DNA damage‐induced allosteric activation of protein phosphatase PP1:NIPP1 through Src kinase‐induced circularization of NIPP1

Abstract

Protein phosphatase‐1 (PP1) complexed to nuclear inhibitor of PP1 (NIPP1) limits DNA repair through dephosphorylation of NIPP1‐recruited substrates. However, the PP1:NIPP1 holoenzyme is completely inactive under basal conditions, hinting at a DNA damage‐regulated activation mechanism. Here, we report that DNA damage caused the activation of PP1:NIPP1 after a time delay of several hours through phosphorylation of NIPP1 at the C‐terminal tyrosine 335 (Y335) by a Src‐family kinase. PP1:NIPP1 activation partially resulted from the dissociation of the C terminus of NIPP1 from the active site of PP1. In addition, the released Y335‐phosphorylated C terminus interacted with the N terminus of NIPP1 to enhance substrate recruitment by the flanking forkhead‐associated (FHA) domain. Constitutive activation of PP1:NIPP1 by knock‐in of a phospho‐mimicking (Y335E) NIPP1 mutant led to the hypo‐phosphorylation of FHA ligands and an accumulation of DNA double‐strand breaks. Our data indicate that PP1:NIPP1 activation through circularization of NIPP1 is a late response to DNA damage that contributes to the timely recovery from damage repair.