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

正常的哺乳动物细胞在培养中具有有限的分裂能力。 在完成它们的体外寿命后，它们进入非分裂状态 这被称为细胞衰老。 这一现象最 在正常人二倍体成纤维细胞中广泛研究。 一些 已经观察到当细胞变得 衰老 然而，尚无法确定哪些变化 是不同于细胞衰老的原因。 细胞 融合研究清楚地表明，衰老表型是 显性和不朽的细胞是由隐性变化的结果， 正常细胞程序 在过去的几年里， 衰老细胞产生DNA合成抑制剂的时间。 一 这种DNA合成抑制剂（SDI-1）是从衰老细胞中克隆得到 cDNA文库，并且是第一个被发现的一组Cdk抑制剂。 发现了 随后，已经克隆了六种Cdk抑制剂，其中许多 其在哺乳动物细胞中过表达时可抑制DNA合成。 Sdi 1（p21）的mRNA水平在衰老细胞中过表达10-20倍， 与年轻的人类二倍体成纤维细胞相比。 我们发现 在反义p21诱导后，降低p21的水平 序列，结果在刺激密度抑制，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不足以使它们 进入S期。 因此，我们假设，衰老的无能 细胞合成DNA可能是由于多个Cdk的过度表达 抑制剂，该项目的目标是确定Cdk的作用 细胞衰老的抑制剂。

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.