Distribution of catalase and its modulation by 12-O-tetradecanoylphorbol-13-acetate in murine dermis and subpopulations of keratinocytes differing in their stages of differentiation

Topical treatment of female SENCAR mice with 12-O-tetradecanoylphorbol- 13-acetate (TPA) reduced both dermal and epidermal catalase-specific activities 38% and 51% within 6 h and 18 h of promoter application, respectively. Dermal catalase activity recovered to control levels within 72 h of treatment whereas epidermal catalase activity remained suppressed. Activity measurements were also made in four subpopulations of keratinocytes prepared by Percoll gradient centrifugation that differed in their stages of differentiation. Catalase-specific activity increased with keratinocyte maturity and ranged from 45–54 U /mg protein for basal cell preparations to 252 U /mg protein for granular-squamous cell preparations. Pretreatment of the epidermis for 16 –18 h with TPA (2 μg) uniformly reduced catalase-specific activity 46 –52 % in all keratinocyte subpopulations prepared by Percoll gradient centrifugation. Similarly, plots of catalase units per cell versus extracted protein per cell suggested 55 –60 % decreases in catalase activity in basal and spinous cell keratinocytes of TPA treated epidermis. Furthermore, catalase-specific activity in homogenates of whole epidermis (144 –182 units /mg protein) was most similar to the activity of the granular/squamous keratinocyte subpopulation. Collectively, these studies suggest that: (i) TPA reduces the capacity for H2O2 detoxification by catalase throughout the epidermis; and (ii) activity measurements on unfractionated epidermal preparations may not be representative of the basal cell keratinocyte population.