Evidence has been emerging to suggest that integrin could induce growth inhibition in some cell types. Some of the molecular mechanisms underlying growth arrest have been elucidated. We reported here that overexpression of integrin L1 imposed a growth inhibitory e

Most cell lines are resistant to tumor necrosis factor-a (TNF-a) cytotoxicity and require cotreatment of TNF-a with cycloheximide (Chx) to undergo apoptosis. Recently, the serine/threonine protein kinase, protein kinase B has been demonstrated to protect cells from apoptosis induced by TNF-a. In this study, we have shown that the human hepatocellular carcinoma cell line, SMMC-7721, was insensitive to TNF-a cytotoxicity and underwent apoptosis quickly in the presence of TNF-a and Chx. PKB levels decreased during TNF-a/Chx-induced apoptosis. No significant change in PKB levels was found in the presence of TNF-a or Chx alone. It seemed that the level of PKB closely correlated with apoptosis. The protein level of focal adhesion kinase (FAK) was reduced by 66% by transfecting FAK antisense cDNA recombinant vector into SMMC-7721 cells. We determined the apoptosis-induced effect of TNF-a/Chx on the FAK antisense cDNA transfectant cells. The results indicated that the percentage of apoptotic cells was enhanced at lower doses of TNF-a (10, 20 or 50U: mL21) and decreased at a higher dose of TNF-a (1000 U: mL21) in the transfected cells as compared to the control. Correspondingly, in the FAK antisense cDNA transfectant cells treated with lower doses of TNF-a in presence of 10 mg: mL21 Chx, the PKB level was lower, but in the FAK antisense cDNA transfectants treated with higher doses of TNF-a in presence of 10 mg:mL21 Chx, the PKB level was higher. In response to TNF-a alone, FAK antisense cDNA transfectants showed a decrease in the level of PKB. However, in the case of TNF-a cotreated with wortmannin, a specific inhibitor of phosphatidylinositol 3-kinase (PtdIns3K), the FAK antisense cDNA transfectants produced significantly less amounts of PKB than the control. It seemed that FAK could stimulate PKB levels through a pathway not involving PtdIns3K. These results suggest that FAK can affect the sensitivity of SMMC-7721 cells to TNF-a/Chx-induced apoptosis in a biphasic manner by regulating PKB levels.