Fu Yi, Wang Li-Ying, Liang Yu-Long, Jin Jia-Wei, Fang Zheng-Yu, Zha Xi-Liang
Department of Biochemistry and Molecular Biology, Shanghai Medical College, Fudan University, Shanghai 200032, China.
Acta Biochim Biophys Sin (Shanghai). 2006 Aug;38(8):523-30. doi: 10.1111/j.1745-7270.2006.00201.x.
Integrins mediate many fundamental cellular processes by binding to components of the extracellular matrix. We showed previously that integrin beta(1A) could inhibit cell proliferation. Integrin beta(1A) stimulated the promoter activity of p21(cip1) and enhanced its transcription in SMMC-7721 cells. In this study, we demonstrated that integrin beta(1A) upregulated p27(kip1) at the post-translational level in SMMC-7721 cells. Our results showed that integrin beta(1A) increased the p27 protein amount, both in cytoplasm and nucleus, but did not affect the p27 mRNA amount. Cycloheximide treatment experiment revealed that the half-life of p27 protein was prolonged in integrin beta1A overexpressing cells, indicating that integrin beta(1A) inhibited the degradation of p27 protein. Our data also provided evidence that both the proteasome and calpain were involved in the degradation of p27 protein in SMMC-7721 cells. Integrin beta(1A) decreased the Skp2 expression and repressed the activity of calpain during G1 phase in SMMC-7721 cells. Taken together, these results indicated that integrin beta(1A) might upregulate the protein amount of p27 through repressing Skp2-dependent proteasome degradation and calpain-mediated proteolysis in SMMC-7721 cells.
整合素通过与细胞外基质成分结合来介导许多基本的细胞过程。我们之前表明整合素β(1A)可以抑制细胞增殖。整合素β(1A)刺激了p21(cip1)的启动子活性并增强其在SMMC - 7721细胞中的转录。在本研究中，我们证明整合素β(1A)在SMMC - 7721细胞的翻译后水平上调p27(kip1)。我们的结果表明整合素β(1A)增加了细胞质和细胞核中p27蛋白的量，但不影响p27 mRNA的量。环己酰亚胺处理实验表明在整合素β1A过表达的细胞中p27蛋白的半衰期延长，表明整合素β(1A)抑制了p27蛋白的降解。我们的数据还提供了证据表明蛋白酶体和钙蛋白酶都参与了SMMC - 7721细胞中p27蛋白的降解。在SMMC - 7721细胞的G1期，整合素β(1A)降低了Skp2的表达并抑制了钙蛋白酶的活性。综上所述，这些结果表明整合素β(1A)可能通过抑制SMMC - 7721细胞中Skp2依赖的蛋白酶体降解和钙蛋白酶介导的蛋白水解来上调p27的蛋白量。
