Protein trafficking
How MC4R variants scramble receptor trafficking
Open access · cc by · source: Europe PMC
Obesity-linked MC4R mutations disrupt plasma-membrane localization, endocytosis and β-arrestin pathways beyond classical cAMP loss-of-function.
How this study connects
Role on claims
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MC4R homodimerizes and undergoes β-arrestin-2–driven endocytosis. Many variants impair trafficking even when cAMP looks normal; gain-of-function alleles link to obesity protection.
Evidence for the claim as stated.
Dozens of human MC4R variants were assayed for surface expression, endocytosis, dimerization, β-arrestin engagement and ERK/cAMP signalling. MC4R homodimerizes and undergoes β-arrestin-2–driven endocytosis; many variants impair trafficking even when cAMP looks normal, and gain-of-function alleles link to obesity protection. cAMP/reporter readouts can therefore miss trafficking-defective alleles. Cellular classification is not a clinical trial.
Evidence for the claim as stated.
MC4R shows that a cAMP/reporter signal can look normal while trafficking is impaired, so luciferase-like pathway readouts disagree with surface-expression assays. Foxp3 and ZFP36 papers barely use luciferase at all: DNA methylation/ChIP versus mRNA decay and metabolomics.
Evidence for the claim as stated.
Human MC4R variants were assayed in cells for surface expression, endocytosis/trafficking, dimerization, β-arrestin engagement and ERK/cAMP signalling. MC4R homodimerizes and undergoes β-arrestin-2–driven endocytosis; many variants impair trafficking even when cAMP looks normal, and gain-of-function alleles link to obesity protection. Any ELISA-format cAMP or ligand-binding plate is a supporting biochemistry assay, not the core trafficking microscopy, and cellular loss-of-function is not a clinical trial.
Evidence for the claim as stated.
The three tagged studies disagree about what an 'ELISA paper' would even be measuring. MC4R work is cellular receptor trafficking and cAMP/ERK; MDV work is shedding, infectious period (~2 weeks) and sentinel timing (~9 days earlier) in chickens; E. coli OMV work is NOD1/NOD2 ligands and epithelial barrier signalling. They share an immunoassay-shaped supporting assay at most, not a common antigen.
Evidence for the claim as stated.
Implications also conflict if someone treats every plate assay as the same. A normal cAMP well for an MC4R variant can hide a trafficking defect relevant to obesity genetics; a high viral titre after leaky vaccination can hide increased transmission of hyperpathogenic MDV; an epithelial cytokine bump after OMVs is not probiotic efficacy in patients.
Evidence for the claim as stated.
Open questions
Tensions this paper is part of
From concept pages' “where studies disagree.” Disagreement means the same question; scope means different assays, populations, or outcomes.
MC4R shows that a cAMP/reporter signal can look normal while trafficking is impaired, so luciferase-like pathway readouts disagree with surface-expression assays. Foxp3 and ZFP36 papers barely use luciferase at all: DNA methylation/ChIP versus mRNA decay and metabolomics.
The three tagged studies disagree about what an 'ELISA paper' would even be measuring. MC4R work is cellular receptor trafficking and cAMP/ERK; MDV work is shedding, infectious period (~2 weeks) and sentinel timing (~9 days earlier) in chickens; E. coli OMV work is NOD1/NOD2 ligands and epithelial barrier signalling. They share an immunoassay-shaped supporting assay at most, not a common antigen.
- Supports · Can leaky vaccines favor nastier viruses?
- Supports · How do E. coli vesicles talk to gut epithelium?
Implications also conflict if someone treats every plate assay as the same. A normal cAMP well for an MC4R variant can hide a trafficking defect relevant to obesity genetics; a high viral titre after leaky vaccination can hide increased transmission of hyperpathogenic MDV; an epithelial cytokine bump after OMVs is not probiotic efficacy in patients.
- Supports · Can leaky vaccines favor nastier viruses?
- Supports · How do E. coli vesicles talk to gut epithelium?
Study at a glance
- Design
- Animal / in-vitro — Cell assays of rare and common human MC4R variants for trafficking, dimerization, and signaling
- N
- N=48 · 48 rare obesity-associated MC4R variants plus two common protective alleles (V103I, I251L)
- Population
- Human MC4R variants expressed in cellular assays
- Outcome
- Endocytosis, trafficking, dimerization, and signaling consequences of MC4R variants
Structured fields used in claim comparison tables when every cited study has a complete layer.
Inspect source passages
How MC4R variants scramble receptor trafficking
These passages occur verbatim in the stored paper text. They support the points listed below; they do not verify every statement in the explanation.
Authors characterized 48 rare MC4R variants.
We characterized 48 rare MC4R variants (minor allele frequency [MAF], <1%) associated with severe obesity in clinically ascertained cohorts (; ; ) and two prevalent MC4R variants (MAF, 1%–2%; V103I and I251L) associated with protection from obesity in large population-derived studies (; ; ; ; A; ).
Up to 25% of MC4R mutations in obese cohorts do not reduce cAMP.
However, up to 25% of MC4R mutations found in obese cohorts do not reduce cAMP production and are therefore classified as wild-type (WT)-like/non-pathogenic ( https://www.mc4r.org.uk ; ).
Key findings
MC4R homodimerizes and undergoes β-arrestin-2–driven endocytosis. Many variants impair trafficking even when cAMP looks normal; gain-of-function alleles link to obesity protection.
Methodology
Authors assayed dozens of rare and common human MC4R variants for surface expression, endocytosis/trafficking, dimerization, β-arrestin engagement and ERK/cAMP signaling in cells.
Limitations
Cellular LoF classification is not a full clinical trial; mouse models are still needed for genotype–phenotype dissection.
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