NEUROFIBROMIN - EXPRESSION BY NORMAL HUMAN KERATINOCYTES IN-VIVO AND IN-VITRO AND IN EPIDERMAL MALIGNANCIES

BACKGROUND: Neurofibromin is the product of the NF1 gene, the mutation s of which have been linked with type 1 neurofibromatosis. The express ion of neurofibromin in human skin has not been analyzed in detail. EX PERIMENTAL DESIGN: Polyclonal Ab were raised against synthetic peptide s corresponding to three different sites of neurofibromin. One of the Ah selectively recognized type II neurofibromin. The localization of n eurofibromin was first studied in normal human skin, Further studies c oncentrated on neurofibromin expression in basal cell, and squamous ce ll carcinomas. Reverse transcription-PCR (RT-PCR) and molecular hybrid iz ations and immunocyto chemistry were used to characterize the expre ssion of neurofibromin in cultured keratinocytes. RESULTS: All neurofi bromin-specific Ab immunolabeled the epidermis. The basal keratinocyte s displayed the most prominent immunosignal for type II neurofibromin. RT-PCR demonstrated the presence of both type I and II neurofibromin mRNA transcripts in cultured keratinocytes. Keratinocytes induced to d ifferentiate and to arrest division by a high (1.4 mM) Ca2+ concentrat ion of the culture medium displayed a down-regulation of neurofibromin expression at the mRNA and protein levels. This was most strikingly d emonstrated by a reduction of immunoreactivity for type II neurofibrom in. Basal cell carcinomas displayed a weak immunosignal for type II ne urofibromin. In contrast, particularly the central areas of squamous c ell carcinoma, islands were intensely immunolabeled. CONCLUSIONS: The results suggest that neurofibromin acts as a regulator of the basal ke ratinocytes in normal skin and that cultured keratinocytes offer a hum an model for studies aimed to elucidate the regulation of neurofibromi n gene expression. Furthermore, aberrations in neurofibromin expressio n may play a role in the pathogenesis of epidermal cancers.