Uchida T, Takahashi K, Tatsuno K, Dhingra U, Eliason J F
Department of Oncology, Nippon Roche Research Center, Kamakura, Japan.
Int J Cancer. 1996 Sep 17;67(6):892-7. doi: 10.1002/(SICI)1097-0215(19960917)67:6<892::AID-IJC21>3.0.CO;2-2.
The incidence of hepatocellular carcinoma (HCC) is particularly high in regions of Asia and sub-Saharan Africa where rates of infection with human hepatitis-B virus (HBV) and aflatoxin-B1 contamination of food are high. In HCC tumors occurring in inhabitants of these regions, a G-to-T mutation frequently occurs at position 249 of the tumor-suppressor gene p53. This suggests that HBV and p53 mutation may collaborate in the carcinogenic process in liver. We have examined the effect of the HBV protein HBX in HCC lines with exogenous wild-type p53 or mutated p53 on transactivation of 2 different reporter genes. Transfection of HCC lines with wild-type p53 and a reporter with the promoter from the p53-responsive gene WAF1/p21 resulted in a high level of expression, as expected. When cells were co-transfected with a reporter gene driven by the HBV core promoter and with the HBX gene, expression was enhanced in the Hep 3B, HLE, PLC/PRF/5 and HuH 7 lines, but not in the HuH 1 line. Co-transfection of the reporter with a plasmid containing wild-type p53 resulted in significant inhibition of the HBV core promoter in all of the lines, whereas the mutated p53 gene had no effect. Our results indicate that wild-type p53 can inhibit transcription from the HBV core promoter. In similar experiments, both HBX and p53 were co-transfected into HCC lines with the WAF1/p2l reporter gene. HBX inhibited p53-induced expression in 4 of the 6 lines (Hep 3B, HuH 1, HuH 7 and HLE), there was no effect in one line (HLF), and enhancement was evident in PLC/PRF/5. Our results indicate that inhibition of p53 transcriptional activity by HBX does occur in HCC, but is highly cell-context-dependent. Inhibition of transcription from the HBV core promoter by wild-type p53 appears to be more universal, and may represent a mechanism by which wild-type p53 can protect against the carcinogenic process in liver.
肝细胞癌（HCC）在亚洲和撒哈拉以南非洲地区的发病率特别高，这些地区的人类乙型肝炎病毒（HBV）感染率和食物中的黄曲霉毒素B1污染率都很高。在这些地区居民发生的HCC肿瘤中，肿瘤抑制基因p53的第249位经常发生G到T的突变。这表明HBV和p53突变可能在肝脏致癌过程中协同作用。我们研究了HBV蛋白HBX在具有外源性野生型p53或突变型p53的HCC细胞系中对两种不同报告基因转录激活的影响。正如预期的那样，用野生型p53转染HCC细胞系以及用来自p53反应基因WAF1/p21的启动子的报告基因转染，导致了高水平的表达。当细胞与由HBV核心启动子驱动的报告基因和HBX基因共转染时，Hep 3B、HLE、PLC/PRF/5和HuH 7细胞系中的表达增强，但在HuH 1细胞系中没有增强。将报告基因与含有野生型p53的质粒共转染导致所有细胞系中HBV核心启动子受到显著抑制，而突变型p53基因则没有影响。我们的数据表明野生型p53可以抑制HBV核心启动子的转录。在类似的实验中，HBX和p53都与WAF1/p2l报告基因一起共转染到HCC细胞系中。HBX在6个细胞系中的4个（Hep 3B、HuH 1、HuH 7和HLE）中抑制了p53诱导的表达，在1个细胞系（HLF）中没有影响，而在PLC/PRF/5中则明显增强。我们的数据表明，HBX对p53转录活性的抑制在HCC中确实发生，但高度依赖于细胞背景。野生型p53对HBV核心启动子转录的抑制似乎更具普遍性，并且可能代表了野生型p53可以预防肝脏致癌过程的一种机制。
