN mice was markedly prolonged in DUSP26-knockout mice through potentiating transforming growth factor-β1 (TGF-β1) expression. More importantly, reducing ROS generation could significantly abolish DUSP26 knockdown-exacerbated TGF-β1 expression and MAPKs activation, thereby protecting podocytes from GLU-induced podocyte injury. Thus, DUSP26-regulated DN development was largely dependent on ROS generation. Taken together, we concluded that DUSP26 might be a promising therapeutic target for developing effective treatments against DN progression.

Identification of novel dual-specificity phosphatase 26 inhibitors by a hybrid virtual screening approach based on pharmacophore and molecular docking

Dual-specificity phosphatase 26 (DUSP26) has recently emerged as a target for treatment of human cancers. However, only two small-molecule inhibitors of DUSP26 are known so far, namely NSC-87877 and ethyl-3, 4-dephostatin. DUSP26 contains an N-terminal region (residues 1-60) and a conserved C-terminal catalytic domain (residues 61-211, DUSP26-C). The crystal structure of DUSP26-C, showing a catalytically inactive conformation of the active site, was reported in a previous study. However, the detailed catalytic mechanism of DUSP26 cannot be described based on that structure. In this study, the 3D structure of DUSP26 (residues 42-211) adopting catalytically active conformation, was built by homology modeling, and the established 3D structure was validated using enzyme kinetic assays. Pharmacophore modeling based on the validated 3D structure of human DUSP26 was carried out. The established pharmacophore model was considered as a 3D query for retrieving novel DUSP26 inhibitors from the chemical databases "Diversity Libraries" (129,087 compounds). Next, a docking study was performed to refine the obtained hit compounds. Then a total of 100 compounds were selected based on the ranking order and visual examination, which were then evaluated by an enzyme-based assay. Eight compounds were found to have inhibitory activities against DUSP26, and the most potent compound was assigned No. F1063-0967 with an IC₅₀ value of 11.62μM. The inhibitory activity of F1063-0967 against DUSP26 is higher than that of NCS87877 (IC₅₀ value: 16.67±2.89μM), but lower than that of ethyl-3, 4-dephostatin (IC₅₀ value: 6.8±0.41μM). MTT assay results revealed that F1063-0967 can induce apoptosis in IMR-32 cell line with an IC₅₀ value of 4.13μM. These results suggest that F1063-0967 should be investigated further for other pharmacological properties.

Comprehensive protein tyrosine phosphatase mRNA profiling identifies new regulators in the progression of glioma

The infiltrative behavior of diffuse gliomas severely reduces therapeutic potential of surgical resection and radiotherapy, and urges for the identification of new drug-targets affecting glioma growth and migration. To address the potential role of protein tyrosine phosphatases (PTPs), we performed mRNA expression profiling for 91 of the 109 known human PTP genes on a series of clinical diffuse glioma samples of different grades and compared our findings with in silico knowledge from REMBRANDT and TCGA databases. Overall PTP family expression levels appeared independent of characteristic genetic aberrations associated with lower grade or high grade gliomas. Notably, seven PTP genes (DUSP26, MTMR4, PTEN, PTPRM, PTPRN2, PTPRT and PTPRZ1) were differentially expressed between grade II-III gliomas and (grade IV) glioblastomas. For DUSP26, PTEN, PTPRM and PTPRT, lower expression levels correlated with poor prognosis, and overexpression of DUSP26 or PTPRT in E98 glioblastoma cells reduced tumorigenicity. Our study represents the first in-depth analysis of PTP family expression in diffuse glioma subtypes and warrants further investigations into PTP-dependent signaling events as new entry points for improved therapy.

Dual-specificity phosphatase 26 (DUSP26) stimulates Aβ42 generation by promoting amyloid precursor protein axonal transport during hypoxia

Amyloid beta peptide (Aβ) is a pathological hallmark of Alzheimer's disease (AD) and is generated through the sequential cleavage of amyloid precursor protein (APP) by β- and γ-secretases. Hypoxia is a known risk factor for AD and stimulates Aβ generation by γ-secretase; however, the underlying mechanisms remain unclear. In this study, we showed that dual-specificity phosphatase 26 (DUSP26) regulates Aβ generation through changes in subcellular localization of the γ-secretase complex and its substrate C99 under hypoxic conditions. DUSP26 was identified as a novel γ-secretase regulator from a genome-wide functional screen using a cDNA expression library. The phosphatase activity of DUSP26 was required for the increase in Aβ42 generation through γ-secretase, but this regulation did not affect the amount of the γ-secretase complex. Interestingly, DUSP26 induced the accumulation of C99 in the axons by stimulating anterograde transport of C99-positive vesicles. Additionally, DUSP26 induced c-Jun N-terminal kinase (JNK) activation for APP processing and axonal transport of C99. Under hypoxic conditions, DUSP26 expression levels were elevated together with JNK activation, and treatment with JNK inhibitor SP600125, or the DUSP26 inhibitor NSC-87877, reduced hypoxia-induced Aβ generation by diminishing vesicle trafficking of C99 to the axons. Finally, we observed enhanced DUSP26 expression and JNK activation in the hippocampus of AD patients. Our results suggest that DUSP26 mediates hypoxia-induced Aβ generation through JNK activation, revealing a new regulator of γ-secretase-mediated APP processing under hypoxic conditions. We propose the role of phosphatase dual-specificity phosphatase 26 (DUSP26) in the selective regulation of Aβ42 production in neuronal cells under hypoxic stress. Induction of DUSP26 causes JNK-dependent shift in the subcellular localization of γ-secretase and C99 from the cell body to axons for Aβ42 generation. These findings provide a new strategy for developing new therapeutic targets to arrest AD progression.

VHR/DUSP3 phosphatase: structure, function and regulation

Vaccinia H1-related (VHR) phosphatase, also known as dual-specificity phosphatase (DUSP) 3, is a small member of the DUSP (also called DSP) family of phosphatases. VHR has a preference for phospho-tyrosine substrates, and has important roles in cellular signaling ranging from cell-cycle regulation and the DNA damage response to MAPK signaling, platelet activation and angiogenesis. VHR/DUSP3 has been implicated in several human cancers, where its tumor-suppressing and -promoting properties have been described. We give a detailed overview of VHR/DUSP3 phosphatase and compare it with its most closely related phosphatases DUSP13B, DUSP26 and DUSP27.

High-resolution crystal structure of the catalytic domain of human dual-specificity phosphatase 26

Dual-specificity phosphatases (DUSPs) play an important role in regulating cellular signalling pathways governing cell growth, differentiation and apoptosis. Human DUSP26 inhibits the apoptosis of cancer cells by dephosphorylating substrates such as p38 and p53. High-resolution crystal structures of the DUSP26 catalytic domain (DUSP26-C) and its C152S mutant [DUSP26-C (C152S)] have been determined at 1.67 and 2.20 Å resolution, respectively. The structure of DUSP26-C showed a novel type of domain-swapped dimer formed by extensive crossover of the C-terminal α7 helix. Taken together with the results of a phosphatase-activity assay, structural comparison with other DUSPs revealed that DUSP26-C adopts a catalytically inactive conformation of the protein tyrosine phosphate-binding loop which significantly deviates from that of canonical DUSP structures. In particular, a noticeable difference exists between DUSP26-C and the active forms of other DUSPs at the hinge region of a swapped C-terminal domain. Additionally, two significant gaps were identified between the catalytic core and its surrounding loops in DUSP26-C, which can be exploited as additional binding sites for allosteric enzyme regulation. The high-resolution structure of DUSP26-C may thus provide structural insights into the rational design of DUSP26-targeted anticancer drugs.