title: Phosphorylation of Rad9 at serine 328 by cyclin A-Cdk2 triggers apoptosis via interfering Bcl-xL.
abstract: 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.
authors.affiliation: Key Laboratory for Molecular Enzymology and Engineering of the Ministry of Education, College of Life Science, Jilin University, Changchun, China.
authors.forename: Zhuo
authors.initials: Z
authors.lastname: Zhan
authors.forename: Kan
authors.initials: K
authors.lastname: He
authors.forename: Dan
authors.initials: D
authors.lastname: Zhu
authors.forename: Dan
authors.initials: D
authors.lastname: Jiang
authors.forename: Ying-Hui
authors.initials: YH
authors.lastname: Huang
authors.forename: Yang
authors.initials: Y
authors.lastname: Li
authors.forename: Chao
authors.initials: C
authors.lastname: Sun
authors.forename: Ying-Hua
authors.initials: YH
authors.lastname: Jin
mesh_terms: D021581:Active Transport, Cell Nucleus / Q000187:drug effects; D017209:Apoptosis / Q000187:drug effects; D055162:Biocatalysis; D018797:Cell Cycle Proteins / Q000737:chemistry* / Q000378:metabolism*; D002467:Cell Nucleus / Q000187:drug effects / Q000378:metabolism; D019925:Cyclin A / Q000378:metabolism*; D051357:Cyclin-Dependent Kinase 2 / Q000378:metabolism*; D005047:Etoposide / Q000494:pharmacology; D006367:HeLa Cells; D006801:Humans; D008928:Mitochondria / Q000187:drug effects / Q000378:metabolism; D010766:Phosphorylation / Q000187:drug effects; D034622:RNA Interference; D012694:Serine / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects; D059005:Topoisomerase II Inhibitors / Q000494:pharmacology; D015854:Up-Regulation / Q000187:drug effects; D051020:bcl-X Protein / Q000172:deficiency* / Q000235:genetics
chemical_list: D018797:Cell Cycle Proteins; D019925:Cyclin A; D059005:Topoisomerase II Inhibitors; D051020:bcl-X Protein; C069930:rad9 protein; D012694:Serine; D005047:Etoposide; D051357:Cyclin-Dependent Kinase 2