1 alpha,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 1 alpha,25-dihydroxyvitamin D(3)). Here we show that the stimulatory effect of 1 alpha,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 1 alpha,25-dihydroxyvitamin D(3)-induced monocytic differentiation is concomitant with a direct inhibition of the RA-transcriptional activity. Indeed, a transrepression of the RAR beta 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, 1 alpha,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 1 alpha,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 1 alpha,25-dihydroxyvitamin D(3) in myeloid cells depends on a complex combinatory pattern of interaction among different nuclear receptors with DNA.