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- γ

Abstract

The effects of three inducers of differentiation, phorbol myristate acetate (PMA), retinoic acid (RA) and interferon- γ (IFN- γ), on the temporal regulation of vitamin D receptor (VDR) expression in HL-60 cells were analyzed by Northern blotting and immunofluorescence assays. 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 expression. Sorted CD11b positive cells in G0/G1 phase exhibited 53% the VDR content of CD11b negative cells (distributed throughout the cell cycle). PMA also induced an increase in PKC β and PKC α mRNA and protein. Simultaneous exposure to PMA and sphingosine blocked stimulation of CD11b and PKC expression without affecting growth arrest and VDR down regulation. Similar effects were observed during sphingosine treatment. In IFN- γ differentiated cells, the proportion of cells in G0/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 that in HL-60 cells, reduction of VDR expression is related to growth inhibition rather than to the differentiation process.