Characterization of Retinoic Acid Receptor-deficient Keratinocytes

Retinoids are essential for normal epidermal growth and differentiation and show potential for the prevention or treatment of various epithelial neoplasms. The retinoic acid receptors (RARα, -β, and -γ) are transducers of the retinoid signal. The epidermis expresses RARγ and RARα, both of which are potential mediators of the effects of retinoids in the epidermis. To further investigate the role(s) of these receptors, we derived transformed keratinocyte lines from wild-type, RARα, RARγ, and RARαγ null mice and investigated their response to retinoids, including growth inhibition, markers of growth and differentiation, and AP-1 activity. Our results indicate that RARγ is the principle receptor contributing to all-trans-retinoic acid (RA)-mediated growth arrest in this system. This effect partially correlated with inhibition of AP-1 activity. In the absence of RARs, the synthetic retinoid N-(4-hydroxyphenyl)-retinamide inhibited growth; this was not observed with RA, 9-cis RA, or the synthetic retinoid (E)-4-[2-(5, 5, 8, 8 tetramethyl-5,6,7,8-tetrahydro-2-naphthalenyl)-1-propenyl] benzoic acid. Finally, both RARα and RARγ differently affected the expression of some genes, suggesting both specific and overlapping roles for the RARs in keratinocytes.