PTGDR

PTGDR encodes the prostanoid DP1 receptor, a G protein-coupled receptor for prostaglandin D2 that acts as a tumor suppressor in the intestine: homozygous Ptgdr loss in ApcMin/+ mice raised intestinal tumor numbers by 30–40% without altering microvessel density or tumor cell proliferation, indicating a suppressive role independent of angiogenesis and proliferative rate (PMID:24729479). In a neuronal context, PTGDR participates in the control of cell survival and proliferation, where its knockdown shifts hippocampal neuronal cells toward reduced apoptosis (lower Bax, higher Bcl-2) and increased proliferation, placing it as a direct downstream target of miR-592-5p under hypoxic-ischemic conditions (PMID:29402808). Much of the characterized biology concerns transcriptional control of the gene rather than its receptor signaling: PTGDR expression is induced by all-trans retinoic acid through RARα binding to RARE sequences in the promoter in a haplotype-dependent manner, with the CTCT (-549T) variant showing stronger induction than CCCC, and ATRA-driven PTGDR overexpression altering IL-4 and IL-6 secretion (PMID:27373883, PMID:30986261). Promoter function is further shaped by the -613C>T polymorphism, which alters transcription factor binding affinity, and by differential DNA methylation associated with elevated expression in asthmatic patients (PMID:21883277). The receptor's own downstream G protein signaling and ligand-binding mechanism are not characterized in the available corpus.

1. 2011 Medium

   Established that common PTGDR promoter variation and epigenetic state, not just coding sequence, govern its expression level, linking the gene to inflammatory disease risk.

   Evidence EMSA of promoter variants plus methylation and expression profiling in asthmatic patients versus controls

   PMID:21883277

   Open questions at the time

   • The specific transcription factor binding differentially to the -613C/T allele was not identified
   • Causal link between methylation change and the 2.34-fold expression increase not established
   • Does not address receptor signaling output
2. 2014 High

   Demonstrated that the DP1 receptor mediates PGD2-driven tumor suppression in vivo, defining a protective function in intestinal tumorigenesis.

   Evidence Ptgdr knockout in ApcMin/+ mice with tumor counting and MYC mRNA measurement across multiple cohorts

   PMID:24729479

   Open questions at the time

   • Mechanism of suppression unresolved — proliferation and microvessel density were ruled out
   • Colon tumors were unaffected, leaving tissue specificity unexplained
   • Downstream G protein effectors not identified
3. 2016 Medium

   Showed that retinoic acid activates the PTGDR promoter in a haplotype-dependent manner, connecting RA signaling to PTGDR transcriptional control.

   Evidence Luciferase reporter assays of promoter variants in ATRA-treated A549 cells with in silico RARE identification

   PMID:27373883

   Open questions at the time

   • Direct RAR binding not demonstrated in this study (in silico RARE only)
   • Physiological relevance of A549 reporter activity to native PTGDR locus unclear
4. 2019 Medium

   Identified RARα as the direct transcriptional activator binding the PTGDR promoter and linked PTGDR levels to cytokine output, mechanistically grounding the RA-haplotype relationship.

   Evidence ChIP confirming RARα promoter binding, luciferase reporters, and cytokine bead arrays in patient PBMCs with ATRA/RAR antagonist treatment

   PMID:30986261

   Open questions at the time

   • Mechanism by which haplotype alters RARα binding affinity not resolved
   • Causal chain from PTGDR level to IL-4/IL-6 secretion not dissected
   • Receptor signaling downstream of PGD2 not addressed
5. 2018 Medium

   Placed PTGDR downstream of miR-592-5p as a regulator of neuronal apoptosis and proliferation under hypoxic-ischemic stress, extending its role beyond inflammation and tumor biology.

   Evidence siRNA knockdown and miR-592-5p mimic/inhibitor transfection with apoptosis, cell-cycle, and proliferation readouts in mouse hippocampal neuronal cells

   PMID:29402808

   Open questions at the time

   • Direct miR-592-5p:PTGDR target interaction shown phenotypically but binding-site validation not detailed
   • Signaling pathway linking PTGDR to Bax/Bcl-2 regulation not defined
   • In vivo neuronal relevance not tested

• How the DP1 receptor transduces the PGD2 signal — its G protein coupling, second messengers, and the molecular link to its tumor-suppressive and apoptotic outputs — remains uncharacterized in the available corpus.
• No ligand-binding or G protein coupling data
• No structural model
• Downstream effectors of tumor suppression unknown