Distinct retinoid X receptor activation function-2 residues mediate transactivation in homodimeric and vitamin D receptor heterodimeric contexts

P. D. Thompson, L. S. Remus, J. C. Hsieh, P. W. Jurutka, G. K. Whitfield, M. A. Galligan, C. Encinas Dominguez, C. A. Haussler, M. R. Haussler

Research output: Contribution to journalArticle

54 Scopus citations

Abstract

The vitamin D receptor (VDR) stimulates transcription as a 1,25-dihydroxyvitamin D3 (1,25(OH)2D3)-activated heterodimer with retinoid X receptor (RXR). RXR also forms homodimers to mediate 9-cis retinoic acid (9-cis RA)-induced gene expression. Both receptors possess a C-terminal hormone-dependent activation function-2 (AF-2), a highly conserved region that binds coactivators to transduce the transcriptional signal. By replacing single amino acids within the AF-2 of human RXRα (hRXRa) or mouse RXRβ (mRXRβ), the contribution of these residues to transactivation by the RXR-VDR heterodimer and the RXR-RXR homodimer was evaluated. In 9-cis RA-responsive homodimers, the second and fourth positions of the AF-2 (leucine and glutamate respectively) are essential. However, in the context of an RXR-VDR heterodimer activated by 1,25(OH)2D3, alteration of these two RXR residues has little effect. Instead, AF-2 residues located towards the C-terminus, such as the penultimate position (L455 in hRXRα or L441 in mRXRβ), are crucial for RXR-VDR heterodimers. Indeed, L455A mutant RXR exerts a dominant negative effect on RXR-VDR transcriptional responsiveness to 1,25(OH)2D3. Further experiments with a mutant hRXRα (F313A) which elicits 9-cis RA-independent transactivation as a homodimer demonstrate that, when heterodimerized with VDR, this RXR mutant is incapable of activating the RXR-VDR heterocomplex in the absence of the VDR ligand. Taken together, these results indicate that RXR is a subordinate, yet essential transcriptional partner in RXR-VDR-mediated activation of gene expression. Furthermore, a functional switch in RXR AF-2 signaling occurs between RXR residues in the homodimeric versus the heterodimeric states, likely reflecting different interactions between subregions of the AF-2 and coactivator(s).

Original languageEnglish (US)
Pages (from-to)211-227
Number of pages17
JournalJournal of Molecular Endocrinology
Volume27
Issue number2
DOIs
StatePublished - Oct 25 2001

ASJC Scopus subject areas

  • Molecular Biology
  • Endocrinology

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