( ¹ Department of Biochemistry and Molecular Biology, Ministry of Public Health Key Laboratory of
Glycoconjugate Research, Fudan University Shanghai Medical College, Shanghai 200032, China;
² Department of Biochemistry, Tongji University School of Medicine, Shanghai 200092, China;
³ The Pulmonary Center and Department of Biochemistry, Boston University Medical Center, Boston, MA 02118, USA )

Abstract PTEN is a major tumor suppressor gene that encodes a dual-specificity phosphatase with high sequence similarity to the cytoskeletal protein tensin. PTEN may be involved in the formation and disassembly of focal adhesion and affect cell migration. In the present study, PTEN expression plasmid was constructed and transfected into the hepatoma cell line SMMC-7721 to analyze the alterations of cell motility and FAK tyrosine phosphorylation. It was observed that the overexpression of PTEN gene significantly inhibited cell motility on extracellular matrix (Fn), and the cell migration on fibronectin was reduced by 35%. Similarly, at 30-min and 60-min, the cell spreading on Fn but not on polylysine was inhibited by 29% and 26% respectively. The data obtained from immunoprecipitation and immunoblotting analyses showed that the overexpression of PTEN did not affect FAK expression but resulted in a decrease in FAK tyrosine phosphorylation. The level of FAK phosphorylation was inversely correlated with the level of PTEN protein in three cell lines. It was also found that the overexpression of PTEN led to growth inhibition, with the number of cells in S phase reduced by 16%. These results indicate that PTEN exerts its tumor-suppressive effects on hepatocellular carcinoma cells through the inhibition of cell motility and cell cycle progression.