https://dspace.nii.res.in//https://dspace.nii.res.in/handle/123456789/41 Principal Investigator- Dr. Sagar Sengupta Mon, 27 Apr 2026 15:40:42 GMT 2026-04-27T15:40:42Z https://dspace.nii.res.in:443/retrieve/50b10997-ec07-4d49-9d80-283cab46cb4e/Dr. Sagar Sengupta.JPG https://dspace.nii.res.in//https://dspace.nii.res.in/handle/123456789/41 https://dspace.nii.res.in//https://dspace.nii.res.in/handle/123456789/1578 Title: p53 regulates DREAM complex-mediated repression in a p21-independent manner Authors: Sengupta, Sagar; Agrawal, Ritu Abstract: The DREAM repressor complex regulates genes involved in the cell cycle and DNA repair, vital for maintaining genome stability. Although it mediates p53-driven repression through the canonical p53-p21-Rb axis, the potential for p53 to directly regulate DREAM targets independently of its transcriptional activity has not been explored. Here, we demonstrate that in asynchronously growing cells, p53 loss leads to greater de-repression of DREAM targets compared to p21 loss alone. Both wild-type and transactivation-deficient p53 mutants are capable of repressing DREAM targets, suggesting a transactivation-independent "non-canonical" repression mechanism. These p53 variants bind p130/p107, irrespective of their phosphorylation status, while cancer-associated p53 mutants disrupt DREAM complex function by sequestering E2F4. Re-ChIP analysis shows co-recruitment of p53 and E2F4 to known and newly identified DREAM target promoters, indicating direct repression of these targets by p53. These findings reveal a novel, transactivation-independent mechanism of p53-mediated repression, expanding our understanding of p53's tumor-suppressive functions and suggesting DREAM complex targeting as potential future avenues in cancer therapy. Wed, 01 Jan 2025 00:00:00 GMT https://dspace.nii.res.in//https://dspace.nii.res.in/handle/123456789/1578 2025-01-01T00:00:00Z https://dspace.nii.res.in//https://dspace.nii.res.in/handle/123456789/1575 Title: Phosphorylated BLM peptide acts as an agonist for DNA damage response Authors: Agrawal, Ritu; Agarwal, Himanshi; Mukherjee, Chetana; Chakraborty, Baishali; Sharma, Vandana; Tripathi, Vivek; Kumar, Nitin; Priya, Swati; Gupta, Nidhi; Jhingan, Gagan Deep; Bajaj, Avinash; Sengupta, Sagar Abstract: Upon exposure to ionizing irradiation, the MRE11-RAD50-NBS1 complex potentiates the recruitment of ATM (ataxia-telangiectasia mutated) kinase to the double-strand breaks. We show that the lack of BLM causes a decrease in the autophosphorylation of ATM in mice mammary glands, which have lost one or both copies of BLM. In isogenic human cells, the DNA damage response (DDR) pathway was dampened in the absence of BLM, which negatively affected the recruitment of DDR factors onto the chromatin, thereby indicating a direct role of BLM in augmenting DDR. Mechanistically, this was due to the BLM-dependent dissociation of inactive ATM dimers into active monomers. Fragmentation analysis of BLM followed by kinase assays revealed a 20-mer BLM peptide (91-110 aa), sufficient to enhance ATM-dependent p53 phosphorylation. ATM-mediated phosphorylation of BLM at Thr99 within BLM (91-110) peptide enhanced ATM kinase activity due to its interaction with NBS1 and causing ATM monomerization. Delivery of phosphomimetic T99E counterpart of BLM (91-110 aa) peptide led to ATM activation followed by restoration of the DDR even in the absence of ionizing irradiation (both in cells and in BLM knockout mice), indicating its role as a DDR agonist, which can be potentially used to prevent the initiation of neoplastic transformation. Wed, 01 Jan 2025 00:00:00 GMT https://dspace.nii.res.in//https://dspace.nii.res.in/handle/123456789/1575 2025-01-01T00:00:00Z https://dspace.nii.res.in//https://dspace.nii.res.in/handle/123456789/1573 Title: Regulation of pathway choice in DNA repair after double-strand breaks Authors: Kumari, Nitu; Kaur, Ekjot; Raghavan, Sathees C; Sengupta, Sagar Abstract: DNA damage signaling is a highly coordinated cellular process which is required for the removal of DNA lesions. Amongst the different types of DNA damage, double-strand breaks (DSBs) are the most harmful type of lesion that attenuates cellular proliferation. DSBs are repaired by two major pathways-homologous recombination (HR), and non-homologous end-joining (NHEJ) and in some cases by microhomology-mediated end-joining (MMEJ). Preference of the pathway depends on multiple parameters including site of the DNA damage, the cell cycle phase and topology of the DNA lesion. Deregulated repair response contributes to genomic instability resulting in a plethora of diseases including cancer. This review discusses the different molecular players of HR, NHEJ, and MMEJ pathways that control the switch among the different DSB repair pathways. We also highlight the various functions of chromatin modifications in modulating repair response and how deregulated DNA damage repair response may promote oncogenic transformation. Wed, 01 Jan 2025 00:00:00 GMT https://dspace.nii.res.in//https://dspace.nii.res.in/handle/123456789/1573 2025-01-01T00:00:00Z https://dspace.nii.res.in//https://dspace.nii.res.in/handle/123456789/1548 Title: Hyperubiquitylation of DNA helicase RECQL4 by E3 ligase MITOL prevents mitochondrial entry and potentiates mitophagy Authors: Hussain, Mansoor; Mohammed, Aftab; Saifi, Shabnam; Priya, Swati; Sengupta, Sagar Abstract: Mutations in the DNA helicase RECQL4 lead to Rothmund-Thomson syndrome (RTS), a disorder characterized by mitochondrial dysfunctions, premature aging, and genomic instability. However, the mechanisms by which these mutations lead to pathology are unclear. Here we report that RECQL4 is ubiquitylated by a mitochondrial E3 ligase, MITOL, at two lysine residues (K1101, K1154) via K6 linkage. This ubiquitylation hampers the interaction of RECQL4 with mitochondrial importer Tom20, thereby restricting its own entry into mitochondria. We show the RECQL4 2K mutant (where both K1101 and K1154 are mutated) has increased entry into mitochondria and demonstrates enhanced mitochondrial DNA (mtDNA) replication. We observed that the three tested RTS patient mutants were unable to enter the mitochondria and showed decreased mtDNA replication. Furthermore, we found that RECQL4 in RTS patient mutants are hyperubiquitylated by MITOL and form insoluble aggregate-like structures on the outer mitochondrial surface. However, depletion of MITOL allows RECQL4 expressed in these RTS mutants to enter mitochondria and rescue mtDNA replication. Finally, we show increased accumulation of hyperubiquitylated RECQL4 outside the mitochondria leads to the cells being potentiated to increased mitophagy. Hence, we conclude regulating the turnover of RECQL4 by MITOL may have a therapeutic effect in patients with RTS. Sun, 01 Jan 2023 00:00:00 GMT https://dspace.nii.res.in//https://dspace.nii.res.in/handle/123456789/1548 2023-01-01T00:00:00Z