Regulation of AML2/CBFA3 in hematopoietic cells through the retinoic acid receptor α-dependent signaling pathway

AML2 is a member of the acute myelogenous leukemia, AML family of transcription factors. The biologic functions of AML1 and AML3 have been well characterized; however, the functional role of AML2 remains unknown. In this study, we found that AML2 protein expressed predominantly in cells of hematopoietic origin is a nuclear serine phosphoprotein associated with the nuclear matrix, and its expression is not cell cycle-related. In HL-60 cells AML2 expression can be induced by all three natural retinoids, all-trans- retinoic acid (RA), 13-cis-RA, and 9-cis-RA in a dose-dependent manner. A synthetic retinoic acid derivative, 4HPR, which neither activates RA receptor (RAR) α nor retinoic X receptor was unable to induce the expression of AML2. A RAR-selective activator, TTNPB, induced AML2 expression similar to RA. Our study further showed that AGN193109, a potent RARα antagonist, suppressed AML2 expression induced by RA and that a retinoic X receptor pan agonist AGN194204 had no effect on its expression. Taken together, these studies conclusively demonstrated that the expression of ML2 in HL-60 cells is regulated through the RARα-specific signaling pathway. Our study further showed that after all-trans-retinoic acid priming, AML2 expression could be augmented by vitamin D₃. Based on these studies we hypothesize that AML2 expression is normally regulated by retinoid/vitamin D nuclear receptors mainly through the RARα-dependent signaling pathway and that it may play a role in hematopoietic cell differentiation.