title: The essential role of p21 in radiation-induced cell cycle arrest of vascular smooth muscle cell.
abstract: The biologic mechanisms for the success and failure of intravascular radiation therapy after angioplasty have not been well studied. We investigated the molecular mechanism of radiation-induced cell cycle arrest in vascular smooth muscle cell (VSMC) and examined whether p21 knock-out is a cause of radiation failure. Using different dosages of gamma radiation, we evaluated the effect of radiation on VSMC apoptosis and cell cycle progression, and its action mechanism. Irradiation significantly retarded the growth of cultured VSMC, which was not due to induction of apoptosis but mainly due to cell cycle arrest. Radiation showed remarkable cell cycle arrest at G1 and G2 phase (G0/G1:S:G2/M phases = 61%:34%:5% with 0 Gy versus 61%:9%:30% with 16 Gy, 12 h after radiation). In immunoblot analysis and kinase assay, radiation increased the expression of p21 and decreased the expression and activity of CDK2 and 1. In contrast, radiation did not affect the expression and activity of CDK4 and 6, nor the expression of p27 and p16. When p21 was knocked out, cell cycle of VSMC was not arrested by radiation, leading to increased proliferation. These finding provide the evidence that radiation inhibits VSMC proliferation through cell cycle arrest by enhancing p21 expression and suppressing CDK1 and 2. This observation supports the key role of p21 in radiation-induced cell cycle arrest and the degree of p21 expression may be the possible mechanism of radiation failure and delayed restenosis.
authors.affiliation: Department of Internal Medicine, Seoul National University College of Medicine, 28 Yongon-dong, Chongno-gu, Seoul 110-744, South Korea. hyosoo@snu.ac.kr
authors.forename: Hyo-Soo
authors.initials: HS
authors.lastname: Kim
authors.forename: Hyun-Jai
authors.initials: HJ
authors.lastname: Cho
authors.forename: Hyun-Ju
authors.initials: HJ
authors.lastname: Cho
authors.forename: Sun-Jung
authors.initials: SJ
authors.lastname: Park
authors.forename: Kyung-Woo
authors.initials: KW
authors.lastname: Park
authors.forename: In-Ho
authors.initials: IH
authors.lastname: Chae
authors.forename: Byung-Hee
authors.initials: BH
authors.lastname: Oh
authors.forename: Young-Bae
authors.initials: YB
authors.lastname: Park
authors.forename: Myoung-Mook
authors.initials: MM
authors.lastname: Lee
mesh_terms: D000818:Animals; D001011:Aorta / Q000166:cytology; D002453:Cell Cycle / Q000235:genetics / Q000502:physiology / Q000528:radiation effects; D018797:Cell Cycle Proteins / Q000032:analysis / Q000235:genetics / Q000502:physiology*; D049109:Cell Proliferation; D002478:Cells, Cultured; D023903:Coronary Restenosis / Q000235:genetics / Q000378:metabolism; D050759:Cyclin-Dependent Kinase Inhibitor p21; D018844:Cyclin-Dependent Kinases / Q000378:metabolism; D003593:Cytoplasm / Q000737:chemistry; D005720:Gamma Rays; D008297:Male; D051379:Mice; D008807:Mice, Inbred BALB C; D018345:Mice, Knockout; D009131:Muscle, Smooth, Vascular / Q000166:cytology / Q000378:metabolism / Q000528:radiation effects*; D032389:Myocytes, Smooth Muscle / Q000378:metabolism / Q000528:radiation effects; D051381:Rats; D017207:Rats, Sprague-Dawley
chemical_list: C493957:Cdkn1a protein, mouse; C493958:Cdkn1a protein, rat; D018797:Cell Cycle Proteins; D050759:Cyclin-Dependent Kinase Inhibitor p21; D018844:Cyclin-Dependent Kinases