Affinage

MREG

Melanoregulin · UniProt Q8N565

Length
214 aa
Mass
24.9 kDa
Annotated
2026-06-10
13 papers in source corpus 9 papers cited in narrative 11 extracted findings
Cross-family judge vs UniProt: Affinage preferred faithfulness: 5/5 claims corpus-supported (100%)

Mechanistic narrative

Synthesis pass · prose summary of the discoveries below

MREG (melanoregulin), encoded by the murine dilute suppressor (dsu) locus, is a vertebrate-specific small protein that regulates vesicular trafficking events underlying melanosome biogenesis and lysosomal maturation (PMID:3410303, PMID:3141922, PMID:19240024). Originally identified genetically, loss-of-function dsu mutation suppresses the coat-color dilution of dilute, ashen, and leaden by restoring normal dendritic melanocyte morphology, acting as a trans-acting suppressor specific to melanocyte-morphology-based pigmentation mutations (PMID:3410303, PMID:3141922, PMID:2379821); positional cloning showed it functions in an MYO5A-independent pathway to control pigment incorporation into hair (PMID:15550542). In retinal pigment epithelium, MREG localizes to small intracellular vesicles, associates with the endosomal phosphoinositide PI(3,5)P2, and is required for lysosome-dependent phagosome degradation, cathepsin D processing and activity, and intracellular cathepsin D homeostasis; its loss causes phagosome and A2E lipofuscin accumulation (PMID:19240024, PMID:23611523). MREG interacts with HPS BLOC-2 complex members and the Oa1 receptor to control melanosome size, providing a mechanistic link between the BLOC pathway and Oa1, where it acts from cytoplasmic vesicles rather than from melanosomes themselves (PMID:22984402). In cancer cells, MREG suppresses malignant behavior by acting upstream of PI3K/Akt-mTOR signaling, reducing Akt and mTOR phosphorylation, invasion and proliferation (PMID:28698135), and is silenced by the E2F1/miR-224-5p axis to promote migration, invasion and EMT (PMID:35126724).

Mechanistic history

Synthesis pass · year-by-year structured walk · 8 steps
  1. 1988 High

    Established that a distinct trans-acting locus (dsu) could genetically rescue melanocyte-morphology defects caused by mutations at unlinked pigmentation loci, defining MREG as a suppressor of the dilute pathway.

    Evidence Genetic mapping and histological melanocyte morphology analysis in compound mutant mice, including suppression of a defined dilute deletion allele

    PMID:3141922 PMID:3410303

    Open questions at the time
    • Molecular identity of the dsu gene product unknown at this stage
    • Biochemical mechanism of suppression undefined
  2. 1990 High

    Defined the specificity of MREG action by showing it suppresses only pigmentation mutations arising from abnormal melanocyte morphology, distinguishing a single coherent trafficking pathway from other pigmentation mechanisms.

    Evidence Genetic epistasis testing across 14 additional coat-color mutations spanning 11 loci in mice

    PMID:2379821

    Open questions at the time
    • Did not identify the gene or protein
    • Molecular pathway components unknown
  3. 2004 High

    Identified the dsu gene as MREG, a vertebrate-specific protein, and placed it in an MYO5A-independent pathway controlling pigment incorporation into hair, resolving the long-standing molecular identity of the suppressor.

    Evidence Positional cloning of the dsu locus combined with genetic epistasis and complementation in MYO5A-deficient and suppressor mouse backgrounds

    PMID:15550542

    Open questions at the time
    • Direct molecular partners of MREG not identified
    • Biochemical activity of the protein undefined
  4. 2009 High

    Extended MREG function beyond pigmentation by showing it is required for lysosome-dependent phagosome degradation and cathepsin D maturation in RPE, linking the protein to vesicular trafficking and lysosome maturation.

    Evidence Mreg-/- mouse phenotyping, cathepsin D activity assays in human and mouse RPE, A2E quantification, vesicle localization and PI(3,5)P2 binding assays

    PMID:19240024

    Open questions at the time
    • Mechanism by which MREG promotes cathepsin D processing unresolved
    • Direct effector of PI(3,5)P2 binding not defined
  5. 2012 High

    Provided a mechanistic link in melanosome biogenesis by showing MREG interacts with HPS BLOC-2 members and the Oa1 receptor to control melanosome size, acting from cytoplasmic vesicles rather than melanosomes.

    Evidence Genetic epistasis with Mreg knockout/transgenic mice crossed into BLOC-2 mutant and Oa1 knockout backgrounds, transgenic rescue, immunolocalization, and melanosome size quantification

    PMID:22984402

    Open questions at the time
    • Biochemical nature and stoichiometry of the BLOC-2 and Oa1 interactions not characterized
    • Whether interactions are direct unresolved
  6. 2013 Medium

    Refined the lysosomal role by showing MREG loss enhances secretion of intermediate cathepsin D and disrupts intracellular cathepsin D homeostasis, with concomitant basal laminin accumulation.

    Evidence Cathepsin D secretion/activity assays, Western blot for cathepsin D isoforms, and laminin immunostaining in Mreg(dsu/dsu) mouse RPE

    PMID:23611523

    Open questions at the time
    • Mechanistic basis for mis-secretion versus retention unclear
    • Causal relationship to laminin accumulation not established
  7. 2017 Medium

    Implicated MREG as a regulator of growth signaling by placing it upstream of PI3K/Akt-mTOR, where it suppresses cancer cell invasion and proliferation.

    Evidence MREG overexpression and knockdown in thyroid cancer cell lines with phospho-Akt/mTOR Western blots, invasion/proliferation assays, and pharmacological rescue with dactolisib

    PMID:28698135

    Open questions at the time
    • Molecular link between MREG and PI3K/Akt-mTOR not defined
    • Whether this connects to the vesicular trafficking role unknown
  8. 2022 Medium

    Positioned MREG within a transcriptional/microRNA regulatory axis, showing it is suppressed by E2F1/miR-224-5p and its restoration attenuates migration, invasion and EMT in hepatocellular carcinoma.

    Evidence miRNA target validation (TargetScan/miRDB/StarBase), MREG overexpression in HCC cell lines, migration/invasion assays, EMT marker analysis, and rescue experiments

    PMID:35126724

    Open questions at the time
    • Direct luciferase confirmation of binding not specified
    • Downstream effectors mediating EMT suppression not identified

Open questions

Synthesis pass · forward-looking unresolved questions
  • The biochemical activity of MREG and how a single small vesicular protein mechanistically couples melanosome biogenesis, lysosomal cathepsin D maturation, and PI3K/Akt-mTOR signaling remains unresolved.
  • No defined enzymatic or structural mechanism for the protein
  • No unifying molecular model linking trafficking and growth-signaling roles
  • Direct versus indirect nature of reported partner interactions not established

Mechanism profile

Synthesis pass · controlled-vocabulary classification · explore literature graph →
Molecular activity
GO:0008289 lipid binding 1
Localization
GO:0031410 cytoplasmic vesicle 2 GO:0005768 endosome 1
Pathway
R-HSA-9609507 Protein localization 2 R-HSA-162582 Signal Transduction 1
Partners
OA1

Evidence

Reading pass · 11 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
1988 The murine dilute suppressor gene dsu (encoding MREG) suppresses the coat-color dilution of dilute (d), ashen (ash), and leaden (ln) mutations by restoring normal dendritic melanocyte morphology, acting as a semidominantly inherited trans-acting suppressor unlinked to the d, ash, or ln loci. Genetic mapping and histological examination of melanocyte morphology in compound mutant mice Genetics High 3141922 3410303
1988 dsu/MREG does not function like retrotransposon-insertion suppressors in yeast/Drosophila; it suppresses a deletion allele (dl20J) of dilute, indicating a distinct mechanism of suppressor action, and is semidominantly inherited. Genetic complementation and coat-color suppression testing with a defined deletion allele Proceedings of the National Academy of Sciences of the United States of America Medium 3141922
1990 dsu/MREG suppression is specific to coat-color mutations that result from abnormal melanocyte morphology (d, ln, ash, ruby-eye, ruby-eye-2); it does not suppress mutations acting through other pigmentation mechanisms, indicating pathway-specific action on neural crest-derived melanocytes. Genetic epistasis testing with 14 additional coat-color mutations across 11 loci in mice Genetics High 2379821
2004 dsu is caused by a loss-of-function mutation in a unique vertebrate-specific protein (MREG/melanoregulin) that functions in an MYO5A-independent pathway to alter pigment incorporation into the hair. MYO5A is nonessential for melanosome transfer to keratinocytes, though it is required for peripheral melanosome accumulation in melanocytes. Positional cloning of dsu locus; genetic and cell biological analysis of MYO5A-deficient mice; complementation and coat-color suppression assays Proceedings of the National Academy of Sciences of the United States of America High 15550542
2009 MREG is required for lysosome-dependent phagosome degradation in retinal pigment epithelial (RPE) cells; loss of MREG results in phagosome accumulation (delayed degradation), accumulation of lipofuscin component A2E over time, and defective processing/diminished activity of lysosomal hydrolase cathepsin D. Mreg−/− mouse phenotypic analysis; cathepsin D activity assay in MREG-deficient human and mouse RPE cells; A2E quantification The Journal of biological chemistry High 19240024
2009 MREG localizes to small intracellular vesicles in RPE cells and associates with the endosomal phosphoinositide phosphatidylinositol 3,5-bisphosphate (PI(3,5)P2), consistent with a role in intracellular trafficking and lysosome maturation. Subcellular fractionation, vesicle localization imaging, and phosphoinositide binding assay The Journal of biological chemistry Medium 19240024
2012 MREG interacts with members of the HPS BLOC-2 complex and with Oa1 (ocular albinism type 1 receptor) to regulate melanosome size; loss of MREG function increases the size of micromelanosomes in BLOC-2 mutant choroid, while transgenic overexpression of MREG corrects the macromelanosome size defect in Oa1 knockout RPE. This provides the first mechanistic link between the BLOC pathway and Oa1 in melanosome biogenesis. Genetic epistasis using Mreg knockout and MREG transgenic mice crossed with BLOC-2 mutants (ruby, ruby2, cocoa) and Oa1 knockout; immunohistochemical localization of MREG; melanosome size quantification PloS one High 22984402
2012 MREG localizes not to melanosomes themselves but to small vesicles in the cytoplasm of RPE cells, consistent with a role in regulating membrane interactions during melanosome biogenesis rather than direct melanosome association. Immunohistochemical analysis of RPE cell ultrastructure in Mreg transgenic and knockout mice PloS one Medium 22984402
2013 Loss of MREG enhances secretion of intermediate cathepsin D (48 kDa) from RPE cells, resulting in increased extracellular cathepsin D activity; MREG is required to maintain intracellular cathepsin D homeostasis. Loss of Mreg(dsu) allele also leads to increased basal laminin accumulation in the RPE. Cathepsin D secretion and activity assay in Mreg(dsu/dsu) mouse RPE; Western blot for cathepsin D isoforms; laminin immunostaining Visual neuroscience Medium 23611523
2017 MREG overexpression decreases phosphorylation of Akt and mTOR in thyroid cancer cells, suppressing their invasion and proliferation; MREG knockdown has the opposite effect. The mTOR inhibitor dactolisib abrogates the pro-invasive/proliferative effect of MREG knockdown, placing MREG upstream of PI3K/Akt-mTOR signaling. MREG overexpression and knockdown in thyroid cancer cell lines; Western blot for phospho-Akt and phospho-mTOR; invasion and proliferation assays; pharmacological rescue with dactolisib Biochemical and biophysical research communications Medium 28698135
2022 MREG is a direct target of miR-224-5p in hepatocellular carcinoma cells; overexpression of MREG attenuates liver cancer cell migration, invasion, and epithelial-mesenchymal transition (EMT). The E2F1/miR-224-5p axis suppresses MREG to promote these malignant behaviors. Luciferase reporter or bioinformatic target validation (TargetScan, miRDB, StarBase); MREG overexpression in HCC cell lines; migration/invasion assays; EMT marker analysis; rescue experiments Oncology letters Medium 35126724

Source papers

Stage 0 corpus · 13 papers · ranked by NIH iCite citations
Year Title Journal Citations PMID
1988 The murine dilute suppressor gene dsu suppresses the coat-color phenotype of three pigment mutations that alter melanocyte morphology, d, ash and ln. Genetics 56 3410303
2004 dsu functions in a MYO5A-independent pathway to suppress the coat color of dilute mice. Proceedings of the National Academy of Sciences of the United States of America 42 15550542
2009 Melanoregulin (MREG) modulates lysosome function in pigment epithelial cells. The Journal of biological chemistry 41 19240024
1988 Dilute suppressor dsu acts semidominantly to suppress the coat color phenotype of a deletion mutation, dl20J, of the murine dilute locus. Proceedings of the National Academy of Sciences of the United States of America 32 3141922
1990 Interaction of the murine dilute suppressor gene (dsu) with fourteen coat color mutations. Genetics 25 2379821
2019 Characterization of the Angiogenic Potential of Human Regulatory Macrophages (Mreg) after Ischemia/Reperfusion Injury In Vitro. Stem cells international 16 31341483
2017 MREG suppresses thyroid cancer cell invasion and proliferation by inhibiting Akt-mTOR signaling. Biochemical and biophysical research communications 15 28698135
2022 E2F1-induced microRNA-224-5p expression is associated with hepatocellular carcinoma cell migration, invasion and epithelial-mesenchymal transition via MREG. Oncology letters 13 35126724
2023 Large extracellular vesicles derived from human regulatory macrophages (L-EVMreg) attenuate CD3/CD28-induced T-cell activation in vitro. Journal of molecular medicine (Berlin, Germany) 9 37725101
2013 Loss of melanoregulin (MREG) enhances cathepsin-D secretion by the retinal pigment epithelium. Visual neuroscience 9 23611523
2012 Melanoregulin, product of the dsu locus, links the BLOC-pathway and OA1 in organelle biogenesis. PloS one 9 22984402
2023 Characterization of large extracellular vesicles (L-EV) derived from human regulatory macrophages (Mreg): novel mediators in wound healing and angiogenesis? Journal of translational medicine 8 36717876
2024 Effects of temporal IFNγ exposure on macrophage phenotype and secretory profile: exploring GMP-Compliant production of a novel subtype of regulatory macrophages (MregIFNγ0) for potential cell therapeutic applications. Journal of translational medicine 5 38835045

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