Objective: To investigate the relationship between alterations of p16(INK4a) and p14(ARF) genes and gastric carcinogenesis.
Methods: The tumors and neighboring gastric tissues from 48 patients with gastric cancer were studied. The homozygous deletion, mutation, methylation of the CpG islands, and mRNA expression of p16(INK4a) and p14(ARF) genes were assessed by PCR, PCR-SSCP, PCR based methylation assay, and RT-PCR.
Results: (1) The homozygous deletion rate of p16(INK4a) and p14(ARF) was 35.4% (17/48), and no homozygous deletion was examined in any gastric tissue neighboring the tumor. (2) There was no point mutation of p16(INK4a) and p14(ARF) in 31 gastric cancers without homozygous deletion or in the matched gastric tissues adjacent to the tumor. (3) Methylation of the CpG islands of p16(INK4a) and p14(ARF) was detected in 47.9% (23/48) of gastric cancers, while methylation was observed only in 2 of 48 gastric tissues neighboring the cancer with a significant difference (P < 0.01). (4) The loss rate of p16(INK4a) mRNA was 47.9% (23/48) in gastric cancer, and the patients of the combined methylation of exons 1alpha and 2 had a higher loss rate (100%, 6/6) of p16(INK4a) mRNA than those of the methylation of the other exons (11.8%, 2/17, P < 0.01); the loss rate of p14(ARF) mRNA was 45.8% (22/48) in gastric cancer, and patients with the combined methylation of exons 1beta and 2 had a higher loss rate (100%, 3/3) of p14(ARF) mRNA than those of the methylation of the other exons (15%, 3/20, P < 0.05). (5) The combined loss of p16(INK4a) and p14(ARF) mRNAs was examined in 1 (5.6%) of 18 patients of well and moderately-differentiated carcinomas, and 11 (36.7%) of 30 patients of poorly and not-differentiated carcinomas with a significant difference (P < 0.05).
Conclusion: p16(INK4a) and p14(ARF) genes are frequently inactivated by homozygous deletion and methylation of the 5'CpG islands in gastric cancer, which may play an important role in the carcinogenesis of gastric cancer.