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


CONCLUSIONS
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.
Zhu
Zhi
Z
Department of Pathology, Changhai Hospital, Second Military Medical University, 174 Changhai Road, Shanghai 200433, China. mhzhu2000@hotmail.com
Lin
Jing
J
Qu
Jian-Hui
JH
Feitelson
Mark-A
MA
Ni
Can-Rong
CR
Li
Fang-Mei
FM
Zhu
Ming-Hua
MH
D017209:Apoptosis / Q000502:physiology; D006528:Carcinoma, Hepatocellular / Q000473:pathology / Q000503:physiopathology*; D018797:Cell Cycle Proteins / Q000378:metabolism; D045744:Cell Line, Tumor; D002470:Cell Survival; D050759:Cyclin-Dependent Kinase Inhibitor p21; D004268:DNA-Binding Proteins; D016193:G1 Phase; D015972:Gene Expression Regulation, Neoplastic; D016147:Genes, Tumor Suppressor; D006801:Humans; D000076023:Inhibitor of Growth Protein 1; D047908:Intracellular Signaling Peptides and Proteins; D008113:Liver Neoplasms / Q000473:pathology / Q000503:physiopathology*; D009687:Nuclear Proteins; D011506:Proteins / Q000235:genetics* / Q000378:metabolism; D016192:Resting Phase, Cell Cycle; D016159:Tumor Suppressor Protein p53 / Q000235:genetics* / Q000378:metabolism; D025521:Tumor Suppressor Proteins
C493956:CDKN1A protein, human; D018797:Cell Cycle Proteins; D050759:Cyclin-Dependent Kinase Inhibitor p21; D004268:DNA-Binding Proteins; C501503:ING1 protein, human; D000076023:Inhibitor of Growth Protein 1; D047908:Intracellular Signaling Peptides and Proteins; D009687:Nuclear Proteins; D011506:Proteins; D016159:Tumor Suppressor Protein p53; D025521:Tumor Suppressor Proteins