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"RORA" redirects here. For other uses, see Rora (disambiguation).

RAR-related orphan receptor alpha (RORα), also known as NR1F1 (nuclear receptor subfamily 1, group F, member 1) is a nuclear receptor that in humans is encoded by the RORA gene.[1]

Protein

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Structure

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The protein encoded by this gene is a member of the NR1 subfamily of nuclear hormone receptors. [2] In humans, 4 isoforms of RORα have been identified, which are generated via alternative splicing and promoter usage, and exhibit differential tissue-specific expression. The protein structure of RORα consists of four canonical functional groups: an N-terminal (A/B) domain, a DNA-binding domain containing two zinc fingers, a hinge domain, and a C-terminal ligand-binding domain. Within the ROR family, the DNA-binding domain is highly conserved, and the ligand-binding domain is only moderately conserved.[3] Different isoforms of RORα have different binding specificities and strengths of transcriptional activity.[1]

Mechanisms

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Specific association with ROR elements (RORE) in regulatory regions is necessary for RORα’s function as a transcriptional activator.[4] RORα achieves this by specific binding to a consensus core motif in RORE, RGGTCA. This interaction is possible through the association of RORα’s first zinc finger with the core motif in the major groove, the P-box, and the association of its C-terminal extension with the AT-rich region in the 5’ region of RORE.[2]

Homology

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RORα, RORβ, and RORγ are all transcriptional activators recognizing ROR-response elements.[5] ROR-alpha is expressed in a variety of cell types and is involved in regulating several aspects of development, inflammatory responses, and lymphocyte development.[6] The RORα isoforms (RORα1 through RORα3) arise via alternative RNA processing, with RORα2 and RORα3 sharing an amino-terminal region different from RORα1.[7] In contrast to RORα, RORβ is expressed in Central Nervous System (CNS) tissues involved in processing sensory information and in generating circadian rhythms while RORγ is critical in lymph node organogenesis and thymopoeisis.[6]

The DNA-binding domains of the DHR3 orphan receptor in Drosophila shows especially close homology within amino and carboxy regions adjacent to the second zinc finger region in RORα, suggesting that this group of residues is important for the proteins' functionalities.[1]

PDP1 and VRI in Drosophila regulate circadian rhythm's by competing for the same binding site, the VP box, similarly to how ROR and REV-ERB competitively bind to RRE. [8] PDP1 and VRI constitute a feedback loop and are functional homologs of ROR and REV-ERB in mammals. [8]

Direct orthologs of this gene have been identified in mice and humans.

Human cytochrome c pseudogene HC2 and RORα share overlapping genomic organization with the HC2 pseudogene located within the RORα2 transcription unit. The nucleotide and deduced amino acid sequences of cytochrome c-processed pseudogene are on the sense strand while those of the RORα2 amino-terminal exon are on the antisense strand.[1]

Discovery

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The first three human isoforms of RORα were initially cloned and characterized as nuclear receptors in 1994 by Giguere and colleagues, when their structure and function were first studied.[9]

In the early 2000s, various studies demonstrated that RORα displays rhythmic patterns of expression in a circadian cycle in the liver, kidney, retina, and lung[3]. Of interest, it was around this time that RORα abundance was found to be circadian in the mammalian Suprachiasmatic nucleus,[10]. RORα is necessary for normal circadian rhythms in mice,[2] demonstrating its importance in chronobiology.

Role in circadian rhythms

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The core mammalian circadian clock is a negative feedback loop which consists of Per1/Per2, Cry1/Cry2, Bmal1, and Clock.[10] This feedback loop is stabilized through another loop involving the transcriptional regulation of Bmal1.[8] Transactivation of Bmal1 is regulated through the upstream ROR/REV-ERB Response Element (RRE) in the Bmal1 promoter, to which RORα and REV-ERBα bind.[8] This stabilizing regulatory loop itself is induced by the Bmal1/Clock heterodimer, which induces transcription of RORα and REV-ERBα.[10] RORα, which activates transcription of Bmal1, and REV-ERBα, which represses transcription of Bmal1, compete to bind to the RRE.[8] This feedback loop regulating the expression of Bmal1 is thought to stabilize the core clock mechanism, helping to buffer it against changes in the environment[8].

Interactions

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  • DNA: RORα binds to the P-box of the RORE.[2]
  • Co-activators:
    • SRC-1, CBP, p300, TRIP-l, TRIP-230, transcription intermediary protein-1 (TIF-1), peroxisome proliferator-binding protein (PBP), and GRIP-1 physically interact with RORα.[3]
      • LXXLL motif: ROR interacts with SRC-1, GRIP-l, CBP, and p300 via the LXXLL (L=Leucine, X=any amino acid) motifs on these proteins.[3]
  • Ubiquitination: RORα is targeted for the proteasome by ubiquitination. A co-repressor, Hairless, stabilizes RORα by protecting it from this process, which also represses RORα.[11]
  • Sumoylation: UBE21/UBC9: Ubiquitin-conjugating enzyme I interacts with RORs, but its effect is not yet known.[2]
  • Phosphorylation:
  • ATXN1: ATXN1 and RORα form part of a protein complex in Purkinje cells.[2]
  • FOXP3: FOXP3 directly represses the transcriptional activity of RORs.[2]
  • NME1: ROR has been shown to specifically interact with NME1.[13]
  • NM23-2: NM23-2 is a nucleoside diphosphate kinase involved in organogenesis and differentiation.[14]
  • NM23-1: NM23-1 is the product of a tumor metastasis suppressor candidate gene. [14]

Clinical Significance

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Because RORα and REV-ERBα are nuclear receptors that share the same target genes and are involved in processes that regulate metabolism, development, immunity, and circadian rhythm, they show potential as drug targets. Synthetic ligands have a variety of therapeutic uses, and can be used to treat diseases such as diabetes, atherosclerosis, autoimmunity, and cancer. T0901317 and SR1001, two synthetic ligands, have been found to be RORα and RORγ inverse agonists that suppress reporter activity and have been shown to delay onset and clinical severity of Multiple Sclerosis and other T17 cell-mediated autoimmune diseases. SR1078 has been discovered as a RORα and RORγ agonist that increases the expression of G6PC and FGF21, yielding the therapeutic potential to treat obesity and diabetes as well as cancer of the breast, ovaries, and prostate. SR3335 has also been discovered as a RORα inverse agonist.[9]

See also

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References

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  1. ^ a b c d Giguère V, Tini M, Flock G, Ong E, Evans RM, Otulakowski G (Mar 1994). "Isoform-specific amino-terminal domains dictate DNA-binding properties of ROR alpha, a novel family of orphan hormone nuclear receptors". Genes & Development. 8 (5): 538–553. doi:10.1101/gad.8.5.538. PMID 7926749.
  2. ^ a b c d e Jetten AM, Kurebayashi S, Ueda E (2001). "The ROR nuclear orphan receptor subfamily: critical regulators of multiple biological processes". Progress in Nucleic Acid Research and Molecular Biology. 69: 205–247. doi:10.1016/S0079-6603(01)69048-2. ISBN 9780125400695. PMID 11550795.
  3. ^ Laitinen S, Staels B (2003). "Potential roles of ROR-alpha in cardiovascular endocrinology". Nuclear Receptor Signaling. 1: nrs.01011. doi:10.1621/nrs.01011. PMC 1402228. PMID 16604183.
  4. ^ Zhao X, Cho H, Yu RT, Atkins AR, Downes M, Evans RM (May 2014). "Nuclear receptors rock around the clock". EMBO Reports. 15 (5): 518–528. doi:10.1002/embr.201338271. PMC 4210094. PMID 24737872.
  5. ^ a b Du J, Huang C, Zhou B, Ziegler SF (Apr 2008). "Isoform-specific inhibition of ROR alpha-mediated transcriptional activation by human FOXP3". Journal of Immunology. 180 (7): 4785–4792. doi:10.4049/jimmunol.180.7.4785. PMID 18354202. S2CID 85729490.
  6. ^ Cite error: The named reference Isoform-specific amino-terminal domains dictate DNA-binding properties of RORα, a novel family of orphan hormone nuclear receptors was invoked but never defined (see the help page).
  7. ^ a b c d e f Emery P, Reppert SM (Aug 2004). "A rhythmic Ror". Neuron. 43 (4): 443–446. doi:10.1016/j.neuron.2004.08.009. PMID 15312644. S2CID 1565916.
  8. ^ a b Kojetin DJ, Burris TP (Mar 2014). "REV-ERB and ROR nuclear receptors as drug targets". Nature Reviews. Drug Discovery. 13 (3): 197–216. doi:10.1038/nrd4100. PMC 4865262. PMID 24577401.
  9. ^ a b c Ko CH, Takahashi JS (Oct 2006). "Molecular components of the mammalian circadian clock". Human Molecular Genetics. 15 Spec No 2 (2): R271–R277. doi:10.1093/hmg/ddl207. PMID 16987893.
  10. ^ Xiong G, Wang C, Evers BM, Zhou BP, Xu R (Apr 2012). "RORα suppresses breast tumor invasion by inducing SEMA3F expression". Cancer Research. 72 (7): 1728–1739. doi:10.1158/0008-5472.CAN-11-2762. PMC 3319846. PMID 22350413.
  11. ^ Paravicini G, Steinmayr M, Andre E, Becker-Andre M (October 1996). "The metastasis suppressor candidate nucleotide diphosphate kinase NM23 specifically interacts with members of the ROR/RZR nuclear orphan receptor subfamily". Biochem. Biophys. Res. Commun. 227 (1): 82–7. doi:10.1006/bbrc.1996.1471. PMID 8858107.
  12. ^ a b "Entrez Gene: RORA RAR-related orphan receptor A".

Further reading

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Category:Intracellular receptors Category:Transcription factors


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