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.