Roles of retinoids and their nuclear receptors in the development and prevention of upper aerodigestive tract cancers.

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Abstract
Vitamin A analogs (retinoids) suppress oral and lung carcinogenesis in animal models and prevent the development of second primary tumors in head, neck, and lung cancer patients. These effects result from changes in the expression of genes that regulate cell growth and differentiation. Retinoic acid receptors (RARs; -alpha, -beta, and -gamma) and retinoid X receptors (RXRs; -alpha, -beta, and, -gamma) are retinoid-activated transcription factors, which mediate effects of retinoids on gene expression. Therefore, alterations in receptor expression or function could interfere with the retinoid signaling pathway and thereby enhance cancer development. We found that the expression of RAR beta was suppressed in more than 50% of oral and lung premalignant lesions in individuals without cancer and in dysplastic lesions adjacent to cancer and in malignant oral and lung carcinomas. The expression of the other receptors was not different among normal, dysplastic, and malignant oral tissues. However, the expression of RAR gamma and RXR beta was somewhat decreased in lung cancers. These results show that RAR beta expression is lost at early stages of carcinogenesis in the aerodigestive tract and support the hypothesis that the loss of RAR beta expression may facilitate the development of some of these cancers.