Department of Life Sciences

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http://presiuniv.ndl.gov.in:4009/handle/123456789/2326

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Browsing Department of Life Sciences by Subject "Biology and Biochemistry"

Now showing 1 - 3 of 3
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    Apoptosis regulators as targets for induction of apoptosis of Imatinib resistant chronic myeloid leukemia cells
    Biswas, Nabendu
    Apoptosis is a regulated cell death characterized by cell shrinkage, nuclear condensation, DNA fragmentation, membrane blebbing. There are several apoptosis regulators eg: BCL2, Bcl-xL, BAX, Survivin, FLIP, XIAP, cIAP etc. Targeting these apoptosis regulators may be a viable strategy for the treatment of cancer because one of the hallmarks of cancer is the deregulation of apoptosis. In our first study we tried to induce cell death in Imatinib-resistant chronic myelogenous Leukemia cell line K562, by using TRAIL, a well-studied anti-cancer agent. Normally these cells are also resistant to TRAIL. We used Hydroxychavicol, a Piper betel leaf derived polyphenol, to make this Imatinib- resistant K562 cells sensitive to TRAIL. In imatinib resistant K562 cells, XIAP, FLIP have emerged as targets by hydroxychavicol to sensitize the cells to TRAIL mediated apoptosis. Reactive Oxygen Species, particularly H2O2 has been shown to be a key player for this TRAIL sensitization by Hydroxychavicol. We found that ROS decreased XIAP, FLIP in imatinib sensitive K562(S) and imatinib resistant K562(R) both. These XIAP and cFLIP downregulation abrogated their inhibitory effect on Caspase activation and removed its break from extrinsic apoptotic pathway activation by TRAIL and this leads to apoptosis of Imatinib-resistant K562 cells and imatinib sensitive K562 cells. In Imatinibresistant K562 cells, FLIP and XIAP were differentially regulated by JNK and ERK respectively. Akt phosphorylation was decreased by ROS-activated ERK. Dephosphorylation of Akt inhibited its binding to XIAP and that lead to the destabilization of XIAP. On the other hand, ROS-activated JNK increased the expression of an ubiquitin ligase ITCH which degraded FLIP by binding to it and ubiquitination. However, interestingly, when we checked these finding on K562(S) cells, some of the findings were different. In K562(S) cells, ROS degrades XIAP, FLIP by lysosomal degradation pathway. Moreover, JNK alone instead of JNK and ERK played important role in this XIAP and FLIP downregulation. Thus, our findings suggest anti-apoptotic proteins XIAP and FLIP as a viable therapeutic target for Imatinib-resistant CML. We have also identified a novel ROS mediated regulatory pathway of these two proteins which may be further explored for therapeutic targets.
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    Comparative Analysis of Eukaryotic Homo sapiens and Oryza sativa indica Class IV Sirtuins
    Dey, Sanghamitra
    Sirtuins are a class of proteins biologically acting as epigenetic modulators. They are generally found to be involved in regulating the essential cellular processes like metabolism, aging and genome stability. In our studies we have investigated the class IV sirtuins to explore the mechanistic and regulatory aspect of this protein family. To understand the role of class IV sirtuins better we took representatives from both human and plant. Human class IV sirtuins HsSIRT6 and HsSIRT7 are nuclear and nucleolar proteins, respectively whereas OsSRT1 is a nuclear protein. Using HsSIRT6 as a control/model, we investigated the biochemical and epigenetic activities of HsSIRT7 and OsSRT1. From our studies, we found that N and C terminal region of these proteins have important role in their enzymatic activities and substrate recognition. N-terminal region in HsSIRT7 is associated with protein-protein interactions and C-terminus is often associated with subcellular localization. In case of OsSRT1, the extended C-terminal region plays important role in substrate recognition and catalysis. Sirtuins in general have a unique substrate specificity. There were available reports of H3K9Ac deacetylation by OsSRT1 and H3K18Ac deacetylation by HsSIRT7. Our studies shed light on its dual enzyme capability with preference for mono ADP ribosylation (mono ADPr) over deacetylation. Just like its plant counterpart, a comparison of these dual activities suggests HsSIRT7's preference for the mono ADPr transfer over its deacetylation of H3K18Ac. Several new targets for both the deacetylation and ADP ribosylation were detected. Class IV sirtuins can specifically transfer the single ADP ribose group on its substrates in an enzymatic manner. So, this study is the first one to report the ADP ribosylation activity in HsSIRT7 and OsSRT1, which were previously reported as only deacetylases. This mono ADPr effect is not well known in plants, more so for deacetylases. The products of this reaction (NAM and ADP ribose) have immense negative effect on these enzymes suggesting a tighter regulation. Under various ranges of abiotic stress conditions in rice plants, we could link this ADPr activity to the DNA repair pathway by activating the enzyme PARP1. The histone specific deacetylation is also related with OsSRT1 upregulation under these stress situations. Metal toxicity in plants also influences these enzyme activities. Mono ADP ribosylation in cells is often linked to different metabolic disease conditions. This kind of modification of transcription factors, p53 and ELK4 by HsSIRT7 may play a key role in maintaining the tumor phenotype. Thus, HsSIRT7 becomes an important therapeutic hotspot for drug designing to counter several disease conditions. Screening of several chemical compounds with HsSIRT7 active site has been carried out in this study.
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    Studies on the Protection of Arsenic Induced Reproductive Disorders in Adult Male Wistar Rats by Formulated High Protein Diet
    Mukhopadhyay, Prabir Kumar
    Arsenic toxicity is a major worldwide health problem and has been associated with several reproductive system disorders. The study was designed to investigate the protective role of casein–pea-enriched protein diet /formulated high protein diet (FHPD) on arsenic-mediated testicular and spermatozoal anomalies in adult Wistar rats. The rats (120±10gm) were randomly divided into three groups: Gr I (control) received the normal diet; the Gr II (treated) was given arsenic orally for 30 consecutive days as arsenic trioxide (3mg/kg/rat/day) where as Gr III (supplemented) was given isocaloric FHPD along with arsenic of same dose. Same animal model was used for the fulfilment of all the objectives. The results revealed significant reduction in weight of testis along with other accessory reproductive organs. Structural and functional alterations of testes, cauda epididymis and caudal spermatozoa were observed. Reduction of steroidogenesis, gonadotrophins and spermatogenesis were also noted. Increased oxidative stress resulted redox imbalance in testes, cauda epididymis and spermatozoa causing successive DNA damages. Apoptosis was initiated in testes as expression of apoptotic markers like Bax, Bcl-2, caspase 9 and caspase 3 were seen to be altered. Spermatozoal apoptosis was also noted by Annexin V-Pi staining. Arsenic deposition was also noted in testicular tissues. All these anomalies were attenuated when FHPD supplementation was given to arsenic-gavaged rats. Casein–pea-enriched protein diet/ FHPD mitigated the adverse effects of arsenic and helped in sustaining the normal reproductive functions.