Sgambato A, Han E K, Zhou P, Schieren I, Weinstein I B
Columbia-Presbyterian Cancer Center, Columbia University, New York 10032, USA.
Cancer Res. 1996 Mar 15;56(6):1389-99.
To elucidate the role of cyclin E in cell growth and tumorigenesis in mammary epithelial cells, we have used retrovirus-mediated transduction to generate derivatives of the nontransformed HC11 mouse mammary epithelial cell line that stably express a human cyclin E cDNA (HU4). These derivatives expressed two distinct forms of the exogenous cyclin E protein, which were about M(r) 50,000 and M(r) 42,000, thus corresponding to endogenous cyclin E proteins found in human cells. In contrast to results obtained previously in fibroblasts, overexpression of the HU4 cyclin E cDNA in HC11 cells was associated with an increase in cell size, lengthening of G(1), and inhibition of both anchorage-dependent and independent growth. Furthermore, when quiescent serum-starved cells were restimulated with serum, entry into the S-phase was delayed in the overexpressor cells. Under these conditions, there was also delayed induction in the expression of the endogenous cyclin E protein and in other events involved in the G(1) transition. Despite the high level of expression of the exogenous cyclin E, the derivatives did not display increased cyclin E-associated in vitro kinase activity. The HC11 cells that overexpressed the exogenous cyclin E displayed an increase in the cyclin/cyclin-dependent kinase inhibitor p27(Kip1) in both asynchronous exponentially dividing and synchronous cell populations. These findings indicate that increased expression of this cyclin E cDNA in HC11 cells inhibits rather than stimulates growth and that this may be due to increased expression of the inhibitor p27(Kip1).
为了阐明细胞周期蛋白E在乳腺上皮细胞的细胞生长和肿瘤发生中的作用，我们利用逆转录病毒介导的转导技术，生成了稳定表达人细胞周期蛋白E cDNA（HU4）的非转化HC11小鼠乳腺上皮细胞系的衍生物。这些衍生物表达了两种不同形式的外源性细胞周期蛋白E蛋白，其分子量分别约为50,000和42,000，因此与在人细胞中发现的内源性细胞周期蛋白E蛋白相对应。与先前在成纤维细胞中获得的结果相反，HC11细胞中HU4细胞周期蛋白E cDNA的过表达与细胞大小增加、G1期延长以及贴壁依赖性和非依赖性生长的抑制有关。此外，当用血清重新刺激静止的血清饥饿细胞时，过表达细胞进入S期的时间延迟。在这些条件下，内源性细胞周期蛋白E蛋白的表达以及参与G1期转换的其他事件的诱导也延迟。尽管外源性细胞周期蛋白E的表达水平很高，但这些衍生物并未表现出与细胞周期蛋白E相关的体外激酶活性增加。在异步指数分裂和同步细胞群体中，过表达外源性细胞周期蛋白E的HC11细胞中细胞周期蛋白/细胞周期蛋白依赖性激酶抑制剂p27（Kip1）均增加。这些发现表明，HC11细胞中这种细胞周期蛋白E cDNA表达的增加抑制而非刺激生长，这可能是由于抑制剂p27（Kip1）表达增加所致。
