Roles of nibrin and ATM/ATR kinases on the G2 checkpoint under endogenous or radio-induced DNA damage

Katherine Marcelain,Patricio González,Consuelo De La Torre,Juana Pincheira

doi:10.4067/s0716-97602005000200007

Katherine Marcelain, Patricio González + Show 2 more

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https://doi.org/10.4067/s0716-97602005000200007

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Abstract

Checkpoint response to DNA damage involves the activation of DNA repair and G2 lengthening subpathways. The roles of nibrin (NBS1) and the ATM/ATR kinases in the G2 DNA damage checkpoint, evoked by endogenous and radio-induced DNA damage, were analyzed in control, A-T and NBS lymphoblast cell lines. Short-term responses to G2 treatments were evaluated by recording changes in the yield of chromosomal aberrations in the ensuing mitosis, due to G2 checkpoint adaptation, and also in the duration of G2 itself. The role of ATM/ATR in the G2 checkpoint pathway repairing chromosomal aberrations was unveiled by caffeine inhibition of both kinases in G2. In the control cell lines, nibrin and ATM cooperated to provide optimum G2 repair for endogenous DNA damage. In the A-T cells, ATR kinase substituted successfully for ATM, even though no G2 lengthening occurred. X-ray irradiation (0.4 Gy) in G2 increased chromosomal aberrations and lengthened G2, in both mutant and control cells. However, the repair of radio-induced DNA damage took place only in the controls. It was associated with nibrin-ATM interaction, and ATR did not substitute for ATM. The absence of nibrin prevented the repair of both endogenous and radio-induced DNA damage in the NBS cells and partially affected the induction of G2 lengthening.

Highlights

Cell response to DNA damage in G2 involves the activation of a signal transduction pathway, known as the G2 checkpoint, that masters two parallel subpathways
To evaluate the participation of nibrin, ATM and ATR in the repair of endogenous DNA damage during G2, we studied the short-term response to 5 mM caffeine inhibition of both kinases (Sarkaria et al, 1999), during the last 3 hours before mitosis
The processing of DNA lesions during G2 involves the activation of the corresponding checkpoint, which in turn induces the repair of nuclear DNA damage and, the lengthening of G2

Summary

Introduction

Cell response to DNA damage in G2 involves the activation of a signal transduction pathway, known as the G2 checkpoint, that masters two parallel subpathways One of these activates the repair of DNA lesions, while the other delays the G2 to mitosis transition (Weinert, 1997; Ward & Chen, 2004). The latter subpathway is brought about by transient inactivation of the CDK-mitotic cyclin heterodimer, mediated by the ATMChk kinases pathway (Abraham, 2001). This allows the cell to have additional time in G2 to repair its damaged DNA before the transition to mitosis takes place (Rhind & Russell, 2000). The cell again may reinitiate cycle progression but only when the environmental or endogenous changes reinduce the transcriptional program interrupted earlier

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