Human neonatal keratinocytes have very high levels of cellular vitamin A-binding proteins.

Since cellular retinol- and retinoic acid-binding proteins (CRBP and CRABP) mediate the effects of vitamin A on epidermal differentiation, the levels of these binding proteins were measured in the epidermal and dermal layers of newborn, human foreskin as well as in primary cultures of keratinocytes and fibroblasts from these layers. Ligand binding assays with saturating concentrations of all trans-[3H]retinol or of all trans-[11-3H]retinoic acid were used to quantitate amounts of binding proteins in cytosols prepared from these skin layers or cultured cells. The epidermal levels of CRABP and CRBP (60.9 +/- 14.4 and 7.3 +/- 1.7 pmol per mg cytosol protein, respectively) were markedly higher than that reported for adult epidermis but were comparable to levels in keratinocytes cultured from neonatal foreskin epidermis (61.8 +/- 7.8 and 10.7 +/- 2.5, respectively). The levels of CRABP were much lower in the foreskin dermis than in the epidermis and the levels measured in the fibroblasts cultured from this dermis were consistent with the dermal levels. However, CRBP levels in cultured dermal fibroblasts were very low and could not account for the dermal CRBP levels, suggesting that another dermal cell type has high levels of CRBP.