Dual modes of interaction between XRCC4 and polynucleotide kinase/phosphatase: implications for nonhomologous end joining.
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.
Mani
Rajam S
RS
Department of Oncology, University of Alberta, Alberta, and the Cross Cancer Institute, Edmonton, Alberta T6G 1Z2, Canada.
Yu
Yaping
Y
Fang
Shujuan
S
Lu
Meiling
M
Fanta
Mesfin
M
Zolner
Angela E
AE
Tahbaz
Nasser
N
Ramsden
Dale A
DA
Litchfield
David W
DW
Lees-Miller
Susan P
SP
Weinfeld
Michael
M
D047390:Casein Kinase II / Q000235:genetics / Q000378:metabolism; D004247:DNA / Q000235:genetics / Q000378:metabolism; D011088:DNA Ligases / Q000235:genetics / Q000378:metabolism; D004260:DNA Repair; D045643:DNA Repair Enzymes / Q000235:genetics / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D006367:HeLa Cells; D006801:Humans; D010766:Phosphorylation; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000235:genetics / Q000378:metabolism*; D011485:Protein Binding; D017434:Protein Structure, Tertiary
D004268:DNA-Binding Proteins; C101467:XRCC4 protein, human; D004247:DNA; C530380:PNKP protein, human; D017853:Phosphotransferases (Alcohol Group Acceptor); D047390:Casein Kinase II; D011088:DNA Ligases; D045643:DNA Repair Enzymes