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Molecular and Cellular Biology, May 1999, p. 3372-3382, Vol. 19, No. 5
Division of Hospital Dentistry, University of
Washington, Seattle, Washington 981951;
Retinoid Research, Departments of
Biology2 and
Chemistry,3 Allergan Pharmaceuticals,
Irvine, California 92715; Department of Retinoid Research,
Ligand Pharmaceuticals, San Diego, California
921214; and Division of Molecular
Medicine, Fred Hutchinson Cancer Research Center, Seattle,
Washington 981095
Received 31 August 1998/Returned for modification 20 November
1998/Accepted 25 January 1999
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 RAR
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Copyright © 1999, American Society for Microbiology. All rights reserved.
Retinoid X Receptor (RXR) Agonist-Induced
Activation of Dominant-Negative RXR-Retinoic Acid Receptor
403
Heterodimers Is Developmentally Regulated during Myeloid
Differentiation
exhibiting dominant-negative activity
(RAR
403) 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 µM) 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 RAR
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-RAR
403 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-RAR
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-RAR
403 heterodimers that we observed at these
different stages of myeloid development.
*
Corresponding author. Mailing address: Division of
Molecular Medicine, Fred Hutchinson Cancer Research Center, 1100 Fairview Ave., North, Seattle, WA 98109. Phone: (206) 667-4389. Fax:
(206) 667-6523. E-mail: scollins{at}fhcrc.org.
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