| Hepatocellular carcinoma (HCC) is one of the most common cancers in the world, especially in China. Persistent HBV infection and increased exposure to dietary aflatoxin B1 (AFB1) are two major causative factors that are related to HCC occurrence in area of prevalence. Many genetic abnormalities including activated oncogenes, such as the persistently expressed c—myc and TGFα, as well as inactivated tumor suppresser genes, such as p53, are implicated in the occurrence of HCC. Although AFB1 involvement in HCC occurrence has been confirmed in animal models, there is still an unsolved issue regarding its etiological role in human HCC. Molecular epidemiologic data indicated that hotspot mutation of p53 could be induced by AFB1 after long — term HBV infection. However, the pathological effects of the hotspot mutation of p53, postulated to promote hepatocyte growth, is still unknown. Nonetheless, these data provided new clues toward elucidating the mechanism whereby AFB1 causes HCC. In the first part of this study, molecular epidemiological analysis further strengthened and extented the role of AFB1 in the induction of hotspot mutation of the p53 gene. In the second part of this study, in vitro immortalization of rat hepatocyte has been achieved by AFB1 under specific genetic settings.Using asymmetric PCR — direct sequencing, checked by RFLP analysis, the point mutation on codon 249 in exon 7 of the p53 gene was surveyed in 42 DNA samples of HBV positive HCC. Of these 42 samples, 12 were obtained from patients in Beijing, an area of low AFB1 exposure, and 30(12 from 92 and 18 from 93) were from residents of Qidong, a region of high AFB1 exposure. Hotspot mutation frequency for codon 243 were 0/12, 5/12, and 6/18 for samples from Beijing, Qidong in 92, and Qidong in 93, respectively. In the Qidong samples, 7 out of 8 mutations in the third base of codon 249 were G→T transversion, the most common mutation type induced by activated AFB1 in E. coli. Comparison of hotspot mutation frequency of p53 gene between HCC samples from Qidong and Beijing showed that the difference is of high statistical significance. Also, the decreasing trend in the hotspot mutation in the hotspot mutation of p53 in Qidong samples in recent year matches the decreasing exposure of Qidong residents to AFB1 and decreasing mortality... |
