2,3,7,8-Tetrachlorodibenzo-p-dioxin alters the differentiation pattern of human keratinocytes in organotypic culture

Human exposure to the environmental toxin 2,3,7,8-tetrachlorodibenzo-p-diox in (TCDD) produces a severe skin pathology known as chloracne. In these stu dies we employed a three-dimensional, organotypic model system to study the effects of TCDD on human skin. This model uses the spontaneously immortali zed human keratinocyte cell line NIKS and recapitulates both the three-dime nsional microenvironment and epithelial-mesenchymal interactions found in i ntact human skin. Treatment of the organotypic cultures with TCDD causes al terations in the pattern of keratinocyte terminal differentiation. Analysis at both the light and electron microscope levels reveals a fully different iated cornified layer in TCDD-treated organotypic cultures at earlier time points than observed in vehicle (dimethyl sulfoxide)-treated controls. Furt hermore, TCDD-treated organotypic cultures exhibit aberrant distribution of several differentiation-specific protein markers. Basal cells in TCDD- and DMSO-treated organotypic cultures show no differences in proliferation as measured by quantification of 5-bromo-2 ' -deoxyuridine (BrdU)-positive nuc lei. No aberrant BrdU uptake was detected outside of the basal layer. Neith er TUNEL labeling nor immunohistochemical staining with an antibody to acti ve caspase-3 revealed increased apoptosis in TCDD-treated organotypic cultu res relative to controls. These data clearly indicate that TCDD modulates h omeostasis in a model of human stratifying epithelium independent of change s in proliferation and apoptosis, exclusively by impacting keratinocyte ter minal differentiation. This TCDD-induced effect on differentiation-specific proteins results in profound changes in the tissue architecture. (C) 2001 Academic Press.