Biochemistry - Publicatons
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ItemSustainable Biocatalytic Synthesis of (S)-β-Nitro Alcohols using a Promiscuous (R)-Selective Hydroxynitrile Lyase(University of Hyderabad, 2021-12-24)
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ItemSirtuin 7 promotes cellular survival following genomic stress by attenuation of DNA damage, SAPK activation and p53 response( 2015-02-01)Maintaining the genomic integrity is a constant challenge in proliferating cells. Amongst various proteins involved in this process, Sirtuins play a key role in DNA damage repair mechanisms in yeast as well as mammals. In the present work we report the role of one of the least explored Sirtuin viz., SIRT7, under conditions of genomic stress when treated with doxorubicin. Knockdown of SIRT7 sensitized osteosarcoma (U2OS) cells to DNA damage induced cell death by doxorubicin. SIRT7 overexpression in NIH3T3 delayed cell cycle progression by causing delay in G1 to S transition. SIRT7 overexpressing cells when treated with low dose of doxorubicin (0.25. μM) showed delayed onset of senescence, lesser accumulation of DNA damage marker γH2AX and lowered levels of growth arrest markers viz., p53 and p21 when compared to doxorubicin treated control GFP expressing cells. Resistance to DNA damage following SIRT7 overexpression was also evident by EdU incorporation studies where cellular growth arrest was significantly delayed. When treated with higher dose of doxorubicin ( > 1. μM), SIRT7 conferred resistance to apoptosis by attenuating stress activated kinases (SAPK viz., p38 and JNK) and p53 response thereby shifting the cellular fate towards senescence. Interestingly, relocalization of SIRT7 from nucleolus to nucleoplasm together with its co-localization with SAPK was an important feature associated with DNA damage. SIRT7 mediated resistance to doxorubicin induced apoptosis and senescence was lost when p53 level was restored by nutlin treatment. Overall, we propose SIRT7 attenuates DNA damage, SAPK activation and p53 response thereby promoting cellular survival under conditions of genomic stress.
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ItemRole of cellular senescence in hepatic wound healing and carcinogenesis( 2012-10-01)A state of permanent growth arrest characterises a senescent cell. Both the beneficial and deleterious effects that have accrued in senescent cells are observed in a complex organ, such as the liver. Injury to liver tissues triggers processes of regeneration and associated wound healing. Persistent injury can also lead to the neoplastic state. Recent evidence linked the senescent characteristics of the cells to the beneficial processes of wound healing and tumour surveillance in the liver. On the other hand, the secretory phenotype of senescent cells can also selectively promote undesirable neoplastic progression. In an evolutionary context, a senescent cell can function primarily as an adaptive response featuring the characteristics of altruism, trade-offs and bystander effects. Using the liver cell as a model system, this review focuses on the current knowledge of the role of senescence in these seemingly contradictory cell phenomena. © 2012 Elsevier GmbH.
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ItemIntracellular distribution of human SIRT7 and mapping of the nuclear/nucleolar localization signal( 2013-07-01)Sirtuins belong to a class of NAD-dependent deacetylases, and include seven distinct isoforms, of which SIRT7 is the least studied member. In the present study, the subcellular expression of SIRT7 in primary fibroblasts undergoing senescence was evaluated by immunocytochemistry and immunoblot assay. Expression of nucleolar SIRT7 in young fibroblast was very prominent, decreased in pre-senescent cells, and became undetectable in the senescent cells. Interestingly, we observed previously unreported staining for cytoplasmic SIRT7 in fibroblasts, and report the existence of a steady-state level of SIRT7 in cytoplasm. Selective localization of the high-molecular-mass (47.5 kDa) SIRT7 in the cytoplasmic fraction and the low-molecular-mass (45 kDa) SIRT7 in the nuclear fraction was observed in the immunoblot analysis of various cell types. The specificity of the N-terminal antibodies for detection of cytoplasmic SIRT7 was confirmed by RNAi and peptide competition assays. The two forms of SIRT7 showed reciprocal expression following serum starvation, nocodazole and okadaic acid treatments, and also during senescence. Using a combination of deletion constructs and site-directed mutagenesis, we defined the role of two distinct SIRT7 sequences in the N-terminal region (amino acids 61-76, LQGRSRRREGLKRRQE) and the C-terminal region (amino acids 392-400, KRTKRKKVT) for nuclear and nucleolar import, respectively. In conclusion, we report for the first time the existence of a cytoplasmic pool of SIRT7 in addition to its well-known nucleolar form, identify distinct localization signals for its nuclear/nucleolar targeting, and describe an association between loss of nucleolar SIRT7 and replicative senescence. The subcellular expression of SIRT7 in fibroblasts and epithelial cells was evaluated. We now report existence of SIRT7 both in cytoplasm (47.5 kDa) and nucleolus (45 kDa). Loss of nucleolar SIRT7 was noted during replicative senescence. Additionally, we report the role of two distinct SIRT7 sequences in N-terminal (LQGRSRRREGLKRRQE) and C-terminal (KRTKRKKVT) regions for nuclear and nucleolar import, respectively. © 2013 FEBS.
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ItemExpression/localization patterns of sirtuins (SIRT1, SIRT2, and SIRT7) during progression of cervical cancer and effects of sirtuin inhibitors on growth of cervical cancer cells( 2015-08-24)Sirtuins belong to the family of class III histone deacetylases; its role in neoplasia is controversial as both tumor-suppressive and promoting functions have been reported. There are very few reports available, where expressions of sirtuin isoforms are comprehensively analyzed during neoplasia. Therefore, in the present study, the expression of SIRT1, SIRT2, and SIRT7 during different stages of cervical cancer progression was analyzed. The normal cervical epithelium showed feeble expression of sirtuin isoforms, SIRT1, SIRT2, and SIRT7. A significant increase in SIRT1 expression was noted in the cytoplasm as well as in the nucleus of proliferative layers of cervical epithelium in squamous intraepithelial lesions (SIL); however, in the squamous cell carcinomas (SCC), a heterogeneous pattern of SIRT1 expression varying from low to high was noted. A progressive increase in the expression of both SIRT2 and SIRT7 was noted during cancer progression in the following order: normal < preneoplasia < cancer. Cervical cancer cell lines, HeLa and SiHa, showed higher levels of SIRT1 and SIRT2 in comparison to the immortalized cell counterpart, HaCaT. Specific inhibitors of SIRT1 (Ex527) and SIRT2 (AGK2) impaired the growth of the cervical cancer cells, SiHa, but not of the HaCaT cells. SIRT1 inhibition caused cell death, while SIRT2 inhibition resulted in cell cycle arrest. In conclusion, we report the overexpression of SIRT2 and SIRT7 proteins in cervical cancer and suggest probable application of sirtuin inhibitors as therapeutic targets. Further, a specific increase in the levels of SIRT1 in intraepithelial lesion makes it a promising candidate for identification of preneoplastic changes.