Genetic Predisposition to 4NQO-Induced Tongue Carcinogenesis in the Rat

Objective: This study aims to elucidate the genetic basis of predisposition to 4-nitroquinoline 1-oxide (4NQO)-induced tongue cancers (TCs). Materials and Methods: We have reported that inbred Dark-Agouti (DA) strain rats were highly susceptible to 4NQO-induced TCs, whereas Wistar/Furth (WF) rats were resistant to tongue squamous cell carcinomas induced by oral administration of 4NQO. Using size and number of the tumours as quantitative parameters, responsible host loci were analysed by an interval mapping of F2 intercross of DA and WF given carcinogenic regimen. Also, loss of heterozygosity (LOH) at these loci was analysed in tongue cancers in (DA × WF) F1. Results: We identified and mapped 5 significant quantitative trait loci (QTL), the Tongue squamous cell carcinoma 1–5 (Tscc1–5), and several other suggestive QTL that determine susceptibility to 4NQO-induced TC. Study of TCs induced in (DA × WF)F1 rats revealed a high frequency of LOH in the chromosomal regions of Tscc2, 3, and 4 and also of suggestive QTL on chromosomes 5 and 6. The fact that LOH was found only in larger TCs indicates that LOH occurred in the process of tumour progression. In most LOH, the allele of the resistant WF strain was lost, suggesting that these loci may encode tumour suppressor genes. In larger TCs, in addition to LOH, point mutations and the methylation of possible candidate genes were accumulated. Conclusion: These observations indicate that the 4NQO-induced TC in the rat is a multifactorial disease of a polygenic trait. This model will be useful to understand the complicated genetic basis of predisposition to oral cancers.