AIM:To clarify the mechanisms of integrin overexpressionin negatively regulating the cell cycle control of hepatocellularcarcinoma cells SMMC-7721.METHODS:The cell cycle pattern was determined by flowcytometry.The mRNA and protein expression levels wereassayed by RT-PCR and Western blot,respectively.Stabletransfection was performed by Lipofectamine 2000 reagent,and ceils were screened by G418.RESULTS:Overexpression of α5β1 or β1 integrin inducedS-phase delay in SMMC-7721 cells,and this delay waspossibly due to the accumulation of cyclin-dependent kinaseinhibitors (CKIs) p21~(cip1) and p27~(kip1).The decrease of proteinkinase B (PKB) phosphorylation was present in this signalingpathway,but focal adhesion kinase (FAK) was not involved.When phosphorylation of PKB was solely blocked bywortmannin,p27~(kip1) protein level was increased.Moreover,S-phase delay was recurred when attachment of the parentalSMMC-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 integrin pi subunit is attributed to the decrease of PKB phosphorylation and subsequent increases of p21~(dpl) and p27~(Wpi) proteins, and may be involved in the unoccupied ocBpl because of lack of its ligands. AIM: To clarify the mechanisms of integrin overexpression in negatively regulating the cell cycle control of hepatocellular carcinoma cells SMMC-7721. METHODS: The cell cycle pattern was determined by flow cytometry. The mRNA and protein expression levels wereassayed by RT-PCR and Western blot, respectively. Stabletransfection was performed by Lipofectamine 2000 reagent, and ceils were screened by G418. RESULTS: Overexpression of α5β1 or β1 integrin induced S-phase delay in SMMC-7721 cells, and this delay was postponed to the accumulation of cyclin-dependent kinase inhibitors (CKIs) p21 The decrease of proteinkinase B (PKB) phosphorylation was present in this signaling pathway but focal adhesion kinase (FAK) was not involved. Phosphorylation of PKB was partially 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 patter n was similar to that of β1-7721 or α5β1-7721 cells. CONCLUSION: S-phase delay induced by overexpression of integrin pi subunit is attributed to the decrease of PKB phosphorylation and subsequent increases of p21 ~ (dpl) and p27 ~ (Wpi ) proteins, and may be involved in the unoccupied ocBpl because of lack of its ligands.