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, serum-free medium which facilitated manipulation of their differentiation status. Exposure of basal cell and differentiating cultures to ≥0.1 nm2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) preferentially elevated 7-ethoxyresorufinO-deethylase specific activities in differentiating cultures (28-fold versus 4-fold increases after 36 h of exposure). Semiquantitative reverse-transcription polymerase chain reaction (RT-PCR) analyses demonstrated the presence of constitutive mRNA transcripts corresponding to four known TCDD-inducible genes (e.g.,Cyp1a1, Cyp1b1, Ahd4, andNmo1) in both differentiating and proliferating cultures of murine keratinocytes. All four genes were induced in differentiating cultures following exposure to TCDD. No induction occurred in comparably treated basal cell cultures. Indirect immunofluorescence analyses demonstrated the presence of aryl hydrocarbon receptor (AHR) and aryl hydrocarbon receptor nuclear translocator (ARNT) proteins in both basal and differentiating keratinocytes. Both proteins appeared to be associated with the nucleus and their nuclear association was independent of prior exposure to TCDD. These studies suggest that AHR activation in murine skin is regulated as a function of the keratinocyte differentiation program.