Biology:Prostaglandin DP2 receptor

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Short description: Protein-coding gene in the species Homo sapiens


A representation of the 3D structure of the protein myoglobin showing turquoise α-helices.
Generic protein structure example


Prostaglandin D2 receptor 2 (DP2 or CRTH2) is a human protein encoded by the PTGDR2 gene and GPR44.[1] DP2 has also been designated as CD294 (cluster of differentiation 294). It is a member of the class of prostaglandin receptors which bind with and respond to various prostaglandins. DP2 along with Prostaglandin DP1 receptor are receptors for prostaglandin D2 (PGD2). Activation of DP2 by PGD2 or other cognate receptor ligands has been associated with certain physiological and pathological responses, particularly those associated with allergy and inflammation, in animal models and certain human diseases.

Gene

The PTGDR2 gene is located on human chromosome 11 at position q12.2 (i.e. 11q12.2). It consists of two introns and three exons and codes for a G protein coupled receptor (GPCR) composed of 472 amino acids. DP2, is related to members of the chemotactic factor class of GPCRs, sharing an amino acid sequence identity of 29% with the C5a receptor, Formyl peptide receptor 1, and Formyl peptide receptor 2 receptors. DP2 has little or no such amino acid sequence relationship to the eight other Prostanoid receptors (see Eicosanoid receptor).[2][3]

Expression

DP2 was found to stimulate the directed movement or chemotaxis of human T-helper type 2 cells (see T helper cell) by binding to a receptor initially termed GPR44 and thereafter CRTH2 (for Chemoattractant Receptor-homologous molecule expressed on T-Helper type 2 cells). In addition to these T helper cells, DP2 messenger RNA is also expressed by human basophils, eosinophils, a subpopulation of cytotoxic T cells (i.e. CD8+ T cells), thalamus, ovary, and spleen, and, in the central nervous system, by the frontal cortex, pons, hippocampus, and at lower levels, hypothalamus and caudate nucleus/putamen. These transcripts are also detected in fetal liver and thymus.[4][3][5]

Ligands

Activating ligands

The following standard prostaglandins have the following relative affinities and potencies in binding to and activating DP2: PGD2>>PGF2alpha=PGE2>PGI2=thromboxane A2. The cyclopentenone prostaglandins, PGJ2, Δ12-PGJ2, and 15-d-Δ12,14-PGJ2 are spontaneously formed or protein-facilitated derivatives of PGD2 that are generated in vitro as well as in vivo; these derivatives have binding affinities and activating potencies on DP2 that are similar to PGD2. Studies suggest that at least some if not most or all of the cytotoxic effects of cylopenenone prostaglandin derivatives of PGD2 act independently of DP2. Certain metabolites and derivatives of PGD2 viz., 13,14-dihydro-15-keto-PGD2 and 15(S)-15-methyl-PGD2, are ~10-fold less active than PGD2 while the drug indomethacin is weak in activating DP2.[5]

Inhibiting ligands

The following compounds are selective receptor antagonists of and thereby inhibit the activation of DP2: fevipiprant, setipiprant, ADC-3680, AZD-1981, MK-1029, MK-7246, OC-459, OC000459, QAV-680, and TM30089. Ramatroban and vidupiprant are non-selective (i.e. known to influence other receptors) antagonists of DP2.[5]

Mechanisms of cell activation

G protein-coupled receptors (GPCRs) such as DP2 are integral membrane proteins that, when bound by their cognate ligands (or, in some cases, even when not ligand-bound and thereby acting continuously in a constitutive manner {see Receptor (biochemistry)}), mobilize one or more types of Heterotrimeric G proteins. DP2 is classified as a "contractile" prostanoid receptor in that it can cause the contraction of smooth muscle. As evidenced by its initial discovery as a receptor for PGD2 in T-helper type 2 cells, activated DP2 triggers Gi alpha subunit-linked heterotrimeric G proteins to dissociate into their component a) Gi alpha subunits (also termed Giα subunits) inhibit adenylyl cyclase b) G beta-gamma complex of subunits (Gβγ) have many potential functions, including simulation of phospholipase C to cleave phosphatidylinositol triphosphate into inositol triphosphate (IP3) and diacylglycerol (DAG), inhibition or stimulation of adenylyl cyclase depending on the isoform, activation of GIRK channels and activation of GRK. IP3 raises cytosolic Ca2 levels thereby regulating Ca2-sensitive signal pathways; DAG activates certain protein kinase C enzymes )PKCs) that phosphorylate and thereby regulate target proteins involved in cell signaling; and adenyl cyclase converts AMP into cyclic AMP (cAMP) thereby down-regulating cAMP-responsive proteins involved in cell signalling.[6][7] Concurrently with the mobilization of these pathways, activated DP2 also mobilizes G protein-coupled receptor kinases (GRKs, GRK2, GRK3, and/or GRK6) and Arrestin-2 (also termed Arrestin beta 1 or β-arrestin). The GRKs, along with the DAG-activated PKCs, phosphorylate DP2 to promote its internalization while arrestin-2 inhibits DP2 from further activating heterotrimeric G proteins while also linking DP2 to elements, clathrin and clathrin adaptor AP2, of the receptor internalization machinery. These pathways render DP2 unable to mobilize heterotrimereic G proteins[8] thereby rendering the cell less sensitive or insensitive to further stimulation by DP ligands. The process, termed Homologous desensitization, serves as a physiological limiter of cell responses to DP2 activators.[8][9][10]

Function

Allergy

Ligands that activate DP2 stimulate the in vitro chemotaxis (i.e. directed migration) of leukocytes active in mediating allergic responses viz., eosinophils, basophils, and Th2 cells. DP2 activation also stimulates eosinophils and basophils to release the many pro-allergic elements of their granules to the extracellular milieu.[6] Ligand-induced activation of DP2 has similar activities in vivo it stimulates the accumulation on and activation of eosinophils, basophils, and Th2 cells at sites of nascent inflammation in animal models.[7] PGD2, acting through DP2, stimulates the in vitro chemotaxis of CD8+ cells, although the contribution of this to the in vivo function of DP2 has not been clarified.[11]

PDP2 receptor antagonists have been shown to allergic reactions induced in the airways mice and sheep as well as the airways and nose of guinea pigs.[11]

Mice genetically engineered to be deficient in DP2 (i.e. DP2−/-) mice are defective in mounting asthmatic responses in models of: a) allergen-induced asthma, b) dermal allergy, c) ACTH and cortisol release in response to inflammatory stimuli, and c) perception of pain caused by inflammation in peripheral tissues.[6][7][12] DP2−/- mice are also highly resistant to the gram (-) bacterial sepsis caused by cecal ligation and puncture; the protective effect was associated with lower bacterial load and lower production of pro-inflammatory cytokines (i.e. TNF-α, IL-6, and CCL3) and increased production of an anti-inflammatory cytokine (IL-10).[4]

Embryogenesis

Studies in Dp2 gene-deficient (i.e. Dp2−/-) mice indicate that DP2 is essential for controlling cell cycle genes in fetal testes which contribute to the arrest of mitotic process and to the differentiate of germ cells. This control involves, at least in part, the DP2-dependent activation of the male germ cell marker Nanos2 and the inhibition of meiosis through repression of Stra8.[13]

Human genomics studies

The 1544G-1651G haplotype in the 3'-Untranslated region of the DP2 gene increased the stability of the gene's mRNA; this haplotype has been associated with an increased incidence of asthma in Chinese population and African but not Japanese sampling studies.[14][15] The rs11571288 C/G Single-nucleotide polymorphism (SNP) variant[16] of DP2 has been associated with an increase in the percentage of circulating eosinophils, an increase in the expression of DP2 by these cells, an enhanced rate of differentiation of precursor cells to Th2 cells in culture, enhanced Th2 cytokine (i.e. IL-4 and IL-13) production by these cells, and an increased incidence of asthma in a sampling of multi-ethnic Caucasian Canadians.[14][17]

Clinical studies

Allergic Diseases

Setipiprant (ACT-129968), a selective, orally active antagonist of the (DP2) receptor, proved to be well tolerated and reasonably effective in reducing allergen-induced airway responses in asthmatic patient clinical trials.[18][19] However, the drug, while supporting the concept that DP2 contributes to asthmatic disease, did not show sufficient advantage over existing drugs and was discontinued from further development for this application (see setipiprant).[20]

Patients with the chronic spontaneous urticarial form of hives exhibit significantly lower surface membrane expression of the DP22 receptor on their blood eosinophils and basophils, a result fully consistent with this receptor being initially activated and subsequently desensitization (refer to above section on "Mechanisms of cell activation").[21] The DP2 receptor antagonist, AZD1981, is in a phase 2 clinical trial for the treatment of chronic idiopathic urticarial.[22]

A randomized, partially-blinded, placebo-controlled, two-way crossover, proof of concept study comparing the efficacy of the DP2 receptor antagonist, QAV680, in the treatment of allergic rhinitis[23] and a study on the effectiveness of OC000459, a DP2 receptor antagonist, in reducing the exacerbation of asthma induced by experimentally-induced rhinovirus infection in subjects[24] has just been completed or is underway, respectively.

Other diseases and conditions

Baldness

Acting through DP2, PGD2 can inhibit hair growth, suggesting that this receptor is a potential target for bald treatment.[25] A potential drug for blocking the DP2 receptor and thereby ameliorating baldness is the compound setipiprant.[26] A phase 2A study is underway to evaluate the safety, tolerability, and efficacy of oral setipiprant relative to a placebo in 18- to 49-year-old males with androgenetic alopecia.[27]

See also

References

  1. ↑ "Entrez Gene: GPR44 G protein-coupled receptor 44". https://www.ncbi.nlm.nih.gov/sites/entrez?Db=gene&Cmd=ShowDetailView&TermToSearch=11251. 
  2. ↑ "PTGDR2 prostaglandin D2 receptor 2". https://www.ncbi.nlm.nih.gov/gene?cmd=Retrieve&dopt=full_report&list_uids=11251. 
  3. ↑ 3.0 3.1 "Discovery of three novel orphan G-protein-coupled receptors". Genomics 56 (1): 12–21. 1999. doi:10.1006/geno.1998.5655. PMID 10036181. 
  4. ↑ 4.0 4.1 "CRTH2 is a critical regulator of neutrophil migration and resistance to polymicrobial sepsis". Journal of Immunology 188 (11): 5655–64. 2012. doi:10.4049/jimmunol.1102330. PMID 22544936. 
  5. ↑ 5.0 5.1 5.2 "DP2 receptor - Prostanoid receptors - IUPHAR/BPS Guide to PHARMACOLOGY". http://www.guidetopharmacology.org/GRAC/ObjectDisplayForward?objectId=339. 
  6. ↑ 6.0 6.1 6.2 "Role of prostaglandin D(2) and its receptors in the pathophysiology of asthma". Allergology International 57 (4): 307–12. 2008. doi:10.2332/allergolint.08-RAI-0033. PMID 18946232. 
  7. ↑ 7.0 7.1 7.2 "Prostaglandins and inflammation". Arteriosclerosis, Thrombosis, and Vascular Biology 31 (5): 986–1000. 2011. doi:10.1161/ATVBAHA.110.207449. PMID 21508345. 
  8. ↑ 8.0 8.1 "Prostanoid receptors and acute inflammation in skin". Biochimie 107 Pt A: 78–81. 2014. doi:10.1016/j.biochi.2014.08.010. PMID 25179301. 
  9. ↑ "Characterization of C-terminal tail determinants involved in CRTH2 receptor trafficking: identification of a recycling motif". European Journal of Pharmacology 630 (1–3): 10–8. 2010. doi:10.1016/j.ejphar.2009.12.022. PMID 20035740. 
  10. ↑ "Cyclooxygenase pathways". Acta Biochimica Polonica 61 (4): 639–49. 2014. doi:10.18388/abp.2014_1825. PMID 25343148. 
  11. ↑ 11.0 11.1 "The role of prostaglandins in allergic lung inflammation and asthma". Expert Review of Respiratory Medicine 9 (1): 55–72. 2015. doi:10.1586/17476348.2015.992783. PMID 25541289. 
  12. ↑ "The roles of prostanoids in infection and sickness behaviors". Journal of Infection and Chemotherapy 14 (4): 270–8. 2008. doi:10.1007/s10156-008-0622-3. PMID 18709530. 
  13. ↑ "Multiple roles of the prostaglandin D2 signaling pathway in reproduction". Reproduction 149 (1): R49–58. 2015. doi:10.1530/REP-14-0381. PMID 25269616. 
  14. ↑ 14.0 14.1 "Pharmacogenomics of Prostaglandin and Leukotriene Receptors". Frontiers in Pharmacology 7: 316. 2016. doi:10.3389/fphar.2016.00316. PMID 27708579. 
  15. ↑ "Genetic impact of functional single nucleotide polymorphisms in the 3'-UTR region of the chemoattractant receptor expressed on Th2 cells (CRTH2) gene on asthma and atopy in a Japanese population". International Archives of Allergy and Immunology 142 (1): 51–8. 2007. doi:10.1159/000095998. PMID 17016057. 
  16. ↑ "No items found - Gene - NCBI". https://www.ncbi.nlm.nih.gov/gene/?term=RS11571288. 
  17. ↑ "The single nucleotide polymorphism CRTh2 rs533116 is associated with allergic asthma and increased expression of CRTh2". Allergy 67 (11): 1357–64. 2012. doi:10.1111/all.12003. PMID 22947041. 
  18. ↑ "Setipiprant, a selective CRTH2 antagonist, reduces allergen-induced airway responses in allergic asthmatics". Clinical & Experimental Allergy 44 (8): 1044–52. 2014. doi:10.1111/cea.12357. PMID 24964348. 
  19. ↑ "Single- and multiple-dose tolerability and pharmacokinetics of the CRTH2 antagonist setipiprant in healthy male subjects". Fundamental & Clinical Pharmacology 28 (6): 690–9. 2014. doi:10.1111/fcp.12079. PMID 24734908. 
  20. ↑ "Update on the status of DP2 receptor antagonists; from proof of concept through clinical failures to promising new drugs". Expert Opinion on Investigational Drugs 23 (1): 55–66. 2014. doi:10.1517/13543784.2013.839658. PMID 24073896. 
  21. ↑ "Altered expression of chemoattractant receptor-homologous molecule expressed on T(H)2 cells on blood basophils and eosinophils in patients with chronic spontaneous urticaria". The Journal of Allergy and Clinical Immunology 137 (1): 304–6. 2016. doi:10.1016/j.jaci.2015.06.004. PMID 26194547. 
  22. ↑ Efficacy and Safety of Chemoattractant Receptor-homologous Molecule Expressed on T Helper Type 2 (CRTh2) Antagonist AZD1981 in Chronic Idiopathic Urticaria (CIU) Antihistamines - Full Text View - ClinicalTrials.gov. 13 June 2017. https://clinicaltrials.gov/ct2/show/NCT02031679?term=prostaglandin+D2+receptor+2&rank=6. 
  23. ↑ Clinical trial number NCT00784732 for "A Study to Compare the Efficacy of QAV680 Against Placebo in Treating Seasonal Allergic Rhinitis in an Environmental Exposure Chamber" at ClinicalTrials.gov
  24. ↑ Clinical trial number NCT02660489 for "Effect of OC459 on the Response to Rhinovirus Challenge in Asthma" at ClinicalTrials.gov
  25. ↑ "Prostaglandin D2 inhibits hair growth and is elevated in bald scalp of men with androgenetic alopecia". Science Translational Medicine 4 (126): 126ra34. March 2012. doi:10.1126/scitranslmed.3003122. PMID 22440736. 
  26. ↑ "On the mechanism of interaction of potent surmountable and insurmountable antagonists with the prostaglandin D2 receptor CRTH2". Molecular Pharmacology 69 (4): 1441–53. April 2006. doi:10.1124/mol.105.017681. PMID 16418339. 
  27. ↑ Clinical trial number 2A Study of Setipiprant Tablets in Androgenetic Alopecia in Males NCT02781311Phase 2A Study of Setipiprant Tablets in Androgenetic Alopecia in Males at ClinicalTrials.gov

Further reading

External links

This article incorporates text from the United States National Library of Medicine, which is in the public domain.



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