Protein Phosphatase 6 Interacts with the DNA-Dependent Protein Kinase Catalytic Subunit and Dephosphorylates -H2AX

• Published in: Molecular and cellular biology 2010-03, Vol.30 (6), p.1368-1381
• Main Authors: Douglas, Pauline, Zhong, Jianing, Ye, Ruiqiong, G Moorhead, Greg B, Xu, Xingzhi, Lees-Miller, Susan P
• Format: Article
• Language: English
• ISSN: 0270-7306; 1098-5549
• DOI: 10.1128/MCB.00741-09

The catalytic subunit of the DNA-dependent protein kinase (DNA-PKcs) plays a major role in the repair of DNA double-strand breaks (DSBs) by nonhomologous end joining (NHEJ). We have previously shown that DNA-PKcs is autophosphorylated in response to ionizing radiation (IR) and that dephosphorylation by a protein phosphatase 2A (PP2A)-like protein phosphatase (PP2A, PP4, or PP6) regulates the protein kinase activity of DNA-PKcs. Here we report that DNA-PKcs interacts with the catalytic subunits of PP6 (PP6c) and PP2A (PP2Ac), as well as with the PP6 regulatory subunits PP6R1, PP6R2, and PP6R3. Consistent with a role in the DNA damage response, silencing of PP6c by small interfering RNA (siRNA) induced sensitivity to IR and delayed release from the G2/M checkpoint. Furthermore, siRNA silencing of either PP6c or PP6R1 led to sustained phosphorylation of histone H2AX on serine 139 (-H2AX) after IR. In contrast, silencing of PP6c did not affect the autophosphorylation of DNA-PKcs on serine 2056 or that of the ataxia-telangiectasia mutated (ATM) protein on serine 1981. We propose that a novel function of DNA-PKcs is to recruit PP6 to sites of DNA damage and that PP6 contributes to the dephosphorylation of -H2AX, the dissolution of IR-induced foci, and release from the G2/M checkpoint in vivo.