Focusing in on P53 in hepatocellular carcinoma

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Abstract

Human hepatocellular carcinomas (HCC) from patients in Qidong, an area of high incidence in China, in which both hepatitis B virus and aflatoxin B1 are risk factors, were analysed for mutations in p53, a putative tumour-suppressor gene. Eight of the 16 HCC had a point mutation at the third base position of codon 249. The G→T transversion in seven HCC DNA samples and the G→C transversion in the other HCC are consistent with mutations caused by aflatoxin B1 in mutagenesis experiments. No mutations were found in exons 5, 6, 8 or the remainder of exon 7. These results contrast with p53 mutations previously reported in carcinomas and sarcomas of human lung, colon, oesophagus and breast; these are primarily scattered over four of the five evolutionarily conserved domains, which include codon 249. We suggest that the mutant p53 protein may be responsible for a selective clonal expansion of hepatocytes during carcinogenesis.

Bressac B, Kew M, Wands J, Ozturk M. Selective G to T mutations of p53 gene in hepatocellular carcinoma from southern Africa. Nature 1991;350:429–431.

Hepatocellular carcinoma (HCC) is a prevalent cancer in sub-Saharan Africa and eastern Asia. Hepatitis B virus and aflatoxins are risk factors for HCC, but the molecular mechanism of human hepatocellular carcinogenesis is largely unknown. Abnormalities in the structure and expression of the tumour-suppressor gene p53 are frequent in HCC cell lines, and allelic losses from chromosome 17p have been found in HCCs from China and Japan. Here we report on allelic deletions from chromosome 17p and mutations of the p53 gene found in 50% of primary HCCs from southern Africa. Four of five mutations detected were G→T substitutions, with clustering at codon 249. This mutation specificity could reflect exposure to a specific carcinogen, one candidate being aflatoxin B1, a food contaminant in Africa, which is both a mutagen that induces G to T substitution and a liver-specific carcinogen.

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