Retinoid X Receptor (RXR) Agonist-Induced Activation of Dominant-Negative RXR-Retinoic Acid Receptor α403 Heterodimers Is Developmentally Regulated during Myeloid Differentiation

Abstract

The multiple biologic activities of retinoic acid (RA) are mediated through RAR and retinoid X receptor (RXR) nuclear receptors that interact with specific DNA target sequences as heterodimers (RXR-RAR) or homodimers (RXR-RXR). RA receptor activation appears critical to regulating important aspects of hematopoiesis, since transducing a COOH-terminally truncated RARalpha exhibiting dominant-negative activity (RARalpha403) into normal mouse bone marrow generates hematopoietic growth factor-dependent cell lines frozen at the multipotent progenitor (EML) or committed promyelocyte (MPRO) stages. Nevertheless, relatively high, pharmacological concentrations of RA (1 to 10 microM) overcome these differentiation blocks and induce terminal granulocytic differentiation of the MPRO promyelocytes while potentiating interleukin-3 (IL-3)-induced commitment of EML cells to the granulocyte/monocyte lineage. In the present study, we utilized RXR- and RAR-specific agonists and antagonists to determine how RA overcomes the dominant-negative activity of the truncated RARalpha in these different myeloid developmental stages. Unexpectedly, we observed that an RXR-specific, rather than an RAR-specific, agonist induces terminal granulocytic differentiation of MPRO promyelocytes, and this differentiation is associated with activation of DNA response elements corresponding to RAR-RXR heterodimers rather than RXR-RXR homodimers. This RXR agonist activity is blocked by RAR-specific antagonists, suggesting extensive cross-talk between the partners of the RXR-RARalpha403 heterodimer. In contrast, in the more immature, multipotent EML cells we observed that this RXR-specific agonist is inactive either in potentiating IL-3-mediated commitment of EML cells to the granulocyte lineage or in transactivating RAR-RXR response elements. RA-triggered GALdbd-RARalpha hybrid activity in these cells indicates that the multipotent EML cells harbor substantial nuclear hormone receptor coactivator activity. However, the histone deacetylase (HDAC) inhibitor trichostatin A readily activates an RXR-RAR reporter construct in the multipotent EML cells but not in the committed MPRO promyelocytes, indicating that differences in HDAC-containing repressor complexes in these two closely related but distinct hematopoietic lineages might account for the differential activation of the RXR-RARalpha403 heterodimers that we observed at these different stages of myeloid development.

Retinoic Acid Receptor-Dependent Survival of Olfactory Sensory Neurons in Postnatal and Adult Mice

“…The dnRAR lacks the AF2 ligand-dependent transactivation domain and therefore does not mediate induced transcription in response to retinoic acid. However, RXR agonistdependent activation of RAR␣403-RXR heterodimers cannot be excluded (Damm et al, 1993;Johnson et al, 1999). In situ hybridization analyses of transgenic animals, with a dnRAR-specific probe, showed that OMP promoter-driven dnRAR transcripts were, as expected, specifically expressed in the cell layers containing immature and mature OSNs throughout the olfactory epithelium lining the nasal cavity (Fig.…”

CaMKII regulates retinoic acid receptor transcriptional activity and the differentiation of myeloid leukemia cells

“…Murine PT67 fibroblasts were transfected with the use of calcium phosphate precipitation. All hematopoietic cell lines were transiently transfected by electroporation as previously detailed (45). In the transient transfections the LXSN vector (M28248) served as the expression vector for the WT and site-directed mutagenized CaMKII and RARα coding region cDNAs.…”

“…The luciferase reporter harboring 5 Gal4-binding sites was previously described (45). The complete coding sequence of the human RARα (NM_000964) was amplified by PCR and cloned into the PSG-VP16 vector (46).…”

Retinoid X receptors: X-ploring their (patho)physiological functions

“…185,188,190 In a different model -MPRO promyelocytes -Collins and associates utilized RXR-and RAR-specific agonists and antagonists to determine how RA overcomes the dominant-negative activity of a truncated RARa in myeloid precursor cells. 191 They observed that RXR-specific rather than RAR-specific agonists induce terminal granulocytic differentiation of these cells.…”