Expression of retinoid-X receptors (-· ,-· ,-·) and retinoic acid receptors (-· ,-· ,-·) in normal human skin: an immunohistological evaluation

Increasing evidence suggests that the retinoid-X receptors (RXR-· ,-· ,-·) play a crucial role in regulating the transcriptional activity of several steroid hormone receptors, including the receptors for retinoic acid (RAR-· ,-· ,-·), 1,25-dihydroxyvitamin D3 and thyroid hormone. We investigated the localization of the different types of RXR-· ,-· ,-· and RAR-· ,-· ,-· proteins in frozen sections of normal human skin (n = 12) in situ, applying recently raised corresponding specific monoclonal antibodies and an immunohistochemical technique that we established for the detection of these nuclear receptors. Our findings indicate that RXR-· ,-· ,-· and RAR-· ,-· ,-· proteins can be detected by immunohistochemistry in normal human skin. In contrast to RXR-· ,-· ,-· as well as RAR-· and RAR-· proteins that were consistently detected in cell layers of the viable epidermis, RAR-· was only focally demonstrated in single epidermal cells in three out of 12 biopsies analysed. Immunohistochemical labelling of RAR-· ,-· ,-· and RXR-· ,-· ,-· proteins in epidermal nuclei was also pronounced in the stratum granulosum, suggesting a function of RXR and RAR proteins in the transition from proliferation to differatiation in epidermal keratinocytes. Expression of RXRs and RARs in hair follicles, sebaceous glands and endothelial cell points to a biological function from these nuclear receptors to hair growth as well as to the physiology of sebaceous glands and endothelial cells.