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Expression of retinoic acid receptors in squamous cell carcinomas and their possible implication for chemoprevention.

Retinoic acid and its natural and synthetic analogs (retinoids) affect a wide array of biological processes. Retinoids are used in the treatment of many skin diseases and are promising drugs for several cancers. Most of their actions are thought to result from changes in gene expression which is caused via nuclear retinoic acid receptors and retinoid X receptors. We conducted a study to determine whether the expression of these receptors is different in malignant tumors and tumor cell lines versus normal tissue. We performed reverse transcription PCR from 29 tissue specimens of squamous cell carcinomas and one melanoma of the head and neck, as well as from 13 cell lines established from head and neck cancer. We were looking for the expression pattern of RAR alpha, beta, gamma and RXR alpha. Only RAR gamma was expressed 100% in cell lines and tissue specimens. RAR beta showed 100% expression in tissue specimens whereas 54% expression in cell lines was seen. All other receptors were diminished in their expression. In the positive controls all receptors were expressed at 100%. The expression of RAR alpha and RAR beta was partially lost in cell lines established from squamous cell carcinoma of the head and neck. The 100% expression of RAR beta in tissue samples versus 54% in cell lines can be explained by the clonal growth of malignant cells in cell lines and also possible "contamination" by normal cells in the tissue specimen. In concordance with the literature it seems that RARa and beta play a pivotal role in mediating the response to retinoids.