Dual Modes of Interaction between XRCC4 and Polynucleotide Kinase/Phosphatase: Implications for Nonhomologous End Joining

Authors

Rajam S. Mani, University of Alberta
Yaping Yu, University of Calgary
Shujuan Fang, University of Calgary
Meiling Lu, University of Alberta
Mesfin Fanta, University of Alberta
Angela E. Zolner, University of Calgary
Nasser Tahbaz, University of Alberta
Dale A. Ramsden, University of North Carolina at Chapel Hill
David W. Litchfield, The University of Western OntarioFollow
Susan P. Lees-Miller, University of Calgary
Michael Weinfeld, University of Alberta

Document Type

Article

Publication Date

11-26-2010

Journal

The Journal of Biological Chemistry

Volume

285

Issue

48

First Page

37619

Last Page

37629

URL with Digital Object Identifier

http://dx.doi.org/10.1074/jbc.M109.058719

Abstract

XRCC4 plays a crucial role in the nonhomologous end joining (NHEJ) pathway of DNA double-strand break repair acting as a scaffold protein that recruits other NHEJ proteins to double-strand breaks. Phosphorylation of XRCC4 by protein kinase CK2 promotes a high affinity interaction with the forkhead-associated domain of the end-processing enzyme polynucleotide kinase/phosphatase (PNKP). Here we reveal that unphosphorylated XRCC4 also interacts with PNKP through a lower affinity interaction site within the catalytic domain and that this interaction stimulates the turnover of PNKP. Unexpectedly, CK2-phosphorylated XRCC4 inhibited PNKP activity. Moreover, the XRCC4·DNA ligase IV complex also stimulated PNKP enzyme turnover, and this effect was independent of the phosphorylation of XRCC4 at threonine 233. Our results reveal that CK2-mediated phosphorylation of XRCC4 can have different effects on PNKP activity, with implications for the roles of XRCC4 and PNKP in NHEJ.