1α,25-dihydroxyvitamin D3 transrepresses retinoic acid transcriptional activity via vitamin D receptor in myeloid cells

Granulocytes and monocytes originate from a common committed progenitor cell. Commitment to either granulocytic or monocytic lineage is triggered by specific extracellular signals involving cytokines or nuclear receptor ligands (all-trans-retinoic acid (RA) and 1alpha,25-dihydroxyvitamin D-3). Here we show that the stimulatory effect of 1alpha,25-dihydroxyvitamin D-3 on the production of monocytic colonies (CFU-M) is accompanied by a repression of granulocytic colony (CFU-G) production. We further demonstrate that in bipotent HL-60 myeloid cells as in purified human CD34+ myeloid progenitor cells, the 1alpha,25-dihydroxyvitamin D-3- induced monocytic differentiation is concomitant with a direct inhibition of the RA-transcriptional activity. Indeed, a transrepression of the RARbeta RA-target gene promoter via formation of a nuclear complex involving VDR was identified in vitro and in vivo. The fact that binding of RXR-RAR on DR3 is not observed suggests that contrary to RA-induced granulocytic differentiation, 1alpha,25-dihydroxyvitamin D-3-mediated monocytic differentiation requires positive and negative transcriptional controls both likely mediated by the RXR-VDR heterodimer. These novel findings implicate that 1alpha,25-dihydroxyvitamin D-3 exerts a dominant negative effect on the RA-dependent granulocytic commitment of human bone marrow cells via repression of the RA-target gene promoters. Hence, the transcriptional response to RA and 1alpha,25-dihydroxyvitamin D-3 in myeloid cells depends on a complex combinatory pattern of interaction among different nuclear receptors with DNA.