p16(INK4) gene mutation and allelic loss of chromosome 9p21-22 in Taiwanese hepatocellular carcinoma

Background: The p16(INK4) (MTS1/CDNK2A) gene, located on chromosome 9p21, is an inhibitor of cyclin-dependent kinase 4. Various data have shown that it is frequently inactivated in several types of cell lines and primary human cancers. Materials and Methods: Thirty cases with hepatocellular carcinoma were studied for possible p16(INK4) gene mutation in Taiwan. Homozygous deletion was determined using polymerase chain reaction (PCR). The p16(INK4) gene mutation was first screened by single strand conformation polymorphism, then direct DNA sequencing was performed on the cases with mobility shifts. Deletion mapping of chromosome 9p21-22 was also carried out with two polymorphic microsatellite markers (D9S925 and D9S168) using PCR. Results: One of the 30 cases had homozygous deletion at exon 3 of the p16(INK4) gene. Another tumor had altered electrophoresed mobility in exon 2 with G to T transversion in the first nucleotide of codon 61 by direct sequencing causing a stop codon (GAG→TAG). At the D9S925 and D9S168 loci, six out of 24 (25%) and three out of 19 (16%) informative cases showed loss of heterozygosity, respectively. Conclusion: Point mutation and homozygous deletion of the p16(INK4) gene are present in a subset of hepatocellular carcinomas in Taiwan. The patterns of the p16(INK4) gene alteration are, however, different from those from other regions. In addition, allelic loss on chromosome 9p21-22 is not an uncommon event in hepatocellular carcinomas. Therefore, the significance of chromosome 9p loss deserves to be extensively investigated.