title: 1alpha,25-dihydroxyvitamin D3 induced differentiation of cultured human keratinocytes is accompanied by a PKC-independent regulation of AP-1 DNA binding activity.
abstract: 1alpha,25(OH)2D3 and its analogs are potent mediators of keratinocyte differentiation in vitro. The precise mechanism of this action is still unknown. The nuclear transcription factor activator protein 1 seems to play an important role in keratinocyte differentiation. The purpose of this study was to investigate the effect of 1alpha,25(OH)2D3 on activator protein 1 DNA binding activity in cultured human keratinocytes. In a time-course study of human keratinocytes incubated with 1alpha,25(OH)2D3 (10-7-10-11 M) a significant dose-dependent increase in activator protein 1 DNA binding activity as determined by electrophoretic mobility shift assay was seen after 36 h. This increase was followed by a significant dose-dependent decrease in activator protein 1 DNA binding activity after 72 h. When differentiation was induced by raising the calcium concentration in the culture medium from 0.09 to 0.3 mM a similar increase in activator protein 1 DNA binding activity was observed after incubation for 48 h. Pharmacologic down-modulation of the protein kinase C activity with GF 109203X reversed the calcium-induced increase in activator protein 1 DNA binding activity and abolished keratinocyte differentiation as determined by a transglutaminase assay. In contrast, activator protein 1 DNA binding activity and keratinocyte differentiation were not affected when protein kinase C activity was down-modulated in the experiments with 1alpha,25(OH)2D3. The activator protein 1 complex in human keratinocytes consists of dimers of Fra-1, Fra-2, c-Jun, JunD, and c-Fos. Our results demonstrate that 1alpha, 25(OH)2D3- and calcium-induced keratinocyte differentiation are accompanied by changes in activator protein 1 DNA binding activity. Protein kinase C activation appears to be essential for the calcium-dependent induction of keratinocyte differentiation, whereas a protein-kinase-C-independent activation of activator protein 1 DNA binding and keratinocyte differentiation is responsible for the 1alpha,25(OH)2D3-induced effects.
authors.affiliation: Department of Dermatology, Marselisborg Hospital, University of Aarhus, Denmark. clausglotte@mail1.stofanet.dk
authors.forename: C
authors.initials: C
authors.lastname: Johansen
authors.forename: L
authors.initials: L
authors.lastname: Iversen
authors.forename: A
authors.initials: A
authors.lastname: Ryborg
authors.forename: K
authors.initials: K
authors.lastname: Kragballe
mesh_terms: D002117:Calcitriol / Q000737:chemistry / Q000494:pharmacology*; D002118:Calcium / Q000494:pharmacology; D002454:Cell Differentiation / Q000187:drug effects; D004268:DNA-Binding Proteins / Q000378:metabolism; D004789:Enzyme Activation / Q000187:drug effects; D005786:Gene Expression Regulation; D006801:Humans; D015603:Keratinocytes / Q000166:cytology*; D016759:Oncogene Protein p65(gag-jun) / Q000737:chemistry; D016761:Oncogene Proteins v-fos / Q000737:chemistry; D011493:Protein Kinase C / Q000378:metabolism*; D018808:Transcription Factor AP-1 / Q000737:chemistry / Q000235:genetics*
chemical_list: D004268:DNA-Binding Proteins; D016759:Oncogene Protein p65(gag-jun); D016761:Oncogene Proteins v-fos; D018808:Transcription Factor AP-1; D011493:Protein Kinase C; D002117:Calcitriol; D002118:Calcium