PDF(Pubmed)
Abstract：
The Ser/Thr protein phosphatase 2 A (PP2A) regulates the dephosphorylation of many phosphoproteins. Substrate recognition are mediated by B regulatory subunits. Here, we report the identification of a substrate conserved motif [RK]-V-x-x-[VI]-R in FAM122A, an inhibitor of B55α/PP2A. This motif is necessary for FAM122A binding to B55α, and computational structure prediction suggests the motif, which is helical, blocks substrate docking to the same site. In this model, FAM122A also spatially constrains substrate access by occluding the catalytic subunit. Consistently, FAM122A functions as a competitive inhibitor as it prevents substrate binding and dephosphorylation of CDK substrates by B55α/PP2A in cell lysates. FAM122A deficiency in human cell lines reduces the proliferation rate, cell cycle progression, and hinders G1/S and intra-S phase cell cycle checkpoints. FAM122A-KO in HEK293 cells attenuates CHK1 and CHK2 activation in response to replication stress. Overall, these data strongly suggest that FAM122A is a short helical motif (SHeM)-dependent, substrate-competitive inhibitor of B55α/PP2A that suppresses multiple functions of B55α in the DNA damage response and in timely progression through the cell cycle interphase.
摘要：
Ser/Thr蛋白磷酸酶2A（PP2A）调节许多磷蛋白的去磷酸化。底物识别由B调节亚基介导。这里,我们报告了FAM122A中底物保守基序[RK]-V-x-x-[VI]-R的鉴定，B55α/PP2A的抑制剂。该基序对于FAM122A与B55α结合是必需的，计算结构预测提出了这样的主题，这是螺旋的，块基板对接到同一地点。在这个模型中,FAM122A还通过阻塞催化亚基在空间上限制了底物的进入。始终如一，FAM122A作为竞争性抑制剂起作用,因为它防止细胞裂解物中的B55α/PP2A对CDK底物的底物结合和去磷酸化。人细胞系中的FAM122A缺乏会降低增殖率，细胞周期进程，并阻碍G1/S和S期细胞周期检查点。HEK293细胞中的FAM122A-KO减弱响应于复制应激的CHK1和CHK2活化。总的来说,这些数据强烈表明FAM122A是一个短螺旋基序（SHeM）依赖性，B55α/PP2A的底物竞争性抑制剂，可抑制B55α在DNA损伤反应中的多种功能，并及时通过细胞周期间期。
