Integrin β1A Upregulates p27 Protein Amount at the Post-translational Level in Human Hepatocellular Carcinoma Cell Line SMMC-7721

摘要

Integrins mediate many fundamental cellular processes by binding to components of the extracellular matrix. We showed previously that integrin β1A could inhibit cell proliferation. Integrin β1A stimulated the promoter activity of p21cip1 and enhanced its transcription in SMMC-7721 cells. In this study,we demonstrated that integrin β1A upregulated p27kip1 at the post-translational level in SMMC-7721 cells. Our results showed that integrin β1A increased the p27 protein amount, both in cytoplasm and nucleus, but did not affect the p27m RNA amount. Cycloheximide treatment experiment revealed that the half-life of p27 protein was prolonged in integrin β1A overexpressing cells, indicating that integrin β1A 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 β1A decreased the Skp2 expression and repressed the activity of calpain during G1 phase in SMMC-7721 cells. Taken together, these results indicated that integrin β1A might upregulate the protein amount of p27 through repressing Skp2-dependent proteasome degradation and calpainmediated proteolysis in SMMC-7721 cells.