Studies on the signal transduction of difrentiation inducing factor and an application for the development of anti-cancer drug for early G_1 phase.

分化诱导因子（DIF）是诱导网骨藻细胞分化的形态发生素。然而，DIF家族的作用并不局限于网骨藻。DIF-1和/或DIF-3在几种哺乳动物细胞中强烈抑制细胞增殖并诱导细胞分化。因此，我们研究了DIF抑制哺乳动物细胞增殖的机制，发现DIF-1和DIF-3通过激活GSK-3β，促进细胞周期蛋白D1的蛋白水解，参与DIF诱导的哺乳动物细胞G_0/G_1期阻滞。我们接下来检查了DIF对细胞周期蛋白D1突变体的影响，发现Thr^的磷酸化<286>对于DIF诱导的细胞周期蛋白D1降解是至关重要的。这些发现表明DIF-1通过GSK-3β介导的Thr β磷酸化诱导细胞周期蛋白D1降解<286>。此外，我们试图确定DIF-1诱导的细胞周期蛋白D1 mRNA表达抑制的机制，发现DIF-1诱导GSK-3β介导的β-catenin降解，导致细胞周期蛋白D1启动子中TCF/LEF转录活性的抑制。此外，我们试图确定GSK-3β中诱导Tyr^磷酸化的激酶<216>，并认为MEK 1/2诱导GSK-3β的酪氨酸磷酸化，这种细胞事件可能诱导GSK-3β的核转位。

Differentiation-inducing factors (DIFs) are morphogens which induce cell differentiation in Dictyostelium. However, the effect of the DIF family is not limited in Dictyostelium. DIF-1 and/or DIF-3 strongly inhibit cell proliferation and induce cell differentiation in several mammalian cells. We therefore investigated the mechanisms for the antiproliferative action of DIFs in mammalian cells.We found that DIFs (DIF-1 and DIF-3) activates GSK-3β to accelerate the proteolysis of cyclin D1 and this mechanism is involved in the DIFs-induced G_0/G_1 arrest in mammalian cells. We next examined the effect of DIFs on cyclin D1 mutants and found that the phosphorylation of Thr^<286> was critical for cyclin D1 degradation induced by DIFs. These findings suggest that DIF-1 induces degradation of cyclin D1 through the GSK-3β-mediated phosphorylation of Thr^<286>. Moreover, we tried to identify the mechanism for the DIF-1-induced suppression of cyclin D1 mRNA expression and found that DIF-1 induces GSK-3β-mediaged degradation of β-catenin, resulting in the suppression of TCF/LEF transcriptional activity in the cyclin D1 promoter.Further, we tried to identify a kinase which induce phosphorylation on Tyr^<216> in GSK-3β and suggested that MEK1/2 induces tyrosine phosphorylation of GSK-3β and this cellular event might induce nuclear translocation of GSK-3β.