REGULATION OF RETINOIC ACID RECEPTOR EXPRESSION IN DERMAL FIBROBLASTS

Retinoic acid (RA) is known to exert profound effects on growth and di fferentiation in a variety of cell types in the skin. In vitro studies have also shown that RA modulates gene expression in both fibroblasts and keratinocytes. Recently, three nuclear receptors specific for ret inoic acid (RAR alpha, RAR beta, and RAR gamma) have been cloned and a ll are members of a large multigene family of ligand-inducible transcr iption enhancer factors. As a first step in defining the role of each receptor in the retinoid response of the skin, we examined the regulat ion of RAR alpha, RAR beta, and RAR gamma gene expression in human der mal fibroblasts by all-trans-retinoic acid. We demonstrate that human dermal fibroblasts express modest basal levels of RAR alpha and RAR ga mma, but not RAR beta. When treated with 1 mu M RA, the messenger RNAs for both RAR beta and RAR gamma are induced. In contrast, RAR alpha r emains unchanged. The induction of RAR gamma is attenuated by the prot ein synthesis inhibitor, cycloheximide, while the induction of RAR bet a increases slightly. Studies with actinomycin D and cycloheximide sho w that all three receptors have different half-lives, with RAR gamma h aving the longest half-life at 8 h. Gel shift analysis of known retino ic acid response elements (RAREs) in the RAR beta and RAR gamma genes demonstrates that the upregulation of these by genes by RA involves in creased binding of complexes to the individual RAREs. In summary, thes e data demonstrate that fibroblasts express all three receptor types. Moreover, striking differences exist in the regulation of RAR gene exp ression in skin-derived fibroblasts and suggest that each receptor may well have a separate and discrete function in the retinoid response o f the skin. (C) 1994 Academic Press, Inc.