title: Protein kinase C inhibits the CAK-CDK2 cyclin-dependent kinase cascade and G1/S cell cycle progression in human diploid fibroblasts.
abstract: Serum stimulation of human diploid fibroblast IMR-90 cells leads to phosphorylation of p33CDK2 at Thr160 and activation of CDK2 kinase, a necessary event for G1/S transition. We report that serum stimulation causes a gradual, sustained increase in the activity of CDK-activating kinase (CAK) that phosphorylates CDK2 at Thr160, which starts by 5 h after serum stimulation and reaches the maximal plateau level at around the G1/S boundary. In this cell type addition of phorbol-12, 13-dibutyrate 5 h but not 16 h after serum stimulation completely inhibits CDK2 kinase activation and DNA synthesis. Phorbol ester treatment does not reduce the protein level of p33CDK2, but does inhibit serum-stimulated increases in the CAK activity and CDK2 phosphorylation at Thr160. The suppression of the CAK activity by the phorbol ester is accompanied by decreases in the message levels of both CDK7 and cyclin H, the catalytic and the positive regulatory subunit of CAK, respectively. These results indicate that in IMR-90 cells activation of protein kinase C in the late G1 phase causes cell cycle arrest before the G1/S boundary at least in part through downregulation of CAK and CAK-mediated CDK2 phosphorylation and activation.
authors.affiliation: Department of Cardiovascular Biology, Faculty of Medicine, University of Tokyo, Bunkyo-ku, Japan.
authors.forename: K
authors.initials: K
authors.lastname: Hamada
authors.forename: N
authors.initials: N
authors.lastname: Takuwa
authors.forename: W
authors.initials: W
authors.lastname: Zhou
authors.forename: M
authors.initials: M
authors.lastname: Kumada
authors.forename: Y
authors.initials: Y
authors.lastname: Takuwa
mesh_terms: D000906:Antibodies / Q000276:immunology; D042846:CDC2-CDC28 Kinases; D002453:Cell Cycle / Q000187:drug effects; D002460:Cell Line; D056748:Cyclin H; D051357:Cyclin-Dependent Kinase 2; D018844:Cyclin-Dependent Kinases / Q000037:antagonists & inhibitors* / Q000096:biosynthesis; D016213:Cyclins / Q000235:genetics; D000070819:Discoidin Domain Receptor 1; D006801:Humans; D015240:Phorbol 12,13-Dibutyrate / Q000494:pharmacology; D010766:Phosphorylation; D011493:Protein Kinase C / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases / Q000037:antagonists & inhibitors* / Q000096:biosynthesis / Q000235:genetics / Q000276:immunology; D012333:RNA, Messenger / Q000032:analysis; D020794:Receptor Protein-Tyrosine Kinases / Q000032:analysis / Q000378:metabolism; D000095043:Cyclin-Dependent Kinase-Activating Kinase
chemical_list: D000906:Antibodies; C534751:CCNH protein, human; D056748:Cyclin H; D016213:Cyclins; D012333:RNA, Messenger; D015240:Phorbol 12,13-Dibutyrate; C092030:DDR1 protein, human; D000070819:Discoidin Domain Receptor 1; D020794:Receptor Protein-Tyrosine Kinases; D017346:Protein Serine-Threonine Kinases; D011493:Protein Kinase C; D042846:CDC2-CDC28 Kinases; C495894:CDK2 protein, human; D051357:Cyclin-Dependent Kinase 2; D018844:Cyclin-Dependent Kinases; D000095043:Cyclin-Dependent Kinase-Activating Kinase; C000722416:CDK7 protein, human