ACTH Modulates PTP‐PEST Activity and Promotes Its Interaction With Paxillin

Adrenocorticotropic hormone (ACTH) treatment has been proven to promote paxillin dephosphorylation and increase soluble protein tyrosine phosphatase (PTP) activity in rat adrenal zona fasciculata (ZF). Also, in‐gel PTP assays have shown the activation of a 115‐kDa PTP (PTP115) by ACTH. In this context, the current work presents evidence that PTP115 is PTP‐PEST, a PTP that recognizes paxillin as substrate. PTP115 was partially purified from rat adrenal ZF and PTP‐PEST was detected through Western blot in bioactive samples taken in each purification step. Immunohistochemical and RT‐PCR studies revealed PTP‐PEST expression in rat ZF and Y1 adrenocortical cells. Moreover, a PTP‐PEST siRNA decreased the expression of this phosphatase. PKA phosphorylation of purified PTP115 isolated from non‐ACTH‐treated rats increased K_M and V_M. Finally, in‐gel PTP assays of immunoprecipitated paxillin from control and ACTH‐treated rats suggested a hormone‐mediated increase in paxillin–PTP115 interaction, while PTP‐PEST and paxillin co‐localize in Y1 cells. Taken together, these data demonstrate PTP‐PEST expression in adrenal ZF and its regulation by ACTH/PKA and also suggest an ACTH‐induced PTP–PEST–paxillin interaction. J. Cell. Biochem. 117: 2170–2181, 2016. © 2016 The Authors. Journal of Cellular Biochemistry Published by Wiley Periodicals, Inc.     

Methylation of the PTPRO gene in human hepatocellular carcinoma and identification of VCP as its substrate

We have previously reported that the gene encoding protein tyrosine phosphatase receptor type‐O (PTPRO) is suppressed by promoter methylation in a rat model of hepatocellular carcinoma (HCC) and it functions as tumor suppressor in leukemia and lung cancer. Here, we explored the methylation and expression of PTPRO as well as its function in human HCC. MassARRAY analysis of primary human HCC and matching liver samples (n = 24) revealed significantly higher (P = 0.004) methylation density at the promoter CGI in tumors. Combined bisulfite restriction analysis (COBRA) of another set of human HCC samples (n = 17) demonstrated that the CGI was methylated in 29% of tumors where expression of PTPRO was lower than that in corresponding matching livers. A substrate‐trapping mutant of PTPRO that stabilizes the bound substrates was used to identify its novel substrate(s). VCP/p97 was found to be a PTPRO substrate by mass spectrometry of the peptides pulled down by the substrate‐trapping mutant of PTPRO. Tyrosyl dephosphorylation of VCP following ectopic expression of wild‐type PTPRO in H293T and HepG2 cells confirmed that it is a bona fide substrate of PTPRO. Treatment of PTPRO overexpressing HepG2 cells with Doxorubicin, a DNA damaging drug commonly used in therapy of primary HCC, sensitized these cells to this potent anticancer drug that correlated with dephosphorylation of VCP. Taken together, these results demonstrate methylation and downregulation of PTPRO in a subset of primary human HCC and establish VCP as a novel functionally important substrate of this tyrosine phosphatase that could be a potential molecular target for HCC therapy. J. Cell. Biochem. 114: 1810–1818, 2013. © 2013 Wiley Periodicals, Inc.     

Acid Phosphatase Polymorphism in European Shad (Fish: Clupeids)

Genetic polymorphism of acid phosphatases wasinvestigated in 11 populations of the two European Alosaspecies using isoelectric focusing after sampletreatment with neuraminidase. Two distinct loci, ACP1 and ACP2, were detected being ACP2 polymorphic.The observed genetic diversity between the species atthe ACP2 locus supports other studies which indicatethat A. alosa is the less polymorphic species of the two. This locus shows a higher geographicthan interspecific pattern of differentiation and theACP*2 allele is essentially confined to theMediterranean.     

Level of nitrated proteins in the plasma,platelets and liver of patients with liver cirrhosis

Abstract

Over-expression of nitric oxide synthase (NOS) and nitric oxide (NO) formation are associated with the pathogenesis of liver cirrhosis. NO-related stress alters the functions of biomolecules, especially proteins, probably as a result of nitration. The aim of this study was to assess the level of protein nitration and its correlation with the severity of the disease. Liver cirrhosis patients with different grades of severity (grades A, B, and C according to the Child–Pugh classification) were enrolled in this study. Nitroprotein content, arginine, citrulline, NO in terms of total nitrite, nitrosothiol (RSNO) and protein carbonyls were measured in blood. Immunohistochemical detection of nitroprotein was carried out in liver sections of cirrhosis patients. A significant elevation in the levels of serum and platelet arginine, arginase, citrulline, plasma, and platelet nitroproteins, RSNO, total nitrite, protein carbonyls and also a significant amount of nitrated proteins by immunohistochemical detection in tissue were observed in cirrhosis patients. The alterations were highly significant in grade C patients with bleeding complications when compared to those of grade B and A patients. In platelets, both cytosolic and cytoskeletal proteins were found to be nitrated significantly. The level of nitrite seems to have positive correlation with the level of nitroproteins in different grades of cirrhosis. The level of nitroproteins in plasma, platelets and liver tissue can be correlated with the severity of liver cirrhosis.     

Reactions of the melatonin metabolite N1-acetyl-5-methoxykynuramine (AMK) with the tyrosine side-chain fragment, 4-ethylphenol

Abstract

The melatonin metabolite N¹-acetyl-5-methoxykynuramine (AMK) has previously been shown to interact with various free radicals. Using the ABTS cation radical [ABTS = 2,2′-azino-bis-(3-ethylbenzthiazoline-6-sulfonic acid)] as an electron abstracting reactant, which does not destroy the aromate, we found that the reactive intermediate derived from AMK strongly interacts with the benzene rings of other AMK molecules to form di- and oligomers. Since oligomerization is rather unlikely at physiological concentrations, we investigated reactions with other putative reaction partners. The incubation of tyrosine or several of its structural analogs with AMK in the presence of the ABTS cation radical led to numerous products, amongst which were compounds not detected when one of the educts was incubated with the ABTS cation radical alone. With tyrosine and most of its analogs, the number of products formed in the presence of AMK and ABTS cation radical was relatively high and included numerous oligomers. To optimize the yield of products of interest as well as their separation from other compounds, especially oligomers, we investigated the interaction with 4-ethylphenol, which represents the side chain of tyrosine lacking the carboxyl and amino residues of the amino acid, which otherwise can undergo additional reactions. A prominent product was chromatographically separated and analyzed by mass spectrometry [(+)-ESI-MS, (?)-ESI-MS, (+)-HRESI-MS], ¹H-NMR, and H,H-COSY correlations. The substance was identified as N-{3-[2′-(5″-ethyl-2″-hydroxyphenylamino)-5′-methoxyphenyl]-3-oxopropyl} acetamide. This chemically novel compound represents an adduct in which the amino nitrogen of AMK is attached to the C-2 atom of 4-ethylphenol, which corresponds to the C-3 atom in the benzene ring of tyrosine. This finding suggests that, upon interaction of AMK with an electron-abstracting radical, the kynuric intermediate may modify proteins at superficially accessible tyrosine residues. In fact, protein modification by an unidentified melatonin metabolite has been observed in an earlier study. The possibility of protein AMKylation may be of interest with regard to an eventual interference with tyrosine nitration or, more importantly, with tyrosine phosphorylation.     

Zap70 inhibits Syk‐mediated osteoclast function

The αvβ3 integrin stimulates the resorptive capacity of the differentiated osteoclast (OC) by organizing its cytoskeleton via the tyrosine kinase, Syk. Thus, Syk‐deficient OCs fails to spread or form actin rings, in vitro and in vivo. The Syk family of tyrosine kinases consists of Syk itself and Zap70 which are expressed by different cell types. Because of their structural similarity, and its compensatory properties in other cells, we asked if Zap70 can substitute for absence of Syk in OCs. While expression of Syk, as expected, normalizes the cytoskeletal abnormalities of Syk^?/? OCs, Zap70 fails do so. In keeping with this observation, Syk, but not Zap70, rescues αvβ3 integrin‐induced SLP76 phosphorylation in Syk^?/? OCs. Furthermore the kinase sequence of Syk partially rescues the Syk^?/? phenotype but full normalization also requires its SH2 domains. Surprisingly, expression of Zap70 inhibits WT OC spreading, actin ring formation and bone resorptive activity, but not differentiation. In keeping with arrested cytoskeletal organization, Zap70 blocks integrin‐activated endogenous Syk and Vav3, SLP76 phosphorylation. Such inhibition requires Zap70 kinase activity, as it is abolished by mutation of the Zap70 kinase domain. Thus, while the kinase domain of Syk is uniquely required for OC function that of Zap70 inhibits it. J. Cell. Biochem. 114: 1871–1878, 2013. © 2013 Wiley Periodicals, Inc.     

Prophylactic role of Enhydra fluctuans against arsenic-induced hepatotoxicity via anti-apoptotic and antioxidant mechanisms

Abstract

Organisms produce reactive species throughout their lives, and this may result in damage to proteins and other biological molecules. Oxidatively damaged proteins are normally selectively degraded and replaced, but this process appears to be less efficient in senescent, long-lived, post-mitotic cells, as is evidenced by their accumulation in the form of lipofuscin inside the lysosomal compartment. A great deal of research has focused on changes to the proteolytic machinery in the ageing cell, in particular the proteasome, although failure of heat shock proteins (HSPs) to bind and deliver oxidised proteins efficiently to the degradation machinery could also contribute to their aggregation and accumulation. Oxidised proteins can be protease-resistant and may even directly inhibit the proteolytic machinery of the cell. The critical role that is played by HSPs in preventing accumulation of oxidised proteins is often overlooked. In this review, we examine the key role played by HSPs in recognising, removing and preventing the formation of oxidised and damaged proteins in cells. We also examine the evidence supporting the view that failure of one of these pathways could underlie ageing and age-related diseases. Finally, we discuss how modulation of HSP-activity could influence the ageing process and the progression of age-related diseases.