title: Modulation of constitutive cytochrome P-450 expression in vivo and in vitro in murine keratinocytes as a function of differentiation and extracellular Ca2+ concentration.
abstract: A procedure was developed for the per cell estimation of cytochrome P-450-dependent monooxygenase activities in cultures and whole cell suspensions of murine epidermal keratinocytes (MEKs). Murine keratinocytes cultured in medium containing less than or equal to 0.04 mM Ca2+ can be induced to differentiate by raising medium Ca2+ concentrations to 1.2 mM. The per cell activities of the monooxygenases 7-ethoxyresorufin O-deethylase (7-ER) and 7-ethoxycoumarin O-deethylase (7-EC) were elevated greater than or equal to 2090% and approximately 460%, respectively, within 13-24 hr of Ca2+ shift. These increases could be completely suppressed by supplementation of culture medium with actinomycin D or cycloheximide immediately prior to Ca2+ shift. After prolonged culture in low Ca2+ medium, some MEKs detached from the monolayer. These detached cells had the characteristics of differentiating MEKs but did not have elevated 7-EC or 7-ER activities. Percoll gradient centrifugation of freshly isolated dorsal skin MEKs was used to prepare four subpopulations that differed in their stages of terminal differentiation. 7-EC and 7-ER activities varied among these subpopulations and correlated with the degree of MEK differentiation. Specifically, the lowest and highest per cell activities (greater than 7-fold difference) were in the basal and most differentiated spinous cell populations, respectively. Collectively, the current studies demonstrate that in vivo P-450 activities are markedly different in proliferating and differentiating MEKs and suggest that constitutive P-450 expression may be modulated as a function of changes in Ca2+ concentration that occur during keratinocyte terminal differentiation.
authors.affiliation: University of Texas M.D. Anderson Cancer Center, Science Park-Research Division, Smithville 78957.
authors.forename: J J
authors.initials: JJ
authors.lastname: Reiners
authors.forename: A R
authors.initials: AR
authors.lastname: Cantu
authors.forename: A
authors.initials: A
authors.lastname: Pavone
mesh_terms: D000818:Animals; D002118:Calcium / Q000494:pharmacology*; D002454:Cell Differentiation; D002469:Cell Separation; D002478:Cells, Cultured; D003513:Cycloheximide / Q000494:pharmacology; D003577:Cytochrome P-450 Enzyme System / Q000096:biosynthesis*; D003609:Dactinomycin / Q000494:pharmacology; D004790:Enzyme Induction; D005260:Female; D015603:Keratinocytes / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D051379:Mice; D008815:Mice, Inbred Strains; D006899:Mixed Function Oxygenases / Q000096:biosynthesis
chemical_list: D003609:Dactinomycin; D003577:Cytochrome P-450 Enzyme System; D003513:Cycloheximide; D006899:Mixed Function Oxygenases; D002118:Calcium