Benaud C M, Dickson R B
Department of Cell Biology, Vincent T Lombardi Cancer Center, Georgetown University Medical Center, 3970 Reservoir Road NW, Washington, DC 20007, USA.
Oncogene. 2001 Jul 27;20(33):4554-67. doi: 10.1038/sj.onc.1204609.
Adhesion to the extracellular matrix is required for the expression and activation of the cyclin-cyclin-dependent kinase (CDK) complexes, and for G1 phase progression of non-transformed cells. However, in non-adherent cells no molecular mechanism has yet been proposed for the cell adhesion-dependent up-regulation of the p27 cyclin-dependent kinase inhibitor (CKI), and the associated inhibition of cyclin E-CDK2. We now show that in epithelial cells the expression of c-Myc is tightly regulated by cell-substrate adhesion. When deprived of adhesion, two independently derived mammary epithelial cell lines, 184A1N4 and MCF-10A, rapidly decrease their level of c-Myc mRNA and protein. This decrease in levels of c-Myc correlates with G1 phase arrest, as indicated by hypophosphorylation of pRb and inhibition of the activity of the cyclin E-CDK2 complex. In 184A1N4 cells, cell-substrate adhesion is required for the suppression of p27, and induction of cyclin E, E2F-1, but not cyclins D1 and D3. Enforced expression of c-Myc in non-adherent 184A1N4 and MCF-10A cells reverses the adhesion-dependent inhibition of cell cycle progression. Restoration of c-Myc in non-adherent cells induces the expression of E2F-1, and hyperphosphorylation of pRb in response to EGF treatment. In addition, expression of c-Myc results in the anchorage-independent activation of the CDK2 complex, the associated upregulation of cyclin E, and the destabilization and degradation of p27 by the ubiquitin-proteasome pathway. Our study thus suggests that c-Myc is the link between cell adhesion and the regulation of p27 and cyclin E-CDK2. Furthermore, we describe a role for c-Myc in adhesion-mediated regulation of E2F-1.
细胞周期蛋白 - 细胞周期蛋白依赖性激酶（CDK）复合物的表达和激活以及非转化细胞的G1期进程需要与细胞外基质黏附。然而，对于非贴壁细胞中p27细胞周期蛋白依赖性激酶抑制剂（CKI）的细胞黏附依赖性上调以及细胞周期蛋白E - CDK2的相关抑制，尚未提出分子机制。我们现在表明，在上皮细胞中，c - Myc的表达受细胞 - 基质黏附的严格调控。当失去黏附时，两个独立衍生的乳腺上皮细胞系184A1N4和MCF - 10A会迅速降低其c - Myc mRNA和蛋白质水平。c - Myc水平的这种降低与G1期停滞相关，如pRb的低磷酸化和细胞周期蛋白E - CDK2复合物活性的抑制所示。在184A1N4细胞中，细胞 - 基质黏附对于p27的抑制以及细胞周期蛋白E、E2F - 1的诱导是必需的，但对细胞周期蛋白D1和D3则不是。在非贴壁的184A1N4和MCF - 10A细胞中强制表达c - Myc可逆转黏附依赖性的细胞周期进程抑制。在非贴壁细胞中恢复c - Myc会诱导E2F - 1的表达，并在EGF处理后导致pRb的过度磷酸化。此外，c - Myc的表达导致CDK2复合物的不依赖贴壁激活、细胞周期蛋白E的相关上调以及通过泛素 - 蛋白酶体途径使p27不稳定和降解。因此，我们的研究表明c - Myc是细胞黏附与p27和细胞周期蛋白E - CDK2调控之间的联系。此外，我们描述了c - Myc在黏附介导的E2F - 1调控中的作用。
