No point mutation but decreased expression of the p16/MTS1 tumor suppressor gene in nasopharyngeal carcinomas.

Nasopharyngeal carcinoma (NPC) is a malignancy which occurs at high incidence in southern China and southeast Asia. The molecular mechanism of this disease, however, is not well understood. Recently, a homozygous deletion and/or loss of heterozygosity on chromosome 9p21-22 was found in several primary NPCs (Huang et al., Cancer Res. 54: 4003-4006, 1994), suggesting that a potential tumor suppressor gene(s) residing in this region may play a role in nasopharyngeal carcinogenesis. Since p16/MTS1, a potential tumor suppressor gene, whose mutations/deletions are frequently found in variety of tumor cells, was mapped to chromosome 9p21, we investigated the possible involvement of this gene in the development of NPC by mutational and Northern blot analysis. SSCP-direct sequencing revealed no point mutations of the p16/MTS-1 gene in any of 42 primary NPC biopsies from three geographical regions nor in two NPC cell lines. We did, however, observe a codon 140ala-->thr polymorphism in the gene, which has been previously reported as a point mutation. Furthermore, Northern analysis revealed a decreased expression of the p16/MTS1 gene in two out of two NPC cell lines as compared with immortalized/nontransformed cell lines. These results suggest that down regulation rather than a point mutation of the p16/MTS1 gene may play a role in the genesis of NPC.