It looks like the "phantom effect" of RXR ligands applies to PPARs also (an earlier publication indicated that such an effect could influence RARs):
Mol Cell Biol 1998 Jun;18(6):3483-3494
Transactivation by retinoid X receptor-peroxisome proliferator-activated
receptor gamma (PPARgamma) heterodimers: intermolecular synergy
requires only the PPARgamma hormone-dependent activation function.
Schulman IG, Shao G, Heyman RA
Department of Retinoid Research, Ligand Pharmaceuticals, San Diego, California 92121, USA.
[Medline record in process]
The ability of DNA sequence-specific transcription factors to synergistically activate transcription is a common property of genes
transcribed by RNA polymerase II. The present work characterizes a unique form of intermolecular transcriptional synergy
between two members of the nuclear hormone receptor superfamily. Heterodimers formed between peroxisome
proliferator-activated receptor gamma (PPARgamma), an adipocyte-enriched member of the superfamily required for
adipogenesis, and retinoid X receptors (RXRs) can activate transcription in response to ligands specific for either subunit of the
dimer. Simultaneous treatment with ligands specific for both PPARgamma and RXR has a synergistic effect on the transactivation
of reporter genes and on adipocyte differentiation in cultured cells. Mutation of the PPARgamma hormone-dependent activation
domain (named tauc or AF-2) inhibits the ability of RXR-PPARgamma heterodimers to respond to ligands specific for either
subunit. In contrast, the ability of RXR- and PPARgamma-specific ligands to synergize does not require the hormone-dependent
activation domain of RXR. The results of in vitro and in vivo experiments indicate that binding of ligands to RXR alters the
conformation of the dimerization partner, PPARgamma, and modulates the activity of the heterodimer in a manner independent of
the RXR hormone-dependent activation domain.
PMID: 9584188, UI: 98252935
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