Rosales Kimberly Romero, Reid Michael A, Yang Ying, Tran Thai Q, Wang Wen-I, Lowman Xazmin, Pan Min, Kong Mei
Department of Cancer Biology, Beckman Research Institute of City of Hope Cancer Center, Duarte, California, United States of America.
PLoS One. 2015 Dec 30;10(12):e0145938. doi: 10.1371/journal.pone.0145938. eCollection 2015.
Despite advances in our understanding of protein kinase regulation in the DNA damage response, the mechanism that controls protein phosphatase activity in this pathway is unclear. Unlike kinases, the activity and specificity of serine/threonine phosphatases is governed largely by their associated proteins. Here we show that Tip41-like protein (TIPRL), an evolutionarily conserved binding protein for PP2A-family phosphatases, is a negative regulator of protein phosphatase 4 (PP4). Knockdown of TIPRL resulted in increased PP4 phosphatase activity and formation of the active PP4-C/PP4R2 complex known to dephosphorylate γ-H2AX. Thus, overexpression of TIPRL promotes phosphorylation of H2AX, and increases γ-H2AX positive foci in response to DNA damage, whereas knockdown of TIPRL inhibits γ-H2AX phosphorylation. In correlation with γ-H2AX levels, we found that TIPRL overexpression promotes cell death in response to genotoxic stress, and knockdown of TIPRL protects cells from genotoxic agents. Taken together, these data demonstrate that TIPRL inhibits PP4 activity to allow for H2AX phosphorylation and the subsequent DNA damage response.
尽管我们对DNA损伤反应中蛋白激酶调控的理解有所进展，但该途径中控制蛋白磷酸酶活性的机制仍不清楚。与激酶不同，丝氨酸/苏氨酸磷酸酶的活性和特异性很大程度上由其相关蛋白决定。在此我们表明，Tip41样蛋白（TIPRL）是一种在进化上保守的PP2A家族磷酸酶结合蛋白，是蛋白磷酸酶4（PP4）的负调控因子。敲低TIPRL会导致PP4磷酸酶活性增加，并形成已知可使γ-H2AX去磷酸化的活性PP4-C/PP4R2复合物。因此，TIPRL的过表达促进H2AX的磷酸化，并在DNA损伤时增加γ-H2AX阳性灶，而敲低TIPRL则抑制γ-H2AX磷酸化。与γ-H2AX水平相关，我们发现TIPRL过表达会促进细胞在遗传毒性应激下死亡，而敲低TIPRL则保护细胞免受遗传毒性剂的影响。综上所述，这些数据表明TIPRL抑制PP4活性以允许H2AX磷酸化及随后的DNA损伤反应。
