Expression of multiple cytochrome P450 enzymes and multidrug resistance-associated transport proteins in human skin keratinocytes

Cytochrome P450 enzymes metabolize various endogenous and exogenous small m olecular weight compounds. Transport-associated proteins, such as P-glycopr otein, multidrug resistance-associated protein and lung resistance protein are overexpressed in drug-resistant cell lines, as well as in human tumors from various histologic origins, including malignant melanoma, Little is kn own about the expression and function of cytochrome enzymes and multidrug r esistance-associated transport proteins in human skin; therefore, the aim o f this study was to analyze the expression pattern of cytochrome enzymes an d multidrug resistance-associated transport proteins in proliferating human epidermal keratinocytes under constitutive conditions and after induction with various inducers. Reverse transcription-polymerase chain reaction reve aled constitutive expression of cytochromes 1A1, 1B1, 2B6, 2E1, and 3A5 in keratinocytes and showed expression of cytochrome 3A4 after incubation with dexamethasone, The expression of cytochrome 1A1 was enhanced on the mRNA l evel after induction with benzanthracene. Reverse transcription-polymerase chain reaction analysis of the multidrug resistance-associated transport pr oteins revealed constitutive expression of multidrug resistance-associated proteins 1 and 3-6, and lung resistance protein in human epithelial keratin ocytes and was negative for multidrug resistance 1 and 2, Expression of 1 w as seen after induction with dexamethasone, Reverse transcription-polymeras e chain reaction results were confirmed by immunoblots which showed express ion of cytochromes 1A1, 2B6, 2E1, and 3A, multidrug resistance-associated p roteins 1, 3, and 5 as well as multidrug resistance 1 after induction with dexamethasone. Immunohistology showed positive immunofluorescence in skin s pecimens for cytochromes 1A1, 2B6, 2E1, and 3A and multidrug resistance-ass ociated protein 1 and multidrug resistance 1, Constitutive activity of cyto chrome 1A1, 2B, 2E1, and 3A enzymes was measured by catalytic assays, These results show that keratinocytes of the human skin express various transpor t-associated enzymes and detoxifying metabolic enzymes. Previous studies ha ve revealed that cytochrome enzymes and transport-associated proteins play complementary parts in drug disposition by biotransformation (phase I) and anti-transport (phase III) and act synergistically as a drug bioavailabilit y barrier.