Increased expression of the insulin-like growth factor I (IGF-I) receptor gene in hepatocellular carcinoma cell lines: implications of IGF-I receptor gene activation by hepatitis B virus X gene product.
Hepatitis B virus infection is associated with acute and chronic liver disease and the development of hepatocellular carcinoma (hcc). Several lines of evidence have suggested that hepatitis B virus X protein (HBx), which is a transcriptional trans-activator, plays a role in the process of liver carcinogenesis. We have investigated the expression of insulin-like growth factor I (IGF-I) receptor in human hepatocellular carcinoma cell lines using SNU368 cells containing HBx and SNU387 cells, which lack HBx gene transcript (J-G. Park et al., Int. J. Cancer, 62: 276-282, 1995), in an attempt to understand its possible relationship to the HBx-induced hcc. The binding of 125I-labeled IGF-I to the SNU368 cells was 5-fold higher than that of SNU387 cells. The Scatchard analysis of the binding data revealed a single class binding site for IGF-I with Kd of 7.6 and 8.8 nM and maximum binding capacities of 169 and 33 fmol/10(5) cells, respectively. Therefore, the difference observed in 125I-labeled IGF-I binding between SNU368 and SNU387 cells was due to an increase in the number of IGF-I binding sites with no change in affinity for the IGF-I receptor. An enhanced level of IGF-I receptors in SNU368 cells was also observed by fluorescence-activated cell sorting analysis using a monoclonal antibody against human IGF-I receptor, alpha IR3. The level of IGF-I receptor RNA and the basal IGF-I receptor gene promoter activity in SNU368 cells were 5 and 10 times higher than those observed in SNU387 cells, respectively. To substantiate further that HBx could transactivate the expression of the endogenous IGF-I receptor gene, Hep G2 cells were transiently transfected with a HBx expression vector. The transfection of Hep G2 cells with an HBx expression vector resulted in increased levels of IGF-I receptor RNA, promoter activity, and 125I-labeled IGF-I binding by 2.6-, 2.8-, and 2-fold, respectively. As a result of higher levels of IGF-I receptor, the mitogenic effect of IGFs (IGF-I and IGF-II) on SNU368 cells was 6 times higher than that of SNU387 cells. These results suggest that HBx may play a role in the process of hcc by activating IGF-I receptor gene expression.
Kim
S O
SO
Molecular Cell Biology Research Division, Korea Research Institute of Bioscience and Biotechnology, KIST, Yusong, Taejon, Korea.
Park
J G
JG
Lee
Y I
YI
D006528:Carcinoma, Hepatocellular / Q000378:metabolism*; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D008113:Liver Neoplasms / Q000378:metabolism*; D017526:Receptor, IGF Type 1 / Q000235:genetics*; D013002:Somatomedins / Q000494:pharmacology; D015534:Trans-Activators / Q000235:genetics / Q000502:physiology*; D015533:Transcriptional Activation; D014162:Transfection; D014407:Tumor Cells, Cultured; D054334:Viral Regulatory and Accessory Proteins
D013002:Somatomedins; D015534:Trans-Activators; D054334:Viral Regulatory and Accessory Proteins; C057628:hepatitis B virus X protein; D017526:Receptor, IGF Type 1