Cancer Research Laboratory and Department of Molecular and Cell Biology, Division of Immunology and Pathogenesis, University of California, Berkeley, California 94720, USA.
J Biol Chem. 2010 Mar 5;285(10):7556-65. doi: 10.1074/jbc.M109.035535. Epub 2010 Jan 12.
Proliferation and apoptosis are diametrically opposite processes. Expression of certain genes like c-Myc, however, can induce both, pointing to a possible linkage between them. Developing CD4(+)CD8(+) thymocytes are intrinsically sensitive to apoptosis, but the molecular basis is not known. We have found that these noncycling cells surprisingly express many cell cycle proteins. We generated transgenic mice expressing a CDK2 kinase-dead (CDK2-DN) protein in the T cell compartment. Analysis of these mice showed that the CDK2-DN protein acts as a dominant negative mutant in mature T cells as expected, but surprisingly, it acts as a dominant active protein in CD4(+)CD8(+) thymocytes. The levels of CDK2 kinase activity, cyclin E, cyclin A, and other cell cycle proteins in transgenic CD4(+)CD8(+) thymocytes are increased. Concurrently, caspase levels are elevated, and apoptosis is significantly enhanced in vitro and in vivo. E2F-1, the unique E2F member capable of inducing apoptosis when overexpressed, is specifically up-regulated in transgenic CD4(+)CD8(+) thymocytes but not in other T cell populations. These results demonstrate that the cell cycle and apoptotic machineries are normally linked, and expression of cell cycle proteins in developing T cells contributes to their inherent 1sensitivity to apoptosis.
增殖和凋亡是截然相反的过程。然而，某些基因的表达，如 c-Myc，可以同时诱导这两种过程，这表明它们之间可能存在联系。正在发育的 CD4(+)CD8(+)胸腺细胞本质上对凋亡敏感，但分子基础尚不清楚。我们发现这些非循环细胞出人意料地表达许多细胞周期蛋白。我们生成了在 T 细胞区室中表达 CDK2 激酶失活 (CDK2-DN) 蛋白的转基因小鼠。对这些小鼠的分析表明，CDK2-DN 蛋白在成熟 T 细胞中如预期的那样作为显性负突变体发挥作用，但令人惊讶的是，它在 CD4(+)CD8(+)胸腺细胞中作为显性激活蛋白发挥作用。转基因 CD4(+)CD8(+)胸腺细胞中的 CDK2 激酶活性、细胞周期蛋白 E、细胞周期蛋白 A 和其他细胞周期蛋白水平增加。同时， caspase 水平升高，体外和体内的凋亡明显增强。E2F-1 是唯一能够过表达诱导凋亡的 E2F 成员，它在转基因 CD4(+)CD8(+)胸腺细胞中特异性上调，但在其他 T 细胞群体中则没有。这些结果表明，细胞周期和凋亡机制通常是相关的，并且发育中的 T 细胞中细胞周期蛋白的表达有助于其对凋亡的固有敏感性。
