EGF Receptor expression and growth of psoriatic and normal human keratinocytes are modulated by 1.25 (OH)2-vitamin D3 ex vivo

Calcitriol or 1,25 (OH)₂-vitamin D₃ is used in the treatment of psoriasis as an inhibitor of cell proliferation. We studied the action of calcitriol ex vivo on the growth of psoriatic and normal human keratinocytes, and on the expression of the EGF receptor. Third passaged normal and psoriatic keratinocytes were seeded (10⁴/cm²) in 24-well dishes in serum-free medium (MCDB supplemented with amino acids, with either 0.1 or 1.1 mM of calcium) and 10⁻⁹ M calcitriol. When subconfluence was reached, cell counts and¹²⁵I-EGF binding studies were performed. Cell counts showed at least a 50% decrease in growth under all conditions studied (normal or psoriatic keratinocytes; 0.1 or 1.1 mM calcium) when calcitriol was added.¹²⁵I-EGF binding studies showed a decrease in total receptor numbers in the presence of calcitriol with acceleration of binding at low concentrations of¹²⁵I-EGF. Scatchard plot analysis showed only one type of high affinity receptor. Receptor sites were decreased (30% to 40% of controls) in the presence of calcitriol together with a decrease in the dissociation constant. In conclusion, at almost physiological concentrations ex vivo, calcitriol strongly decreased normal and psoriatic keratinocyte growth. This potent antiproliferative effect could in part be explained by the capacity of calcitriol to downregulate EGF receptor expression. Supported by grants of the Conseil Régional de la Région Aquitaine, and of the Université de Bordeaux II, to AT