Research

Sagar Sengupta

M. Sc.
Calcutta University, India

Ph. D.
Indian Institute of Science, Bangalore, India

Postdoctoral Research
Institut de Genetique et de Biologie Moleculaire et Cellulaire, Strasbourg, France.
Laboratory of Human Carcinogenesis, National Cancer Institute, National
Institutes of Health, Bethesda, Maryland, USA.

Email
sagar@nii.res.in

 

Research Interest

DNA damage response, Signaling pathways altered in cancer, Post-translational modifications of proteins, Role of mitochondria in cancer, Bioimaging

Group Members

Suhas Kharat, Jyoti Kumari, Raina Priyadarshini, Vinoth Madhavan, Mansoor Hussain, Harish Batra, Radhey Shyam

Summary of Research

Work in the lab falls under two broad categories: Overview:

The broad aim of the research program has been to study the signaling pathways, which have undergone alterations during the process of cancer development. Tumor suppressors are a group of extremely specialized proteins whose mutations lead to the development of cancer. In other words they are the caretakers and gatekeepers of our body. We are focused on a unique group of proteins called RecQ helicase family, which are also called caretaker tumor suppressors. We chose this family of helicases as three of its members, BLM, WRN and RECQL4, when mutated lead to cancer predisposition syndromes called Bloom syndrome (BS), Werner Syndrome (WS) and Rothmund-Thomson syndrome (RTS) respectively. Work in the laboratory is presently focused on BLM and RECQL4 helicases.

A. BLM helicase and Bloom Syndrome
Bloom Syndrome (BS) is an autosomal recessive disorder. BS is characterized by proportional dwarfism, sun-induced chronic erythema, type II diabetes, male infertility and female subfertility and frequent infections due to immune deficiency. The most important characteristic of BS was the fact that these individuals are predisposed to cancer. Infact BS patients suffer from almost all the major types of cancer known to human. This indicates that BLM is possibly involved at an early (possibly regulatory) stage in many different types of cancer development. Though BS patients are rare, BLM heterozygotes (i.e. having one intact copy of BLM) are faced with a higher probability of developing colorectal cancer. The exact percentage of heterozygous individuals in general population is unknown. However in certain inbred populations the frequency of BLM heterozygotes is approximately 1 in 48,000. These factors indicate the usefulness of BLM as a protein and BS, as a cancer predisposition syndrome, in the study of cancer genetics. Under this project we are trying to understand:

1: Investigating the role of BLM during resolution of DNA damage by elucidating the role of BLM and RAD54 during HR

2: Investigating the role of BLM during sensing of DNA damage by understanding the role of constitutive BLM phosphorylation by Chk1 at Ser646

B. RECQL4 helicase and Rothmund Thomson Syndrome
Rothmund-Thomson Syndrome (RTS) is rare autosomal recessive disorder characterized by skin atrophy, telangiectasia, hyper- and hypopigmentation, congenital skeletal abnormalities, short stature, premature aging, and increased risk of malignant diseases including cancer predisposition, especially to osteosarcoma and lymphoma. Only 40 to 66% of patients with RTS have been found to have mutation in the RECQL4 gene, indicating genetic heterogeneity. The RECQL4 gene encodes a protein of 1208 amino acids with a centrally conserved helicase domain. The N-terminal region of RECQL4 has been implicated in the initiation of nuclear DNA replication. RECQL4 functions in prereplication complex formation and is required for chromatin binding  during initiation of DNA replication. Twoaof DNA polymerase  distinct domains of RECQL4, the conserved helicase motifs and the N-terminal Sld2 like domain, could independently exhibit helicase activity. Using overexpression based assays RECQL4 was characterized as a nuclear protein, containing an N-terminal nuclear localization signal (NLS). However, using antibodies against endogenous RECQL4, the protein was shown to have a cytoplasmic localization. This observation led us to determine the function of the cytoplasmic RECQL4. We specifically determined that the cytoplasmic RECQL4 is actually localized to the mitochondria. This project aims to investigate the role of RECQL4 in mitochondria.

Awards / Fellowships

National Bioscience award for Career Development, Department of Biotechnology, Government of India (2011)
Member, Guha Research Conference (2011)

Selected Publications

  • Kumar A, Tikoo S, Maity S, Sengupta S, Sengupta S, Kaur A, Bachhawat AK (2012) Mammalian proapoptotic factor ChaC1 and its homologues function as ?-glutamyl cyclotransferases acting specifically on glutathione. EMBO Rep. (In Press).
  • De S, Kumari J, Mudgal R, Modi P, Gupta S, Futami K, Goto H, Lindor NM, Furuichi Y, Mohanty D, Sengupta S** (2012) RECQL4 is essential for the transport of p53 to mitochondria in normal human cells in the absence of exogenous stress. J Cell Sci. 125: 2509-2522.
  • Tikoo S, Sengupta S** (2010). Time to Bloom. Genome Integr. 1:14.
  • Kaur S*, Modi P*, Srivastava V*, Mudgal R*, Tikoo S, Arora P, Mohanty D, Sengupta S** (2010) Chk1-dependent constitutive phosphorylation of BLM helicase at Serine 646 decreases after DNA damage. Mol Cancer Res. 8:1234-1247 (* signifies equal first authors).
  • Larrieu D, Ythier D, Binet R, Brambilla C, Brambilla E, Sengupta S, Pedeux R (2009) ING2 controls DNA replication forks progression to maintain genome stability. EMBO Rep. 10:1168-1174.
  • Mehta S, Miklos I, Sipiczki M, Sengupta S, Sharma N (2009) The Med8 mediator subunit interacts with the Rpb4 subunit of RNA polymerase II and Ace2 transcriptional activator in Schizosaccharomyces pombe. FEBS Lett. 583: 3115-3120.
  • Srivastava S*, Modi P*, Tripathi V, Mudgal R, De S, Sengupta S** (2009) BLM helicase stimulates the ATPase and chromatin remodeling activities of RAD54. J Cell Sci 122: 3093-3103 (* signifies equal first authors).
  • Tripathi V, Kaur S, Sengupta S** (2008) Phosphorylation-dependent interactions of BLM and 53BP1 are required for their anti-recombinogenic roles during homologous recombination. Carcinogenesis 29:52-61. 9.
  • Tripathi V, Nagarjuna T, Sengupta S** (2007) BLM helicase-dependent and independent roles of 53BP1 during replication stress mediated homologous recombination. J. Cell Biol. 178: 9-14.

** denotes publications as corresponding author

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