MODULATION OF CATALASE ACTIVITIES IN MURINE EPIDERMAL-CELLS AS A FUNCTION OF DIFFERENTIATION AND EXPOSURE TO 12-O-TETRADECANOYLPHORBOL-13-ACETATE

A procedure was developed for the per cell estimation of catalase activities in suspensions and cultures of murine epidermal keratinocytes (MEKs). Per cell catalase activity in MEKs cultured in low Ca2+ medium was relatively constant during the proliferation phase of culturing, but increased ̃100% within 24 h of cessation of cell division. 12-O-Tetradecanoylphorbol-13-acetate (TPA) treatment of proliferating MEKs cultured in low Ca2+ medium resulted in (i) an initial suppression of proliferation, (ii) the accelerated detachment and differentiation of detached MEKs and (iii) a suppression of catalase induction in the detached population. Induction of MEK differentiation by raising the medium Ca2+ concentration resulted in rapid inhibition of cell division and ̃200% increases in per cell catalase activities. Addition of TPA immediately prior to Ca2+ shift completely suppressed the Ca2+-dependent increases in activity. However, the addition of TPA 48 h after the induction of differentiation by Ca2+ shift had no effects on the elevated, pre-existing catalase activities. Per cell catalase activities varied in vivo with the stage of MEK differentiation. Specifically, the lowest and highest per cell activities (̃4-fold difference) were measured in enriched basal cell and spinous cell populations respectively. Catalase activity in the more differentiated MEKs was reduced ̃33% within 24 h of topical treatment of dorsal skin with a promoting dose of TPA. However, catalase activity in enriched basal cell preparations was unaffected. Collectively, these studies demonstrate that per cell catalase activities increase as MEKs differentiate, and that TPA suppresses the increases in catalase activities that normally occur during differentiation. © 1990 Oxford University Press.