Epidermal differentiation enhances CRABP II expression in human skin.

The cellular retinoic acid-binding proteins (CRABP I and II) are thought to mediate the effects of retinoic acid on target cells. We have used riboprobes complementary to CRABP I and II mRNAs to study the expression of these messages in normal and abnormal human skin. CRABP II was expressed predominantly in the suprabasal layers of the epidermis, with stronger expression in newborn than in sun-protected adult skin. Interestingly, the epidermis adjacent to or overlying squamous cell or basal cell carcinomas also showed strong expression, whereas the tumor cells were negative, with the exception of more differentiated cells surrounding the "keratin pearls" within squamous cell carcinomas. CRABP II mRNA was also found in the more differentiated cells of the hair follicles, in the outer root sheath. CRABP I message was undetectable in the epidermis or in the dermis of normal skin but was detected in the cells of the papillary dermis surrounding basal and squamous cell carcinomas. These data suggest that increased levels of CRABP II mRNA accompany keratinocyte differentiation in vivo.