title: Dual modes of interaction between XRCC4 and polynucleotide kinase/phosphatase: implications for nonhomologous end joining.
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.
authors.affiliation: Department of Oncology, University of Alberta, Alberta, and the Cross Cancer Institute, Edmonton, Alberta T6G 1Z2, Canada.
authors.forename: Rajam S
authors.initials: RS
authors.lastname: Mani
authors.forename: Yaping
authors.initials: Y
authors.lastname: Yu
authors.forename: Shujuan
authors.initials: S
authors.lastname: Fang
authors.forename: Meiling
authors.initials: M
authors.lastname: Lu
authors.forename: Mesfin
authors.initials: M
authors.lastname: Fanta
authors.forename: Angela E
authors.initials: AE
authors.lastname: Zolner
authors.forename: Nasser
authors.initials: N
authors.lastname: Tahbaz
authors.forename: Dale A
authors.initials: DA
authors.lastname: Ramsden
authors.forename: David W
authors.initials: DW
authors.lastname: Litchfield
authors.forename: Susan P
authors.initials: SP
authors.lastname: Lees-Miller
authors.forename: Michael
authors.initials: M
authors.lastname: Weinfeld
mesh_terms: 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
chemical_list: 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