Roles of Kruppel-associated Box (KRAB)-associated Co-repressor KAP1 Ser-473 Phosphorylation in DNA Damage Response

Chen Hu,Shengping Zhang,Xuan Gao,Xiaojing Gao,Xiaohong Xu,Ya Lv,Yan Zhang,Zhenhong Zhu,Changqing Zhang,Qiao Li,Jiemin Wong,Yongping Cui,Wen Zhang,Lin Ma,Chuangui Wang

doi:10.1074/jbc.m111.313262

Abstract

The Kruppel-associated box (KRAB)-associated co-repressor KAP1 is an essential nuclear co-repressor for the KRAB zinc finger protein superfamily of transcriptional factors. Ataxia telangiectasia mutated (ATM)-Chk2 and ATM- and Rad3-related (ATR)-Chk1 are two primary kinase signaling cascades activated in response to DNA damage. A growing body of evidence suggests that ATM and ATR phosphorylate KAP1 at Ser-824 in response to DNA damage and regulate KAP1-dependent chromatin condensation, DNA repair, and gene expression. Here, we show that, depending on the type of DNA damage that occurs, KAP1 Ser-473 can be phosphorylated by ATM-Chk2 or ATR-Chk1 kinases. Phosphorylation of KAP1 at Ser-473 attenuated its binding to the heterochromatin protein 1 family proteins and inhibited its transcriptional repression of KRAB-zinc finger protein (KRAB-ZFP) target genes. Moreover, KAP1 Ser-473 phosphorylation induced by DNA damage stimulated KAP1-E2F1 binding. Overexpression of heterochromatin protein 1 significantly inhibited E2F1-KAP1 binding. Elimination of KAP1 Ser-473 phosphorylation increased E2F1-targeted proapoptotic gene expression and E2F1-induced apoptosis in response to DNA damage. Furthermore, loss of phosphorylation of KAP1 Ser-473 led to less BRCA1 focus formation and slower kinetics of loss of γH2AX foci after DNA damage. KAP1 Ser-473 phosphorylation was required for efficient DNA repair and cell survival in response to DNA damage. Our studies reveal novel functions of KAP1 Ser-473 phosphorylation under stress.

Highlights

KAP1 is important for epigenetic modifications and the DNA damage response
As KAP1-heterochromatin protein 1 (HP1) interaction is crucial for chromatin dynamics, maintenance, and gene regulation [8], we examined whether DNA damage-induced KAP1 Ser-473 phosphorylation (S473p) can regulate its binding to HP1 family proteins (HP1 ␣, ␤, and ␥)
We showed that, depending on the type of DNA damage that occurs, KAP1 Ser-473 is phosphorylated by different DNA damage signaling pathways

Summary

Background

KAP1 is important for epigenetic modifications and the DNA damage response. Results: Distinct DNA damage signaling pathways regulate KAP1 Ser-473 phosphorylation (S473p). Elimination of KAP1 Ser473 phosphorylation increased E2F1-targeted proapoptotic gene expression and E2F1-induced apoptosis in response to DNA damage. KAP1 Ser-473 phosphorylation was required for efficient DNA repair and cell survival in response to DNA damage. KAP1 Ser-824 phosphorylation (S824p) and sumoylation affect the transcription of a subset of genes involved in cell cycle control and apoptosis in response to genotoxic stresses [19]. Chk is activated in an ATM-dependent or -independent manner [24], and it phosphorylates proteins such as p53 [25], Cdc25c [26], Strap [27], and E2F1 [28] and plays crucial roles in mediating the cellular checkpoint response, DNA repair, and apoptosis. KAP1 S473p is required for efficient DNA repair and cell survival in response to DNA damage under stress conditions

EXPERIMENTAL PROCEDURES

RESULTS

DISCUSSION