Splicing mutations of the p53 gene in human hepatocellular carcinoma.
Point mutations in exons of the tumor suppressor p53 gene occur frequently in many human tumors including hepatocellular carcinoma and are extensively studied. However, intronic point mutations are rare and are totally unknown for hepatocellular carcinoma. By reverse transcription and polymerase chain reaction amplification of p53 RNA from hepatocellular carcinoma tissues of 45 Taiwanese patients, we found amplified complementary DNA fragments of abnormal size in 4 (9%) tumor samples. Sequence analysis of these complementary DNA products revealed aberrant retention of intron 7 in one sample, insertion of 49 base pairs of the 3' end of intron 6 in 2 samples, and deletion of exon 4 in the other sample. Direct sequencing of their genomic DNA revealed relevant point mutations at consensus sequence at either the 5' or 3' splice site of intron 7, 6, 6, and 3, respectively. The splicing mutations produced p53 mutants with truncation of COOH-terminus that are identical to those found in lung cancers. Three of the 4 patients with splicing mutations were younger and had huge tumors. The results suggest a possible role of these p53 mutants in the development of human cancers.