CHRM2

CHRM2 encodes the M2 muscarinic acetylcholine receptor and shows cell-type- and tissue-specific deployment: in human airway smooth muscle its transcription is driven by a TATA-less promoter containing Sp1, GATA, and AP-2 elements together with a functionally active CA tandem repeat and multiple transcription start sites (PMID:14512373), and in primate prefrontal and anterior cingulate cortex its expression is selectively enriched in deep-layer excitatory neurons and PVALB+ inhibitory neurons, a distribution distinct from CHRM1 and CHRM3 [PMID:bio_10.1101_2025.05.23.655820]. A heritable structural variant of the receptor links CHRM2 to cardiac disease: the C722G (Cys176Trp) missense mutation co-segregates with familial dilated cardiomyopathy and is accompanied by anti-CHRM2 autoantibodies in carriers (PMID:18451336), and when expressed in cells this mutant remodels the proteome across cytoskeletal, metabolic, and stress-response programs, enriching apoptosis- and immune-associated networks (FOS, BAX, MYC, TP53, IL6) (PMID:23743182). Beyond signaling, CHRM2 controls cellular metabolism in cancer, promoting aerobic glycolysis and suppressing apoptosis in lung adenocarcinoma, where its direct ligand β-sitosterol reverses these effects by inhibiting glycolysis and inducing apoptosis (PMID:39537174). The receptor's canonical ligand-coupled signal transduction mechanism is not detailed in the available corpus.

1. 2003 Medium

   Defined how CHRM2 transcription is controlled in airway smooth muscle, establishing the cis-regulatory architecture governing receptor expression in a relevant tissue.

   Evidence 5' RACE and reporter gene assays in primary human airway smooth muscle and BEAS-2B cells

   PMID:14512373

   Open questions at the time

   • Trans-acting factors actually binding Sp1/GATA/AP-2 sites not confirmed in vivo
   • No link drawn between promoter activity and receptor signaling output
   • Tissue specificity of the CA repeat effect not generalized
2. 2008 Medium

   Connected a specific CHRM2 structural variant to human cardiac disease, raising the question of whether a receptor mutation drives autoimmune cardiomyopathy.

   Evidence Direct sequencing, linkage/co-segregation analysis, and ELISA autoantibody serology in DCM families

   PMID:18451336

   Open questions at the time

   • No in vitro reconstitution of mutant receptor function
   • Causal mechanism linking mutation to autoantibody production unresolved
   • Single-lab family cohort
3. 2013 Medium

   Asked what downstream cellular consequences the Cys176Trp mutation produces, revealing a broad proteomic remodeling toward apoptotic and cytoskeletal pathways.

   Evidence Lentiviral WT/mutant CHRM2 overexpression in CHO cells with label-free proteomics and STRING analysis

   PMID:23743182

   Open questions at the time

   • Individual protein changes not functionally validated
   • Heterologous CHO system may not reflect cardiomyocyte biology
   • Signaling pathway linking receptor to proteome shift not defined
4. 2024 Medium

   Established a metabolic role for CHRM2 in cancer and identified β-sitosterol as a direct ligand, addressing whether the receptor controls aerobic glycolysis.

   Evidence Network pharmacology, lentiviral overexpression, Seahorse ECAR/OCR, glycolysis metabolite assays, and in vivo homograft mouse model in lung adenocarcinoma

   PMID:39537174

   Open questions at the time

   • Direct binding inferred from network pharmacology rather than biophysical assay
   • Downstream effectors coupling CHRM2 to glycolytic machinery not identified
   • Single lab
5. 2025 Medium

   Mapped CHRM2 to specific cortical neuron populations, addressing where the receptor acts within brain circuits relative to other muscarinic subtypes.

   Evidence Single-nucleus RNA sequencing and mRNA-protein histology in macaque prefrontal and anterior cingulate cortex (preprint)

   PMID:bio_10.1101_2025.05.23.655820

   Open questions at the time

   • Functional consequence of cell-type enrichment not established
   • Human relevance of macaque distribution not confirmed
   • Preprint, not peer-reviewed

• The canonical ligand-activated G-protein signaling mechanism of the M2 receptor and how it integrates with the metabolic and disease phenotypes remains uncharacterized in this corpus.
• No direct characterization of receptor-G protein coupling in the timeline
• Mechanistic link between cardiac autoimmunity and cancer metabolism not established
• No structural data on the receptor