EXPRESSION OF VITAMIN-D-RECEPTOR (VDR) IN HL-60 CELLS IS DIFFERENTIALLY REGULATED DURING THE PROCESS OF DIFFERENTIATION-INDUCED BY PHORBOL ESTER, RETINOIC ACID OR INTERFERON-GAMMA

The effects of three inducers of differentiation, phorbol myristate ac etate (PMA), retinoic acid (RA) and interferon-gamma (IFN-gamma), on t he temporal regulation of vitamin D receptor (VDR) expression in HL-60 cells were analyzed by Northern blotting and immunofluorescence assay s. VDR, at the protein level, expressed by 81% of uninduced cells, was reduced to 57% after 48 h of PMA or 96 h of RA treatment, preceded by growth inhibition and cell differentiation, evaluated by CD11b expres sion. Sorted CD11b positive cells in G0/G1 phase exhibited 53% the VDR content of CD11b negative cells (distributed throughout the cell cycl e). PMA also induced an increase in PKC beta and PKC alpha mRNA and pr otein. Simultaneous exposure to PMA and sphingosine blocked stimulatio n of CD11b and PKC expression without affecting growth arrest and VDR down regulation. Similar effects were observed during sphingosine trea tment. In IFN-gamma differentiated cells, the proportion of cells in G 0/G1 phase was unchanged and VDR protein was unaltered as compared to uninduced cells. Control cells in G0/G1 expressed less VDR than cells in S and G2/M phases (74% and 59% respectively). All results suggest t hat in HL-60 cells, reduction of VDR expression is related to growth i nhibition rather than to the differentiation process. (C) 1998 Elsevie r Science Ltd. All rights reserved.