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  • Title: Effects of vitamin D3 on keratinocyte proliferation and differentiation in vitro: modulation by ligands for retinoic acid and retinoid X receptors.
    Author: Sørensen S, Sølvsten H, Politi Y, Kragballe K.
    Journal: Skin Pharmacol; 1997; 10(3):144-52. PubMed ID: 9287395.
    Abstract:
    Keratinocytes express receptors for 1,25-dihydroxyvitamin D3 [1,25(OH)2D3], all-trans-retinoic acid (all-trans-RA), 9-cis-retinoic acid (9-cis-RA) and triiodothyronine (T3). The vitamin-D receptor (VDR) can act as a transcription factor by forming homodimers or heterodimers with the retinoic-acid receptor (RAR), the retinoid X receptor (RXR) or the triiodothyronine receptor (TR). This study investigated whether the antiproliferative and prodifferentiating effects of 1,25(OH)2D3 on normal human keratinocyte cultures is modified by all-trans-RA, a ligand for RAR, by CD2809, a ligand for RXR, by 9-cis-RA, a ligand for the RAR and RXR, and T3, a ligand for the TR. Submerged, second-passage normal human keratinocytes were grown to approximately 30% confluency before incubation for 4 days with ligands in keratinocyte growth medium supplemented with 3% charcoal-stripped fetal calf serum and 0.3 mM Ca2+. Proliferation was measured by the dimethylthiazolyl-diphenyl-tetrazolium-bromide assay. Then differentiation was determined in the same culture, performing a cell ELISA for transglutaminase type 1. All-trans-RA, 9-cis-RA and CD2809 had a slight stimulatory effect on proliferation. In combination with 1,25(OH)2D3, all retinoids partially counteracted the antiproliferative effect of 1,25(OH)2D3. The differentiation was dose-dependently inhibited by all-trans-RA, 9-cis-RA and CD2809 alone. In combination with 1,25(OH)2D3, all retinoids reversed the prodifferentiating effect of 1,25(OH)2D3, resulting in a net inhibition of differentiation. T3 had no effect on proliferation of differentiation, either alone or in combination with 1,25(OH)2D3. In conclusion, retinoids with different receptor selectivities had similar effects on keratinocyte proliferation and differentiation. The effects of 1,25(OH)2D3 on proliferation and differentiation were reversed by all retinoids. Therefore ligand-dependent heterodimer formation between the VDR and retinoid receptors may not be important for the combined effects of 1,25(OH)2D3 and retinoids on keratinocyte proliferation and differentiation in vitro.
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