Cellular retinoic acid-binding proteins in human epidermis and sebaceous follicles

Evidence suggests that some of the effects of retinoids on sensitive target tissues are mediated by specific cellular binding proteins. This study demonstrated the presence of cellular retinoic acid-binding proteins (cRABP) in human skin. The approximate concentration and affinity of cRABP was determined independently in epidermal and sebaceous follicle cytosol, using both tritiated retinoic acid (RA) and tritiated 13-cis-retinoic acid (13-cis-RA) as radiolabeled ligands. Scatchard analysis suggested that on the basis of binding per mg of cytosol protein, the binding capacities by epidermal and sebaceous follicle cytosol were similar for RA and 13-cis-RA. However, the dissociation constants of binding of 13-cis-RA by sebaceous follicle cRABP was more than 9-fold the Kd for RA (1096 nM compared to 117 nM). The Kd for binding 13-cis-RA by epidermal cRABP was 31-fold the Kd for binding RA (3582 nM compared to 114 nM). Thus the affinity for 13-cis- RA by epidermal and sebaceous follicle cRABP is significantly less than for RA. It appears that the specificity of response of human sebaceous glands to 13-cis-RA is dependent on factors other than the concentration or affinity of cRABP in these structures.