Poolman R A, Brooks G
Cardiovascular Cellular and Molecular Biology, The Rayne Institute, St Thomas>> Hospital, London, SE1 7EH, UK.
J Mol Cell Cardiol. 1998 Oct;30(10):2121-35. doi: 10.1006/jmcc.1998.0808.
The role of cell cycle dependent molecules in controlling the switch from cardiac myocyte hyperplasia to hypertrophy remains unclear, although in the rat this process occurs between day 3 and 4 after birth. In this study we have determined (1) cell cycle profiles by fluorescence activated cell sorting (FACS); and (2) expressions, co-expressions and activities of a number of cyclins, cyclin-dependent kinases (CDKs) and CDK inhibitors by reverse transcriptase-polymerase chain reaction (RT-PCR), immunoblotting and in vitro kinase assays in freshly isolated rat cardiac myocytes obtained from 2, 3, 4 and 5-day-old animals. The percentage of myocytes found in the S phase of the cell cycle decreased significantly during the transition from hyperplasia to hypertrophy (5.5, 3.5, 2.3 and 1.9% of cells in 2-, 3-, 4- and 5-day-old myocytes, respectively,P<0.05), concomitant with a significant increase in the percentage of G0/G1 phase cells. At the molecular level, the expressions and activities of G1/S and G2/M phase acting cyclins and CDKs were downregulated significantly during the transition from hyperplasia to hypertrophy, whereas the expressions and activities of G1 phase acting cyclins and CDKs were upregulated significantly during this transition. In addition, p21(CIP1)- and p27(KIP1)- associated CDK kinase activities remained relatively constant when histone H1 was used as a substrate, whereas phosphorylation of the retinoblastoma protein was upregulated significantly during the transition from hyperplasia to hypertrophy. Thus, there is a progressive and significant G0/G1 phase blockade during the transition from myocyte hyperplasia to hypertrophy. Whilst CDK2 and cdc2 may be pivotal in the withdrawal of cardiac myocytes from the cell cycle, CDK4 and CDK6 may be critical for maintaining hypertrophic growth of the myocyte during development.
尽管在大鼠中，心肌细胞从增生向肥大的转变过程发生在出生后第3天到第4天之间，但细胞周期依赖性分子在控制这一转变过程中的作用仍不清楚。在本研究中，我们通过荧光激活细胞分选（FACS）确定了（1）细胞周期概况；并通过逆转录聚合酶链反应（RT-PCR）、免疫印迹和体外激酶分析，测定了从2、3、4和5日龄动物新鲜分离的大鼠心肌细胞中多种细胞周期蛋白、细胞周期蛋白依赖性激酶（CDK）和CDK抑制剂的表达、共表达及活性。在从增生向肥大的转变过程中，处于细胞周期S期的心肌细胞百分比显著下降（2、3、4和5日龄心肌细胞中分别为5.5%、3.5%、2.3%和1.9%的细胞，P<0.05），同时G0/G1期细胞百分比显著增加。在分子水平上，从增生向肥大转变过程中，作用于G1/S期和G2/M期的细胞周期蛋白和CDK的表达及活性显著下调，而作用于G1期的细胞周期蛋白和CDK的表达及活性在这一转变过程中显著上调。此外，当以组蛋白H1为底物时，与p21（CIP1）和p27（KIP1）相关的CDK激酶活性保持相对恒定，而在从增生向肥大的转变过程中，视网膜母细胞瘤蛋白的磷酸化显著上调。因此，在心肌细胞从增生向肥大的转变过程中，存在着逐渐且显著的G0/G1期阻滞。虽然CDK2和cdc2可能在心肌细胞退出细胞周期中起关键作用，但CDK4和CDK6可能对发育过程中心肌细胞维持肥大生长至关重要。
