Functional interaction between BLM helicase and 53BP1 in a Chk1-mediated pathway during S-phase arrest.

Sagar Sengupta,Irene M Ward,Remy Pedeux,André Nussenzweig,Junjie Chen,Curtis C Harris,Steven P Linke,Arkady Celeste,Natasha I Sinogeeva,Ana I Robles,Ran Zhang,Thanos D Halazonetis

doi:10.1083/jcb.200405128

Abstract

Bloom's syndrome is a rare autosomal recessive genetic disorder characterized by chromosomal aberrations, genetic instability, and cancer predisposition, all of which may be the result of abnormal signal transduction during DNA damage recognition. Here, we show that BLM is an intermediate responder to stalled DNA replication forks. BLM colocalized and physically interacted with the DNA damage response proteins 53BP1 and H2AX. Although BLM facilitated physical interaction between p53 and 53BP1, 53BP1 was required for efficient accumulation of both BLM and p53 at the sites of stalled replication. The accumulation of BLM/53BP1 foci and the physical interaction between them was independent of γ-H2AX. The active Chk1 kinase was essential for both the accurate focal colocalization of 53BP1 with BLM and the consequent stabilization of BLM. Once the ATR/Chk1- and 53BP1-mediated signal from replicational stress is received, BLM functions in multiple downstream repair processes, thereby fulfilling its role as a caretaker tumor suppressor.

Highlights

53BP1, first identified as a p53-interacting protein in a twohybrid screen (Iwabuchi et al, 1994), is a BRCT motif– containing protein that responds rapidly to different types of DNA damage (Schultz et al, 2000)
Gene KO models, and siRNA or antisense (AS)-treated cells, we have shown that BLM facilitated the interaction between p53 and 53BP1 during replicational stress. 53BP1 regulated the accumulation of BLM at sites of DNA damage even in the absence of ␥-H2AX
The colocalization factors for the same pairs of foci were much less when the cells were subjected to the same synchronization protocol, but were not treated with HU, indicating that the colocalization were a result of HU-mediated replicational stress and not due to the synchronization protocol (Fig. S1 B)

Summary

Introduction

This response involves the ATM-dependent checkpoint pathway, thought to be constitutively active in certain human cancers (Rappold et al, 2001; DiTullio et al, 2002). Though the involvement of H2AX and 53BP1 in response to IR has been extensively investigated, much less is known about the role of sensor proteins during replicational stress.

Methods

Results

Conclusion