Ladha M H, Lee K Y, Upton T M, Reed M F, Ewen M E
The Dana-Farber Cancer Institute and the Harvard Medical School, Boston, Massachusetts 02115, USA.
Mol Cell Biol. 1998 Nov;18(11):6605-15. doi: 10.1128/MCB.18.11.6605.
The synthesis of cyclin D1 and its assembly with cyclin-dependent kinase 4 (CDK4) to form an active complex is a rate-limiting step in progression through the G1 phase of the cell cycle. Using an activated allele of mitogen-activated protein kinase kinase 1 (MEK1), we show that this kinase plays a significant role in positively regulating the expression of cyclin D1. This was found both in quiescent serum-starved cells and in cells expressing dominant-negative Ras. Despite the observation that cyclin D1 is a target of MEK1, in cycling cells, activated MEK1, but not cyclin D1, is capable of overcoming a G1 arrest induced by Ras inactivation. Either wild-type or catalytically inactive CDK4 cooperates with cyclin D1 in reversing the G1 arrest induced by inhibition of Ras activity. In quiescent NIH 3T3 cells expressing either ectopic cyclin D1 or activated MEK1, cyclin D1 is able to efficiently associate with CDK4; however, the complex is inactive. A significant percentage of the cyclin D1-CDK4 complexes are associated with p27 in serum-starved activated MEK1 or cyclin D1 cell lines. Reduction of p27 levels by expression of antisense p27 allows for S-phase entry from quiescence in NIH 3T3 cells expressing ectopic cyclin D1, but not in parental cells.
细胞周期蛋白D1的合成及其与细胞周期蛋白依赖性激酶4（CDK4）组装形成活性复合物是细胞周期G1期进程中的限速步骤。利用有丝分裂原激活蛋白激酶激酶1（MEK1）的激活等位基因，我们发现该激酶在正向调节细胞周期蛋白D1的表达中起重要作用。这一现象在静止的血清饥饿细胞和表达显性负性Ras的细胞中均被发现。尽管观察到细胞周期蛋白D1是MEK1的一个靶点，但在循环细胞中，激活的MEK1而非细胞周期蛋白D1能够克服由Ras失活诱导的G1期阻滞。野生型或催化失活的CDK4均能与细胞周期蛋白D1协同作用，逆转因Ras活性抑制而诱导的G1期阻滞。在表达异位细胞周期蛋白D1或激活的MEK1的静止NIH 3T3细胞中，细胞周期蛋白D1能够有效地与CDK4结合；然而，该复合物无活性。在血清饥饿的激活MEK1或细胞周期蛋白D1的细胞系中，相当比例的细胞周期蛋白D1 - CDK4复合物与p27相关。通过反义p27的表达降低p27水平，可使表达异位细胞周期蛋白D1的NIH 3T3细胞从静止状态进入S期，但亲代细胞则不能。
