Heterodimer Formation by Retinoid X Receptor:  Regulation by Ligands and by the Receptor's Self-Association Properties

Dong, Diane; Noy, Noa

doi:10.1021/bi980561r

Cited by 52 publications

(48 citation statements)

References 62 publications

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“…Previous studies (e.g. (9,10,21,27)) and the present findings demonstrate that, in addition to regulating the interactions of receptors with transcriptional co-regulators, ligands also control the behavior of their receptors in solution. Hence ligands direct the partitioning of RXR between its various oligomers, and they control the nuclear import of receptors.…”

Section: Discussionsupporting

confidence: 78%

“…Hence apoRXR is predominantly tetrameric, and ligand binding by this receptor yields RXR homodimers (2,4,8). It was also reported that the RXR ligand 9cRA stabilizes RXR homodimers and inhibits the association of RXR with heterodimerization partners such as retinoic acid receptor and VDR (6,9). Ligand binding by either retinoic acid receptor or VDR was found to overcome this inhibition and to stabilize the respective heterodimers even in the presence of 9cRA.…”

mentioning

confidence: 93%

“…Ligand binding by either retinoic acid receptor or VDR was found to overcome this inhibition and to stabilize the respective heterodimers even in the presence of 9cRA. Heterodimerization is thus maximal in the presence of both 9cRA, acting to dissociate RXR tetramers, and the ligand for the partner, which stabilizes the heterodimer (9,10). Whether enhancement of heterodimerization by the ligand for the partner is a general feature of RXR heterodimers remains to be clarified.…”

mentioning

confidence: 99%

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Nuclear Import of the Retinoid X Receptor, the Vitamin D Receptor, and Their Mutual Heterodimer

Yasmin

Williams

et al. 2005

Journal of Biological Chemistry

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The nuclear receptor retinoid X receptor (RXR) can regulate transcription through homotetramers, homodimers, and heterodimers with other nuclear receptors such as the vitamin D receptor (VDR). The mechanisms that underlie the nuclear import of RXR, VDR, and RXR-VDR heterodimers were investigated. We show that RXR and VDR translocate into the nucleus by distinct pathways. RXR strongly bound to importin␤ and was predominantly nuclear in the absence of ligand. Importin binding and nuclear localization of RXR were modestly enhanced by its ligand, 9-cis-retinoic acid. On the other hand, VDR selectively associated with importin␣. Importin association and correspondingly nuclear import of VDR were markedly augmented by 1,25(OH) 2 D 3 . RXR-VDR dimerization inhibited the ability of RXR to bind importin␤ and to mobilize into the nucleus using its own nuclear localization signal. In contrast, VDR recruited RXR-VDR heterodimers to importin␣ and mediated nuclear import of the heterodimers in response to 1,25(OH) 2 D 3 . Hence nuclear import of RXR-VDR heterodimers is mediated preferentially by VDR and is controlled by the VDR ligand. The observations reveal a novel mechanism by which an RXR heterodimerization partner dominates the activity of the heterodimers.The retinoid X receptor (RXR) 3 is a member of the superfamily of nuclear hormone receptors that is activated by the vitamin A metabolite 9-cis-retinoic acid (9cRA). Like other nuclear receptors, RXR is comprised of several distinct functional domains: an amino-terminal domain, involved in ligand-independent basal transcriptional activity; a DNA-binding domain (DBD) containing two "zinc finger" motifs; a flexible hinge region; and a carboxyl-terminal region, termed the ligandbinding domain (LBD). The LBD contains the ligand-binding pocket as well as regions that mediate multiple protein-protein interactions including association with transcriptional co-regulators, formation of dimers, and, in the case of RXR, formation of tetramers. The LBD of nuclear receptors, including RXR, thus coordinates their liganddependent transcriptional activities (1).In the absence of its cognate ligand, RXR forms high affinity homotetramers. These tetramers are transcriptionally silent, but they rapidly dissociate upon ligand binding (2-4). Hence RXR tetramers appear to serve as an inactive storage pool from which active species can be liberated in response to 9cRA. An additional role for the RXR tetramers was recently suggested by the observations that these oligomers act as DNA architectural factors. It was thus demonstrated that binding of RXR tetramers to promoter regions that contain two RXR response elements in tandem results in a dramatic DNA looping, thereby enabling transcriptional regulation by factors placed far upstream from start sites of target genes (5). Hence by modulating DNA geometry, RXR tetramers can regulate gene expression in a manner that is responsive to 9cRA but is independent of the intrinsic transcriptional activity of the receptor (5). Although RXR can activate ...

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Section: Discussionsupporting

confidence: 78%

mentioning

confidence: 93%

mentioning

confidence: 99%

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Nuclear Import of the Retinoid X Receptor, the Vitamin D Receptor, and Their Mutual Heterodimer

Yasmin

Williams

et al. 2005

Journal of Biological Chemistry

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“…The receptor does not form homocomplexes. However, a very tight tetramer of RXR-LBD with a dissociation coefficient K d of a few nM has been reported for an in vitro study (27). The tetramer dissociates in vitro into a monomer͞dimer mixture upon addition of ligand (23).…”

Section: Discussionmentioning

confidence: 99%

Probing protein oligomerization in living cells with fluorescence fluctuation spectroscopy

Chen

Müller

2003

Proc. Natl. Acad. Sci. U.S.A.

203

277

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E very cellular function involves a large number of proteins interacting with one another to fulfill a specific biological task. A characteristic of signaling, metabolic, and other pathways is the reversible association of proteins into complexes as part of a cellular stimulus. The understanding of biological cells requires understanding the intricate and entangled interactions between proteins. Detecting and measuring protein association of cellular proteins is an important first step for ultimately piecing together the inner workings of the cellular machinery. However, we lack spectroscopic tools for directly determining protein interactions in cells. Here, we describe a technique with the capability to detect protein oligomerization in living cells based on fluorescence fluctuation spectroscopy (FFS).FFS is a very sensitive technique that probes the dynamics and concentration of fluorescent molecules in optical observation volumes of Ϸ1 fl. Each fluorophore passing through the observation volume is excited by laser light and emits fluorescence, which is registered by a photo detector and produces a small signal fluctuation. Statistical analysis of the signal fluctuations recovers information about fluorophores. Calculation of correlation functions is the most widely used technique and is also known as fluorescence correlation spectroscopy (FCS) (1). Here we will focus on two other ways of analyzing fluctuations, photon counting histogram (PCH) (2) and moment analysis (3). Both techniques determine the molecular brightness and the occupation number in the observation volume. Another brightness technique (fluorescence intensity distribution analysis, FIDA) that is similar to PCH has also been described in the literature (4).Molecular brightness is defined as the average detected photon count rate for a fluorophore. It depends on instrumental parameters, such as the excitation wavelength and the quantum yield of the detector. If instrumental parameters are kept constant, molecular brightness characterizes a photophysical property of the fluorescent molecule. We use molecular brightness to monitor protein association. If a fluorescently labeled protein diffuses through the observation volume, it will produce a burst of detected photons. The average photon count rate of these bursts determines the molecular brightness of the labeled protein. If such a protein associates to form a homodimer, the new complex will carry two fluorescent labels. The complex will produce, on average, twice as many photons than is the case for the monomeric protein, because two independently fluorescing molecules are participating. Consequently, the molecular brightness of the dimer is twice that of the monomer (5). Fluorescent labeling of proteins in cells is performed by constructing a fusion protein tagged with a GFP. Expression of This paper was submitted directly (Track II) to the PNAS office.

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“…The following methods were used: 1) chemical crosslinking (13), 2) electrophoresis under nondenaturing conditions, 3) fluorescence anisotropy titrations (24,25), 4) electrophoretic mobility-shift assays, intended to examine whether cognate DNA may stabilize the complex (25). We could not detect complex formation using any of these methods.…”

Section: Crabp-i and Crabp-ii Deliver Ra To Rar By Differentmentioning

confidence: 99%

Distinct Roles for Cellular Retinoic Acid-binding Proteins I and II in Regulating Signaling by Retinoic Acid

Dong

Ruuska

Levinthal

et al. 1999

Journal of Biological Chemistry

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316

275

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Heterodimer Formation by Retinoid X Receptor: Regulation by Ligands and by the Receptor's Self-Association Properties

Cited by 52 publications

References 62 publications

Nuclear Import of the Retinoid X Receptor, the Vitamin D Receptor, and Their Mutual Heterodimer

Nuclear Import of the Retinoid X Receptor, the Vitamin D Receptor, and Their Mutual Heterodimer

Probing protein oligomerization in living cells with fluorescence fluctuation spectroscopy

Distinct Roles for Cellular Retinoic Acid-binding Proteins I and II in Regulating Signaling by Retinoic Acid

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