Objective: To investigate the effects of tumor suppressor gene PTEN on apoptosis and protein expression of p53 in HepG2 cells, as well as to explore its mechanisms.
Methods: HepG2 cells were transfected with GFP plasmids containing wild-type PTEN or G129E-PTEN and C124A-PTEN in vitro. Both the expression of wild-type p53 and the phosphorylation of protein kinase B (PKB/Akt) and focal adhesion kinase (FAK) were detected by Western blotting. Flow cytometry and confocal microscopy were used to analyze apoptosis of the transfected cells.
Results: Compared with the control, the expression of phosphorylated FAK and phosphoylated Akt were down-regulated in HepG2 cells transfected with wild-type PTEN (-65%, -93%) and G129E-PTEN (-65%, -35%), whereas the apoptosis percentage increased to (19.8+/-1.2)% and (9.2+/-0.6)%, and p53 expression was up-regulated by 120% and 50%, respectively. However, in the cells transfected with C124A-PTEN, neither the phosphorylation of FAK and Akt nor the apoptosis percentage and p53 expression had changed.
Conclusion: PTEN can dephosphrylate FAK through its protein phosphatase activity, and suppress phosphorylation of Akt mainly through its lipid phosphatase activity. Consequently, it can induce apoptosis of HepG2 cells and up-regulate p53 expression.