Deletion mutants of the hepatitis B virus X gene in human hepatocellular carcinoma.
Two patients with hepatocellular carcinoma (HCC) were identified who had substantial deletions within the hepatitis B virus (HBV) X gene from HCC tissues. In one patient, the deletion was found at nt. 382-389 (codons 128-130) of the X gene, followed by two nucleotide substitutions, a frame shift, and formation of a new stop codon. In the second patients, the deletion was found at nt. 389-396 (codons 130-132) of the X gene, followed by one nucleotide substitution, a frame shift, and formation of a new stop codon. The resulting X proteins in both cases would be truncated at the 3' end and would be 20 amino acids shorter than the full length X protein. These patients had been identified during a study of 25 HCC patients from Qidong, China in whom a 228-base region of the X gene was sequenced. No deletions were found within this X gene sequence in HCC tissues from the other 23 patients or in the 20 adjacent noncancerous liver samples available from these patients. However, the fact that these deletions encompassed codons 130 and 131, two adjacent codons where point mutations were found in 21 of the remaining 23 patients, suggests that this region may play an important role in hepatocarcinogenesis.