S-phase delay in human hepatocellular carcinoma cells induced by overexpression of integrin β1

AIM: To clarify the mechanisms of integrin overexpression in negatively regulalting the cell cyde control of hepatocellular carcinoma cells SMMC-7721.METHODS: The cell cycle pattern was determined by flow cytometry. The mRNA and protein expression levels were assayed by RT-PCR and Western blot, respectively. Stable transfection was performed by Upofectamine 2000 reagent,and cells were screened by G418.RESULTS: Overexpression of α5β1 or β1 integrin induced S-phase delay in SMMC-7721 cells, and this delay was possibly due to the accumulaltion of cydin-dependent kinase inhibitors (CKIs) p21^cip1 and p27^kip1. The decrease of protein kinase B (PKB) phosphorylation was present in this signaling pathway, but focal adhesion kinase (FAK) was not involved.When phosphorylation of PKB was solely blocked by wortmannin, p27^kip1 protein level was increased. Moreover,S-phase delay was recurred when attachment of the parental SMMC-7721 cells was inhibited by the preparation of poly-HEME, and this cell cycle pattern was similar to that of β1-7721 or α5β1-7721 cells.CONCLUSION: S-phase delay induced by overexpression of integdn 151 subunit is attributed to the decrease of PKB phosphorylation and subsequent increases of p21^cip1 and p27^kip1 proteins, and may be involved in the unoccupied α5β1 because of lack of its ligands.