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Molecular and Cellular Biology, January 2000, p. 187-195, Vol. 20, No. 1
Department of Molecular and Cellular Biology,
Baylor College of Medicine, Houston, Texas
77030,1 and Department of Medicine, Section
of Molecular Genetics, Cardiovascular Institute, Boston University
School of Medicine, Center for Advanced Biomedical Research, Boston,
Massachusetts 021182
Received 26 July 1999/Returned for modification 25 August
1999/Accepted 27 September 1999
The orphan nuclear hormone receptor SHP interacts with a number of
other nuclear hormone receptors and inhibits their transcriptional activity. Several mechanisms have been suggested to account for this
inhibition. Here we show that SHP inhibits transactivation by the
orphan receptor hepatocyte nuclear factor 4 (HNF-4) and the retinoid X
receptor (RXR) by at least two mechanisms. SHP interacts with the same
HNF-4 surface recognized by transcriptional coactivators and competes
with them for binding in vivo. The minimal SHP sequences previously
found to be required for interaction with other receptors are
sufficient for interaction with HNF-4, although deletion results
indicate that additional C-terminal sequences are necessary for full
binding and coactivator competition. These additional sequences include
those associated with direct transcriptional repressor activity of SHP.
SHP also competes with coactivators for binding to ligand-activated
RXR, and based on the ligand-dependent interaction with other nuclear
receptors, it is likely that coactivator competition is a general
feature of SHP-mediated repression. The minimal receptor interaction
domain of SHP is sufficient for full interaction with RXR, as
previously described. This domain is also sufficient for full
coactivator competition. Functionally, however, full inhibition of RXR
transactivation requires the presence of the C-terminal repressor
domain, with only weak inhibition associated with this receptor
interaction domain. Overall, these results suggest that SHP represses
nuclear hormone receptor-mediated transactivation via two separate
steps: first by competition with coactivators and then by direct
effects of its transcriptional repressor function.
0270-7306/0/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.
The Orphan Nuclear Receptor SHP Inhibits Hepatocyte Nuclear
Factor 4 and Retinoid X Receptor Transactivation: Two Mechanisms
for Repression
*
Corresponding author. Mailing address: Department of
Molecular and Cellular Biology, Baylor College of Medicine, One Baylor Plaza, Houston, TX 77030. Phone: (713) 798-3313. Fax: (713) 798-3017. E-mail: moore{at}bcm.tmc.edu.
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