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The quaternary architecture of RAR?-RXR? heterodimer facilitates domain-domain signal transmission.

ABSTRACT: Assessing the physical connections and allosteric communications in multi-domain nuclear receptor (NR) polypeptides has remained challenging, with few crystal structures available to show their overall structural organizations. Here we report the quaternary architecture of multi-domain retinoic acid receptor ?-retinoic X receptor ? (RAR?-RXR?) heterodimer bound to DNA, ligands and coactivator peptides, examined through crystallographic, hydrogen-deuterium exchange mass spectrometry, mutagenesis and functional studies. The RAR? ligand-binding domain (LBD) and DNA-binding domain (DBD) are physically connected to foster allosteric signal transmission between them. Direct comparisons among all the multi-domain NRs studied crystallographically to date show significant variations within their quaternary architectures, rather than a common architecture adhering to strict rules. RXR remains flexible and adaptive by maintaining loosely organized domains, while its heterodimerization partners use a surface patch on their LBDs to form domain-domain interactions with DBDs.Nuclear receptors (NR) are multidomain proteins, which makes their crystallization challenging. Here the authors present the crystal structure of the retinoic acid receptor ?-retinoic X receptor ? (RAR?-RXR?) heterodimer bound to DNA, ligands and coactivator peptides, which shows that NR quaternary architectures are variable.

SUBMITTER: Chandra V

PROVIDER: S-EPMC5636793 | biostudies-literature | 2017 Oct

REPOSITORIES: biostudies-literature

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The quaternary architecture of RARβ-RXRα heterodimer facilitates domain-domain signal transmission.

Chandra Vikas V Wu Dalei D Li Sheng S Potluri Nalini N Kim Youngchang Y Rastinejad Fraydoon F

Nature communications 20171011 1

Assessing the physical connections and allosteric communications in multi-domain nuclear receptor (NR) polypeptides has remained challenging, with few crystal structures available to show their overall structural organizations. Here we report the quaternary architecture of multi-domain retinoic acid receptor β-retinoic X receptor α (RARβ-RXRα) heterodimer bound to DNA, ligands and coactivator peptides, examined through crystallographic, hydrogen-deuterium exchange mass spectrometry, mutagenesis ...[more]

PMID: 29021580

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Project description:Differentiation of embryonic and adult myogenic progenitors undergoes a complex series of cell rearrangements and specification events which are controlled by distinct gene regulatory networks. Delineation of the molecular mechanisms that regulate skeletal muscle specification and formation should be important for understanding congenital myopathies and muscular degenerative diseases. Retinoic acid (RA) signaling plays an important role in development. However, the role of RA signaling in adult myogenic progenitors is poorly understood. Here, we investigate the role of RA signaling in regulating myogenic differentiation of myoblastic progenitor cells. Using the mouse myoblast progenitor C2C12 line as a model, we have found that the endogenous expression of most RAR and RXR isotypes is readily detected. While the nuclear receptor co-repressors are highly expressed, two of the three nuclear receptor co-activators and the enzymes involved in RA synthesis are expressed at low level or undetectable, suggesting that the RA signaling pathway may be repressed in myogenic progenitors. Using the alpha-myosin heavy chain promoter-driven reporter (MyHC-GLuc), we have demonstrated that either ATRA or 9CRA is able to effectively induce myogenic differentiation, which can be synergistically enhanced when both ATRA and 9CRA are used. Upon ATRA and 9CRA treatment of C2C12 cells the expression of late myogenic markers significantly increases. We have further shown that adenovirus-mediated exogenous expression of RARalpha and/or RXRalpha is able to effectively induce myogenic differentiation in a ligand-independent fashion. Morphologically, ATRA- and 9CRA-treated C2C12 cells exhibit elongated cell body and become multi-nucleated myoblasts, and even form myoblast fusion. Ultrastructural analysis under transmission electron microscope reveals that RA-treated myogenic progenitor cells exhibit an abundant presence of muscle fibers. Therefore, our results strongly suggest that RA signaling may play an important role in regulating myogenic differentiation.

Project description:Macrophage foam cells store excess cholesterol as cholesteryl esters, which need to be hydrolyzed for cholesterol efflux. We recently reported that silencing expression of carboxylesterase 1 (CES1) in human THP-1 macrophages [CES1KD (THP-1 cells with CES1 expression knocked down) macrophages] reduced cholesterol uptake and decreased expression of CD36 and scavenger receptor-A in cells loaded with acetylated low-density lipoprotein (acLDL). Here, we report that CES1KD macrophages exhibit reduced transcription of cytochrome P45027A1 (CYP27A1) in nonloaded and acLDL-loaded cells. Moreover, levels of CYP27A1 protein and its enzymatic product, 27-hydroxycholesterol, were markedly reduced in CES1KD macrophages. Transcription of LXR? (liver X receptor ?) and ABCA1 (ATP-binding cassette transporter A1) was also decreased in acLDL-loaded CES1KD macrophages, suggesting reduced signaling through PPAR?-CYP27A1-LXR?. Consistent with this, treatment of CES1KD macrophages with agonists for PPAR?, RAR, and/or RAR/RXR partially restored transcription of CYP27A1 and LXR?, and repaired cholesterol influx. Conversely, treatment of control macrophages with antagonists for PPAR? and/or RXR decreased transcription of CYP27A1 and LXR? Pharmacologic inhibition of CES1 in both wild-type THP-1 cells and primary human macrophages also decreased CYP27A1 transcription. CES1 silencing did not affect transcript levels of PPAR? and RXR in acLDL-loaded macrophages, whereas it did reduce the catabolism of the endocannabinoid 2-arachidonoylglycerol. Finally, the gene expression profile of CES1KD macrophages was similar to that of PPAR? knockdown cells following acLDL exposures, further suggesting a mechanistic link between CES1 and PPAR?. These results are consistent with a model in which abrogation of CES1 function attenuates the CYP27A1-LXR?-ABCA1 signaling axis by depleting endogenous ligands for the nuclear receptors PPAR?, RAR, and/or RXR that regulate cholesterol homeostasis.

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The quaternary architecture of RAR?-RXR? heterodimer facilitates domain-domain signal transmission.

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The quaternary architecture of RARβ-RXRα heterodimer facilitates domain-domain signal transmission.

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