Loss of allelic heterozygosity at the harveyras locus in human oral carcinomas

Abstract

The Harveyras locus was examined for restriction fragment polymorphism and loss of allelic heterozygosity in 62 oral cancer patients. Southern blot analysis onBamHI digests of the tumour tissue DNA, revealed 23 patients with H-ras-1 heterozygosity. The probes used to study the polymorphism were theBamHI 6.6-kb fragment encoding the complete H-ras-1 sequence plus the variable tandem repeat (VTR) region, and the 1-kbMspI fragment encoding the VTR region. The allelic heterozygosity was better resolved byPvuII and further confirmed byTaqI. In addition,TaqI digestion demonstrated a unique VTR rearrangement indicated by 2.1-kb, 0.9-kb and 0.6-kb fragments, implying additionalTaqI sites, in three of the patients. Further analysis of matched tumor tissue and peripheral blood cell DNA from the same patient demonstrated tumor-associated loss of one of the allelic fragments in 7/23 (30%) of the patients with H-ras-1 heterozygosity. However, the loss was not significantly correlated to clinicopathological parameters staging the disease. Thus, our data showing loss of H-ras-1 alleles and VTR rearrangement, with relatively high incidence (9/23; 39%) in the oral cancer patients at various stages of the disease, implies H-ras-1 involvement as an early event in the process of oral carcinogenesis.