DIFFERENTIATION STATUS OF CULTURED MURINE KERATINOCYTES MODULATES INDUCTION OF GENES RESPONSIVE TO 2,3,7,8-TETRACHLORODIBENZO-P-DIOXIN

Primary murine keratinocytes were cultured in a chemically defined, se rum-free medium which facilitated manipulation of their differentiatio n status. Exposure of basal cell and differentiating cultures to great er than or equal to 0.1 nM 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) preferentially elevated 7-ethoxyresorufin O-deethylase specific activi ties in differentiating cultures (28-fold versus Li-fold increases aft er 36 h of exposure). Semiquantitative reverse-transcription polymeras e chain reaction (RT-PCR) analyses demonstrated the presence of consti tutive mRNA transcripts corresponding to four known TCDD-inducible gen es (e.g., Cyp1a1, Cyp1b1, Ahd4, and Nmo1) in both differentiating and proliferating cultures of murine keratinocytes. All four genes were in duced in differentiating cultures following exposure to TCDD, No induc tion occurred in comparably treated basal cell cultures, Indirect immu nofluorescence analyses demonstrated the presence of aryl hydrocarbon receptor (AHR) and aryl hydrocarbon receptor nuclear translocator (ARN T) proteins in both basal and differentiating keratinocytes. Both prot eins appeared to be associated with the nucleus and their nuclear asso ciation was independent of prior exposure to TCDD, These studies sugge st that AHR activation in murine skin is regulated as a function of th e keratinocyte differentiation program. (C) 1997 Academic Press.