Key Laboratory for Molecular Enzymology and Engineering of the Ministry of Education, College of Life Science, Jilin University, Changchun, China.
PLoS One. 2012;7(9):e44923. doi: 10.1371/journal.pone.0044923. Epub 2012 Sep 13.
Cyclin A-Cdk2, a cell cycle regulated Ser/Thr kinase, plays important roles in a variety of apoptoticprocesses. However, the mechanism of cyclin A-Cdk2 regulated apoptosis remains unclear. Here, we demonstrated that Rad9, a member of the BH3-only subfamily of Bcl-2 proteins, could be phosphorylated by cyclin A-Cdk2 in vitro and in vivo. Cyclin A-Cdk2 catalyzed the phosphorylation of Rad9 at serine 328 in HeLa cells during apoptosis induced by etoposide, an inhibitor of topoisomeraseII. The phosphorylation of Rad9 resulted in its translocation from the nucleus to the mitochondria and its interaction with Bcl-xL. The forced activation of cyclin A-Cdk2 in these cells by the overexpression of cyclin A,triggered Rad9 phosphorylation at serine 328 and thereby promoted the interaction of Rad9 with Bcl-xL and the subsequent initiation of the apoptotic program. The pro-apoptotic effects regulated by the cyclin A-Cdk2 complex were significantly lower in cells transfected with Rad9S328A, an expression vector that encodes a Rad9 mutant that is resistant to cyclin A-Cdk2 phosphorylation. These findings suggest that cyclin A-Cdk2 regulates apoptosis through a mechanism that involves Rad9phosphorylation.
周期蛋白 A-Cdk2 是一种细胞周期调控的丝氨酸/苏氨酸激酶，在多种凋亡过程中发挥重要作用。然而，周期蛋白 A-Cdk2 调控凋亡的机制尚不清楚。在这里，我们证明了 Rad9，一种 Bcl-2 蛋白 BH3-only 亚家族的成员，可以被周期蛋白 A-Cdk2 在体外和体内磷酸化。在依托泊苷（拓扑异构酶 II 的抑制剂）诱导的细胞凋亡过程中，周期蛋白 A-Cdk2 在 HeLa 细胞中催化 Rad9 在丝氨酸 328 处的磷酸化。Rad9 的磷酸化导致其从核转移到线粒体，并与 Bcl-xL 相互作用。通过过度表达 cyclin A 在这些细胞中强制激活 cyclin A-Cdk2，触发 Rad9 在丝氨酸 328 处的磷酸化，从而促进 Rad9 与 Bcl-xL 的相互作用以及随后凋亡程序的启动。转染 Rad9S328A（一种表达载体，编码对周期蛋白 A-Cdk2 磷酸化有抗性的 Rad9 突变体）的细胞中，由周期蛋白 A-Cdk2 复合物调节的促凋亡作用明显降低。这些发现表明，周期蛋白 A-Cdk2 通过涉及 Rad9 磷酸化的机制来调节细胞凋亡。
