Inhibitory effect of tumor suppressor p33(ING1b) and its synergy with p53 gene in hepatocellular carcinoma.

AIM: To investigate the inhibitory effect of tumor suppressor p33(ING1b) and its synergy with p53 gene in hepatocellular carcinoma (HCC). METHODS: Recombinant sense and antisense p33(ING1b) plasmids were transfected into hepatoma cell line HepG2 with lipofectamine. Apoptosis, G0/G1 arrest, cell growth rate and cloning efficiency in soft agar of HepG2 were analyzed after transfection. In three hepatoma cell lines with different endogenous p53 gene expressions, the synergistic effect of p33(ING1b) with p53 was analyzed by flow cytometry and luciferase assay was performed to detect the activation of p53 downstream gene p21(WAF1/CIP1). In addition, the expression and mutation rates of p33(ING1b) in HCC tissues were measured by immunohistochemistry and polymerase chain reaction-single strand conformation polymorphism (PCR-SSCP). RESULTS: Overexpression of p33(ING1b) inhibited cell growth of HepG2, induced more apoptosis and protected cells from growth in soft agar. Combined transfer of p33(ING1b) and p53 gene promoted hepatoma cell apoptosis, G0/G1 arrest and elevated expression of p21(WAF1/CIP1). Immunostaining results showed co-localized P33(ING1b) with P53 protein in HCC tissues and there was a significant relation between protein expression rates of these two genes (P<0.01). Among 28 HCC samples, p33(ING1b) presented a low gene mutation rate (7.1%). CONCLUSION: p33(ING1b) collaborates with p53 in cell growth inhibition, cell cycle arrest and apoptosis in HCC. Loss or inactivation of p33(ING1b) normal function may be an important mechanism for the development of HCC retaining wild-type p53.