The crystal structure of C. elegans Ap(4)A hydrolase has been determined for the free enzyme and a binary complex at 2.0 A and 1.8 A, respectively. Ap(4)A hydrolase has a key role in regulating the intracellular Ap(4)A levels and hence potentially the cellular response to metabolic stress and/or differentiation and apoptosis via the Ap(3)A/Ap(4)A ratio. The structures reveal that the enzyme has the mixed alpha/beta fold of the Nudix family and also show how the enzyme binds and locates its substrate with respect to the catalytic machinery of the Nudix motif. These results suggest how the enzyme can catalyze the hydrolysis of a range of related dinucleoside tetraphosphate, but not triphosphate, compounds through precise orientation of key elements of the substrate.

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Hepatocyte growth factor (HGF) gene transfer inhibits liver fibrosis by regulating aberrant cellular functions, while mutant matrix metalloproteinase-9 (mMMP-9) enhances matrix degradation by neutralizing the elevated tissue inhibitor of metalloproteinase-1 (TIMP-1). It was shown that ASH1 and EZH2 methyltransferases are involved in development of liver fibrosis; however, their role in the resolution phase of liver fibrosis has not been investigated. This study evaluated the role of ASH1 and EZH2 in two mechanistically different therapeutic modalities, HGF and mMMP-9 gene transfer in CCl4 induced rat liver fibrosis. Liver fibrosis was induced in rats with twice a week intraperitoneal injection of CCl4 for 8 weeks. Adenovirus vectors encoding mMMP-9 or HGF genes were injected through tail vein at weeks six and seven and were sacrificed one week after the second injection. A healthy animal group was likewise injected with saline to serve as a negative control. Rats treated with mMMP-9 showed significantly lower fibrosis score, less Sirius red stained collagen area, reduced hydroxyproline and ALT concentration, decreased transforming growth factor beta 1 (TGF-β1) mRNA and lower labeling indices of α smooth muscle actin (α-SMA) and proliferating cell nuclear antigen (PCNA) stained cells compared with HGF- or saline-treated rats. Furthermore, TIMP-1 protein expression in mMMP-9 group was markedly reduced compared with all fibrotic groups. ASH1 and EZH2 protein expression was significantly elevated in fibrotic liver and significantly decreased in mMMP-9- and HGF-treated compared to saline-treated fibrotic livers with further reduction in the mMMP-9 group. Conclusion: Gene transfer of mMMP-9 and HGF reduced liver fibrosis in rats. ASH1 and EZH2 methyltransferases are significantly reduced in mMMP-9 and HGF treated rats which underlines the central role of these enzymes during fibrogenesis. Future studies should evaluate the role of selective pharmacologic inhibitors of ASH1 and EZH2 in resolution of liver fibrosis.

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Liver fibrosis is an excessively reversible wound healing process and the fibrotic disorder is the activation of hepatic stellate cell that requires extensive alterations in gene expression. As reversible deacetylation of histone proteins modulate gene expression, we examined the effect of valproic acid (VPA) as selective histone deacetylase inhibitor on CCl-4 induced liver fibrosis. Thirty rats were divided into three equal groups; control group, fibrotic group and VPA-treated group. The rats were sacrificed after 6 weeks of liver fibrosis induction. The histopathological effect on liver tissue was examined. The expression of α-SMA and Smad-4 mRNA and serum levels of TGF-β1, alanine aminotransferase, and aspartate aminotransferase were determined. Treatment of rats with VPA attenuated carbon tetrachloride-induced liver fibrosis. Moreover, α-SMA and Smad-4 expression was repressed under VPA treatment and both serum TGF-β1 and liver enzymes were significantly decreased. The histone deacetylase inhibitor-1 VPA inhibits the epithelial-mesenchymal transition and affects hepatic stellate cell activation during liver fibrosis through downregulation of Smad4 and α-SMA expression which may serve as a promising agent in liver fibrosis treatment. © 2018 IUBMB Life, 70(6):511-518, 2018.