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インドの口腔扁平上皮癌における、p53 と ras 遺伝子変異とタバコとの関連: A. K. Munirajan^1,2, K. Kannan², G. Shanmugam², 土田信夫¹（¹東医歯大 歯 細菌、²Cancer Biology Division, MaduraiKamaraj Univ., India)

Tabaco related mutations in p53 and ras of oral carcinomas from India: A. K. MUNIRAJAN^1,2, K. KANNAN², G. Shanmugam², N. Tsuchida¹ (¹Dept. Mol. Cell. Oncol. & Microbiol., Tokyo Med. & Dent Univ., ²Cancer Biology Div., Madurai Kamaraj Univeristy, India)

In India, tabacco chewing is believed to be an important risk factor in the genesis of oral squamous cell carcinoma. Alkylating agents such as nitrosamine present in chewing tabasso have been implicated in specific G- and T- targeted alterations in the genome. To understand the role of tabcco-related nitrosamines, we analysed 73 tumours for p53 mutations and 46 samples for ras mutations by PCR-SSCP and direct DNA sequencing. The majority (83%) of p53 mutations were G substitution mutations (5G>T and 5G>A) suggesting the involvement of tabacco specific nitrosamines. The same tumour samples were simultatneously subjected to immunohistochemical analysis fo p53 expression. The result showed good correlation with the presence of p53 mutation. Out of the 46 tumours analysed for ras mutation 10 were positive for mutations in codon 12, codon 13 and codon 59 of H-ras and codon 12 of N-ras. In ras too all the mutation targets were G. The effect of tabacco chewing in relation ot p53 and ras mutations will be discussed.