Sarabpreet Kaur

Publications (2)9.99 Total impact

• Article: Chk1-dependent constitutive phosphorylation of BLM helicase at serine 646 decreases after DNA damage.

  Sarabpreet Kaur, Priyanka Modi, Vivek Srivastava, Richa Mudgal, Shweta Tikoo, Prateek Arora, Debasisa Mohanty, Sagar Sengupta
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  ABSTRACT: BLM helicase, the protein mutated in Bloom syndrome, is involved in signal transduction cascades after DNA damage. BLM is phosphorylated on multiple residues by different kinases either after stress induction or during mitosis. Here, we have provided evidence that both Chk1 and Chk2 phosphorylated the NH(2)-terminal 660 amino acids of BLM. An internal region within the DExH motif of BLM negatively regulated the Chk1/Chk2-dependent NH(2)-terminal phosphorylation event. Using in silico analysis involving the Chk1 structure and its known substrate specificity, we predicted that Chk1 should preferentially phosphorylate BLM on serine 646 (Ser(646)). The prediction was validated in vitro by phosphopeptide analysis on BLM mutants and in vivo by usage of a newly generated phosphospecific polyclonal antibody. We showed that the phosphorylation at Ser(646) on BLM was constitutive and decreased rapidly after exposure to DNA damage. This resulted in the diminished interaction of BLM with nucleolin and PML isoforms, and consequently decreased BLM accumulation in the nucleolus and PML nuclear bodies. Instead, BLM relocalized to the sites of DNA damage and bound with the damage sensor protein, Nbs1. Mutant analysis confirmed that the binding to nucleolin and PML isoforms required Ser(646) phosphorylation. These results indicated that Chk1-mediated phosphorylation on BLM at Ser(646) might be a determinant for regulating subnuclear localization and could act as a marker for the activation status of BLM in response to DNA damage.
  Molecular Cancer Research 09/2010; 8(9):1234-47. · 4.29 Impact Factor
• Article: Phosphorylation-dependent interactions of BLM and 53BP1 are required for their anti-recombinogenic roles during homologous recombination.

  Vivek Tripathi, Sarabpreet Kaur, Sagar Sengupta
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  ABSTRACT: Mutations in bloom helicase protein (BLM) helicase cause Bloom syndrome, characterized by predisposition to almost all forms of cancer. We have demonstrated previously that endogenous BLM, signal transducer 53BP1 and RAD51 are present in a complex during replication stress. Using full-length recombinant proteins, we now provide evidence that these proteins physically interact. BLM interacts with checkpoint kinase (Chk) 1 via the kinetochore-binding domain (KBD). Wild-type (WT) Chk1 phosphorylates 53BP1 in the KBD, both in vitro and in vivo during replication stress. Chk1-mediated phosphorylation of 53BP1 enhances its binding to BLM and is required for the accumulation of 53BP1 at the site of stalled replication. 53BP1, in turn, binds to the N-terminal domain of BLM. Ataxia telangiectasia and Rad3 related (ATR)-mediated phosphorylation of BLM at Thr99 is critical for its interaction and subsequent co-localization with 53BP1. WT BLM enhances the interaction and co-localization between 53BP1 and RAD51 during replication arrest. Interactions between the three proteins have functional consequences. Non-binding or phosphorylation-deficient mutants of BLM and 53BP1 fail to demonstrate the anti-recombinogenic property of the WT counterparts. Consequently, these mutants cause elevation of endogenous RAD51 foci formation. These results provide evidence that the phosphorylation-mediated interactions between BLM, 53BP1 and RAD51 are required for their regulatory roles during homologous recombination.
  Carcinogenesis 02/2008; 29(1):52-61. · 5.70 Impact Factor