Retinoid Regulation of Crabp-II mRNA in an Organotypic Keratinocyte Culture System

Abstract

CRABP-II is selectively and markedly induced by retinoic acid (RA) in adult human skin. However, in submerged, serum-free keratinocyte cultures grown in MCDB 153 medium modified for high-density growth, CRABP-II mRNA could not be induced by RA. Instead, CRABP-II expression was markedly suppressed after prolonged (48 hr) exposure to pharmacologic dosages (3 × 10⁻⁶ M) of RA. The inability of such cultures to induce CRABP-II was not due to the presence of corticosteroids or a lack of extracellular calcium, because CRABP-II responsiveness was not restored by growth of keratinocytes for one passage (about three doublings) in hydrocortisone-free medium, or addition of 2 mM CaCl₂ for 24 hr before RA challenge. Comparisons of intact human skin, submerged keratinocyte cultures, and skin equivalent cultures suggest that induction of CRABP-II by RA requires epidermal stratification, dermal-epidermal interactions, or both. However, the presence of melanocytes, Langerhans cells, mast cells, or endothelial cells is not required. CRABP-II transcripts were undetectable in organotypic skin cultures, as was previously shown to be the case in intact skin, cultured keratinocytes, and cultured fibroblasts. Taken together, these results suggest that organotypic keratinocyte culture systems may provide useful in vitro models for cutaneous responses to RA in vivo.