ROLE OF CYCLIN DEPENDENT KINASE (CDK) INHIBITORS IN CELLULAR SENESCENCE

正常的哺乳动物细胞在培养中的分裂能力有限。 在完成体外寿命后，它们进入不分裂状态 这被称为细胞衰老。这种现象是最多的 在正常人二倍体成纤维细胞中进行了广泛的研究。一批 已经观察到当细胞变成 衰老了。然而，目前还无法确定哪些变化 其原因与细胞衰老的结果不同。细胞 Fusion研究清楚地表明，衰老的表型是 而不朽细胞是由细胞中的隐性变化产生的 正常的细胞程序。在过去的几年里积累了一些证据 衰老细胞产生脱氧核糖核酸合成的抑制物(S)的时间。一 这种DNA合成抑制物(SDI-1)是从衰老细胞中克隆出来的 CDNA库，是一组CDK抑制剂中第一个被 被发现了。随后，已经克隆了六种CDK抑制剂，其中许多 当在哺乳动物细胞中过度表达时，它可以抑制DNA合成。 在衰老过程中，Sdi1(P21)的mRNA水平高表达10-20倍 与年轻的人二倍体成纤维细胞相比。我们发现， 反义p21诱导后p21基因表达水平的降低 序列，导致密度抑制的刺激，年轻人 成纤维细胞进行DNA合成和分裂。然而，表达 衰老的人类细胞中的反义p21不足以导致它们 进入S阶段。因此，我们假设，衰老的能力 细胞合成DNA可能是由于多个CDK的过度表达 抑制剂，这个项目的目标是确定CDK的作用 细胞衰老中的抑制剂。

Normal mammalian cells have a finite capacity for division in culture. After completing their in vitro lifespan they enter a non-dividing state that has been termed cellular senescence. This phenomenon has been most extensively studied in normal human diploid fibroblasts. A number of changes in gene expression have been observed when cells become senescent. However, it has not been possible to determine which changes are the cause as distinct from the result of cellular senescence. Cell fusion studies have clearly demonstrated that the senescent phenotype is dominant and that immortal cells result from recessive changes in the normal cell program. Evidence has accumulated over the past several years that senescent cells produce an inhibitor(s) of DNA synthesis. One such DNA synthesis inhibitor (SDI-1) was cloned from a senescent cell cDNA library, and was the first of a group of Cdk inhibitors to be discovered. Subsequently, six Cdk inhibitors have been cloned, many of which can inhibit DNA synthesis when over-expressed in mammalian cells. The mRNA level of Sdi1 (p21) is over-expressed 10-20 fold in senescent compared with young human diploid fibroblasts. We have found that decreasing the level of p21, following induction of antisense p21 sequences, results in stimulation of density inhibited, young human fibroblasts to undergo DNA synthesis and divide. However, expression of antisense p21 in senescent human cells is not sufficient to cause them to enter S phase. Therefore, we hypothesize that the inability of senescent cells to synthesize DNA may be due to the over-expression of multiple Cdk inhibitors, and the goal of this project is to determine the role of Cdk inhibitors in cellular senescence.