CELL AGING--GROWTH FACTOR CONTROL OF EARLY RESPONSE GENE

随着正常人体细胞接近其增殖寿命的结束 它们无法通过复制它们的生长因子来对各种生长因子做出反应。 DNA. 我们广泛研究了WI-38细胞中的生长因子反应 并发现它们并不是由于必要的增长损失而产生的 因子受体或配体-受体相互作用的可识别变化。 事实上，许多正常的有丝分裂原刺激细胞周期依赖性事件， 衰老细胞中的活性和年轻细胞中的一样 进入S期的细胞。 这导致 推测衰老细胞在G1晚期被阻断， S阶段的开始。 最近我们和其他人（Campisi和同事个人通信） 已经观察到原癌基因c-fos的mRNA似乎是 在有丝分裂原刺激的衰老细胞中检测不到。 C的表达- fos是在有丝分裂原刺激后的非常早期的事件， 在年轻细胞中约0.5小时后的水平。 我们随后 观察到c-fos实际上在衰老的WI-38细胞中表达 表皮生长因子（EGF）的作用，但 只有当蛋白质合成同时被抑制时才能检测到， 放线菌酮。 这与不成比例的快速增长是一致的。 这种mRNA在衰老细胞中的降解。 我们打算研究 c-fos表达的调节和另外两个早期反应基因的调节， 年轻和衰老WI-38中c-jun和血清反应因子（SRF）的变化 细胞 我们将研究转录，蛋白质合成和 通过磷酸化的翻译后修饰。 我们还将直接 检测c-fos或c-jun是否能延长细胞增殖寿命， WI-38细胞，用含有这些质粒的质粒转化年轻细胞。 金属硫蛋白启动子控制下的正常基因。

As normal human cells approach the end of their proliferative lifespan they fail to respond to a variety of growth factors by replicating their DNA. We have examined growth factor responses extensively in WI-38 cells and have found that they do not result from the loss of necessary growth factor receptors or recognizable changes in ligand-receptor interactions. In fact, many of the normal mitogen stimulated cell cycle dependent events and activities are induced in senescent cells just as they are in young cells which do respond by entering the S phase. This has led to the speculation that senescent cells become blocked in late G1 near the beginning of the S phase. Recently we and others (Campisi and co-workers personal communication) have observed that the mRNA for the protooncogene c-fos appears to be undetectable in mitogen stimulated senescent cells. The expression of c- fos is a very early event following mitogen stimulation, reaching maximum levels after approximately 0.5 hr in young cells. We have subsequently observed that c-fos is actually expressed in senescent WI-38 cells following either serum or epidermal growth factor stimulation (EGF) but it is only detectable if protein synthesis is simultaneously inhibited with cycloheximide. This is consistent with the disproportionately rapid degradation of this mRNA in senescent cells. We intend to study the regulation of c-fos expression and that of two other early response genes, c-jun and the serum response factor (SRF) in young and senescent WI-38 cells. We will examine transcription, protein synthesis and posttranslational modification by phosphorylation. We will also directly test whether c-fos of c-jun can increase the proliferative life span of WI-38 cells by transforming young cells with plasmids containing these normal genes under the control of the metallothionein promotor.