Overexpression of integrin β1 inhibits proliferation of hepatocellular carcinoma cell SMMC‐7721 through preventing Skp2‐dependent degradation of p27 via PI3K pathway

Abstract Integrins may play important roles in many cellular events, such as cell proliferation, differentiation, and apoptosis. We showed previously that overexpression of integrin β1 inhibits cell proliferation in SMMC‐7721 cells. Here we reported that one of the cyclin‐dependent kinase (CDK) inhibitors, p27 Kip1 was involved in proliferation–inhibition induced by overexpression of integrin β1. Overexpression of integrin β1 upregulated p27 Kip1 at the protein level, but not mRNA level. The knock‐down of p27 Kip1 expression restored cell growth in integrin β1‐overexpressing cells. Cycloheximide (Chx) treatment and pulse‐chase experiments revealed that overexpression of integrin β1 prolonged the half‐life of p27 Kip1 by inhibiting its degradation. Proteasome inhibitor (MG132) treatment of the cells indicated that proteasome mediated degradation of p27, and Skp2‐dependent degradation might be prevented. Overexpression of integrin β1 decreased Skp2 at mRNA level, which was regulated by cell adhesion and the subsequent adhesion‐dependent signaling. Overexpression of integrin β1 reduced cell adhesion, accordingly, inactivated the phosphoinositide 3‐kinase (PI3K) signaling. PI3K inhibitor LY294002 upregulated p27 Kip1 at post‐translational level and downregulate Skp2 at mRNA level, which could mimic the effects of integrin β1 overexpression on p27 Kip1 and Skp2. Together, these results suggested that overexpression of integrin β1 inhibited cell proliferation by preventing the Skp2‐dependent degradation of p27 Kip1 via PI3K pathway. J. Cell. Biochem. 102: 704–718, 2007. © 2007 Wiley‐Liss, Inc.