title: Expression and activities of cyclins and cyclin-dependent kinases in developing rat ventricular myocytes.
abstract: The molecular mechanisms responsible for the alterations in proliferative capacity of cardiac myocytes during development remain unknown; however, cell cycle dependent molecules may be involved. We have determined the expression of cyclins A, D1-3 and E, and cyclin-dependent kinases (CDKs) 2, 4, 5 and 6 and cdc2 in freshly isolated rat cardiac myocytes from fetal (18 days gestation), neonatal (2 days post-natal) and adult animals by immunoblotting. Our results show a dramatic decrease in expression of these proteins during normal cardiac development, such that levels are highest in fetal myocytes but are significantly down-regulated in adult cells (P<0.05, in each case). We also have determined the in vitro kinase activities of cdc2, CDK2, CDK4, CDK5 and CDK6 immunocomplexes in fetal, neonatal and adult myocytes. There was a consistent and significant loss of cdc2, CDK2, CDK4 and CDK6 kinase activities in adult cardiac cell lysates (5.3-, 10.6-, 1.5- and 1.9-fold decreases, respectively) when compared to neonatal samples (P<0.05); CDK5 activity showed a similar trend but failed to reach significance. In conclusion, our results show that the expression and activities of various positive regulators of the cell cycle are down-regulated significantly during development of the cardiac myocyte, concomitant with the loss of proliferative capacity in adult myocytes. Down-regulation of these proteins may be pivotal in the withdrawal of the cardiac myocyte from the cell cycle.
authors.affiliation: Cardiovascular Cellular and Molecular Biology, Cardiovascular Research, The Rayne Institute, St Thomas' Hospital, London, SE1 7EH, UK.
authors.forename: G
authors.initials: G
authors.lastname: Brooks
authors.forename: R A
authors.initials: RA
authors.lastname: Poolman
authors.forename: C J
authors.initials: CJ
authors.lastname: McGill
authors.forename: J M
authors.initials: JM
authors.lastname: Li
mesh_terms: D016475:3T3 Cells; D000818:Animals; D000831:Animals, Newborn; D002453:Cell Cycle; D002478:Cells, Cultured; D018844:Cyclin-Dependent Kinases / Q000096:biosynthesis* / Q000235:genetics; D016213:Cyclins / Q000096:biosynthesis* / Q000235:genetics; D004790:Enzyme Induction; D005318:Fetal Heart / Q000166:cytology / Q000378:metabolism*; D018507:Gene Expression Regulation, Developmental; D005865:Gestational Age; D006352:Heart Ventricles / Q000254:growth & development / Q000378:metabolism; D051379:Mice; D009206:Myocardium / Q000166:cytology / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar
chemical_list: D016213:Cyclins; D018844:Cyclin-Dependent Kinases