Human Leukemic (HMC-1) Mast Cells Are Responsive to 1α,25-Dihydroxyvitamin D3: Selective Promotion of ICAM-3 Expression and Constitutive Presence of Vitamin D3 Receptor

Abstract

Expression levels of adhesion molecules on HMC-1 mast cells were examined prior to and following administration of 1α,25-dihydroxyvitamin D3 [1,25(OH)2D3]. While most receptors (including ICAM-1) remained unchanged by the treatment, solely ICAM-3 expression was promoted in a dose- and time-dependent fashion, peaking at 50 nM of 1,25(OH)2D3 and 72 h, illustrating that like other myeloid cells, human mast cells are 1,25(OH)2D3 responsive, yet in a highly selective manner. Flow cytometric results were confirmed by ELISA, by semiquantitative RT-PCR, and functionally by showing enhanced anti-ICAM-3 mediated homotypic aggregation of 1,25(OH)2D3 pretreated cells. Since cellular responsiveness is conferred by the vitamin D3 receptor (VDR), we examined human mast cells for its expression. VDR was constitutively present in both HMC-1 and skin mast cells by RT-PCR technique and in nuclear extracts of HMC-1 cells by Western blot analysis. Our data thus suggest that human mast cells are direct targets of 1,25(OH)2D3 action.