Department of Biology, McMaster University, 1280 Main St. West, Hamilton, Ontario L8S 4K1, Canada.
J Virol. 2011 Jul;85(13):6725-35. doi: 10.1128/JVI.01013-10. Epub 2011 Apr 20.
The activation of AP-1 is a hallmark of cell transformation by tyrosine kinases. In this study, we characterize the role of AP-1 proteins in the transformation of chicken embryo fibroblasts (CEF) by v-Src. In normal CEF, the expression of a dominant negative mutant of c-Jun (TAM67) induced senescence. In contrast, three distinct phenotypes were observed when TAM67 was expressed in v-Src-transformed CEF. While senescent cells were also present, the inhibition of AP-1 caused apoptosis in a fraction of the v-Src-transformed cells. In addition, cells containing lipid-rich vesicles accumulated, suggesting that a subpopulation of the v-Src-transformed cells underwent differentiation in response to the inhibition of AP-1. JunD and Fra-2 were the main components of this factor, while c-Jun accounted for a minor fraction of AP-1 in v-Src-transformed CEF. The downregulation of c-Jun expression by short hairpin RNA (shRNA) induced senescence in normal and v-Src-transformed cells. In contrast, a high incidence of apoptosis was caused by the downregulation of JunD, suggesting that it is required for the survival of v-Src-transformed CEF. Levels of the p53 tumor suppressor were elevated under conditions of JunD inhibition. Repression of p53 by shRNA enhanced the survival and anchorage-independent proliferation of v-Src-transformed CEF with JunD/AP-1 inhibition. The inhibition of Fra-2 had no visible phenotype in normal CEF but caused the appearance of lipid-rich vesicles in v-Src-transformed CEF. Therefore, AP-1 facilitated transformation by acting as a survival factor, by inhibiting premature entry into senescence, and by blocking the differentiation of v-Src-transformed CEF.
AP-1 的激活是酪氨酸激酶使细胞转化的标志。在这项研究中，我们研究了 AP-1 蛋白在 v-Src 转化鸡胚成纤维细胞（CEF）中的作用。在正常 CEF 中，表达显性失活的 c-Jun 突变体（TAM67）会诱导衰老。相比之下，当 TAM67 在 v-Src 转化的 CEF 中表达时，观察到三种不同的表型。虽然仍存在衰老细胞，但 AP-1 的抑制导致一部分 v-Src 转化细胞发生凋亡。此外，富含脂质的囊泡积累的细胞也存在，表明 v-Src 转化细胞的一个亚群对 AP-1 的抑制发生了分化。JunD 和 Fra-2 是该因子的主要成分，而 c-Jun 在 v-Src 转化的 CEF 中仅占 AP-1 的一小部分。短发夹 RNA（shRNA）下调 c-Jun 的表达会诱导正常和 v-Src 转化细胞衰老。相反，JunD 的下调会导致较高的凋亡发生率，表明它是 v-Src 转化的 CEF 存活所必需的。在 JunD 抑制的条件下，p53 肿瘤抑制因子的水平升高。shRNA 抑制 p53 增强了 JunD/AP-1 抑制时 v-Src 转化的 CEF 的存活和非锚定依赖性增殖。Fra-2 的抑制在正常 CEF 中没有明显的表型，但在 v-Src 转化的 CEF 中会导致富含脂质的囊泡出现。因此，AP-1 通过作为生存因子、抑制过早进入衰老和阻止 v-Src 转化的 CEF 分化来促进转化。
