Treatment of normal human keratinocytes with 2,3,7,8-tetrachlorodibenzo-p-dioxin causes a reduction in cell number, but no increase in apoptosis.

We have examined the effect of TCDD on the growth of normal human keratinocytes. TCDD is a ubiquitous environmental toxicant that causes a severe dermatopathology in humans, which is known as chloracne. The cell biological basis of this pathology remains unknown. We conducted growth experiments in preconfluent normal human keratinocytes with both low (0.05 mM) and standard (0.66 mM) extracellular calcium concentrations in the media. TCDD treatment reduced the number of adherent keratinocytes relative to controls in media containing 0.05 or 0.66 mM calcium. Based on these observations, we speculated that the decrease in the cell number of TCDD-treated cultures might be the result of increased apoptosis. Analysis of nucleosomal fragmentation, nuclear morphology, and caspase-3 activity in keratinocytes reveals no increase in the characteristics of apoptosis in response to TCDD treatment. We therefore conclude that TCDD impacts on keratinocyte homeostasis independent of apoptosis.