Affinage

CHML

Rab proteins geranylgeranyltransferase component A 2 · UniProt P26374

Length
656 aa
Mass
74.1 kDa
Annotated
2026-04-28
10 papers in source corpus 5 papers cited in narrative 5 extracted findings

Mechanistic narrative

Synthesis pass · prose summary of the discoveries below

CHML encodes Rab escort protein 2 (REP-2), which binds newly synthesized Rab GTPases and is absolutely required for their geranylgeranylation by the Rab geranylgeranyltransferase complex; REP-2 shows activity comparable to REP-1 toward Rab1A, Rab5A, and Rab6 but reduced activity toward Rab3A/3D, with substrate specificity governed by the Rab C-terminal sequence (PMID:8294464). In hepatocellular carcinoma, CHML promotes metastasis by escorting Rab14 to membranes, enabling Rab14-positive vesicles carrying Mucin13 and CD44 to drive migration and invasion (PMID:31175290). CHML is transcriptionally activated by NRF2 through an antioxidant response element in its promoter and mediates mTOR translocation and activation at the lysosome (PMID:35184380).

Mechanistic history

Synthesis pass · year-by-year structured walk · 5 steps
  1. 1994 High

    Establishing that REP-2 is an essential cofactor for Rab geranylgeranylation resolved how newly synthesized Rab GTPases acquire their lipid anchors and revealed that REP-2 and REP-1 differ in substrate specificity, particularly toward Rab3A/3D, dictated by Rab C-terminal sequences.

    Evidence In vitro geranylgeranyl transferase assay with recombinant REP-2 and domain-swap mutagenesis of Rab C-termini

    PMID:8294464

    Open questions at the time
    • Structural basis of the REP-2/Rab interaction and how C-terminal residues determine selectivity was not resolved
    • Whether REP-2 has escort functions beyond prenylation (e.g., membrane delivery) was not directly tested
    • In vivo phenotype of REP-2 loss in mammalian systems was not assessed
  2. 2019 High

    Demonstrating that CHML escorts Rab14 to membranes in HCC cells, enabling vesicular transport of Mucin13 and CD44, established a specific post-prenylation escort function driving cancer metastasis.

    Evidence siRNA knockdown, overexpression, in vivo metastasis model, co-immunoprecipitation, and vesicle cargo identification in HCC cells

    PMID:31175290

    Open questions at the time
    • Whether CHML-dependent Rab14 recycling operates in normal hepatocytes or is specific to transformed cells
    • Mechanism by which Mucin13/CD44 are selectively loaded onto Rab14-positive vesicles is unknown
    • Whether other Rab substrates contribute to the metastatic phenotype was not dissected
  3. 2021 Medium

    Showing that CHML binds Rab5A and promotes NSCLC proliferation while being regulated by miR-199a-3p extended CHML's cancer-relevant Rab partnerships beyond Rab14 and identified a post-transcriptional regulatory axis.

    Evidence Co-immunoprecipitation of CHML–Rab5A, siRNA knockdown, xenograft model, and miRNA overexpression/inhibition in NSCLC cells

    PMID:34649053

    Open questions at the time
    • CHML–Rab5A interaction rests on a single co-IP without reciprocal validation or domain mapping
    • Whether the proliferative effect depends on Rab5A prenylation or an escort-independent mechanism is unclear
    • miR-199a-3p regulation not confirmed with endogenous miRNA knockout
  4. 2022 Medium

    Identifying CHML as an NRF2 transcriptional target that mediates mTOR lysosomal recruitment linked Rab escort function to nutrient-sensing signaling and antioxidant response pathways.

    Evidence ARE promoter analysis, siRNA knockdown, overexpression, and mTOR lysosomal localization imaging

    PMID:35184380

    Open questions at the time
    • Which specific Rab substrate(s) mediate mTOR lysosomal translocation downstream of CHML is not identified
    • ChIP-seq confirmation of direct NRF2 occupancy at the CHML promoter in multiple cell types is lacking
    • Whether NRF2–CHML–mTOR axis operates in non-cancer contexts is untested
  5. 2025 Low

    Proposing that CHML upregulates SLC44A3-mediated choline uptake to increase phosphatidic acid production and activate MAPK/PI3K-AKT signaling introduced a metabolic mechanism for CHML-driven HCC invasion, though the pathway lacks direct biochemical validation.

    Evidence CHML knockout/overexpression with integrated transcriptomics and untargeted metabolomics, Transwell and xenograft assays in HCC cells

    PMID:40842592

    Open questions at the time
    • SLC44A3–PA–MAPK/PI3K axis is inferred from omics correlation without direct biochemical validation of causality
    • Whether SLC44A3 upregulation depends on a specific Rab substrate escorted by CHML is unknown
    • Single-lab study with no independent replication or citations

Open questions

Synthesis pass · forward-looking unresolved questions
  • It remains unknown which specific Rab substrates mediate CHML's effects on mTOR lysosomal activation and choline metabolism, and no structural model of REP-2 in complex with any human Rab has been determined.
  • No structural model of REP-2 bound to a Rab substrate or the geranylgeranyltransferase complex
  • Complete inventory of Rab substrates preferentially dependent on REP-2 vs REP-1 in vivo is missing
  • In vivo phenotype of CHML loss in a mammalian genetic model has not been reported

Mechanism profile

Synthesis pass · controlled-vocabulary classification · explore literature graph →
Molecular activity
GO:0060090 molecular adaptor activity 2 GO:0008289 lipid binding 1
Localization
GO:0005764 lysosome 1 GO:0005829 cytosol 1 GO:0031410 cytoplasmic vesicle 1
Pathway
R-HSA-392499 Metabolism of proteins 2 R-HSA-162582 Signal Transduction 1 R-HSA-5653656 Vesicle-mediated transport 1
Partners
RAB14RAB1ARAB3ARAB5ARAB6A

Evidence

Reading pass · 5 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
1994 CHML encodes REP-2 (Rab escort protein 2), which binds newly synthesized Rab proteins and facilitates geranylgeranyl (GG) group attachment by the Rab GG transferase catalytic component; GG transfer is absolutely dependent on REP participation. REP-2 was approximately equal to REP-1 in supporting GG attachment to Rab1A, Rab5A, and Rab6, but only 25% as active toward Rab3A and Rab3D. Replacing the C-terminal 12 amino acids of Rab3A with those of Rab1A restored REP-2 activity to normal, demonstrating substrate specificity is determined by Rab C-terminal sequence. Recombinant protein production, in vitro GG transferase assay, domain-swap mutagenesis The Journal of biological chemistry High 8294464
2019 CHML promotes HCC cell migration, invasion, and metastasis by escorting Rab14 to the membrane, facilitating constant Rab14 recycling. Rab14-positive vesicles carry metastasis regulators Mucin13 and CD44 as cargo, contributing to the pro-metastatic effect. siRNA knockdown, overexpression, in vitro migration/invasion assays, in vivo metastasis model, co-immunoprecipitation, vesicle cargo identification Nature communications High 31175290
2022 CHML/Rep2 is a transcriptional target of NRF2 via an antioxidant response element (ARE) in its promoter (-1622 to -1612). Loss of Rep2 inhibits mTOR translocation and activation at the lysosome, while overexpression enhances it, establishing Rep2 as a mediator of mTOR lysosomal function downstream of NRF2. siRNA knockdown, overexpression, ARE reporter/promoter analysis, mTOR localization imaging at lysosome, cell proliferation assay Molecular oncology Medium 35184380
2021 CHML promotes proliferation and inhibits apoptosis of non-small cell lung cancer cells via direct binding to Rab5A, as demonstrated by co-immunoprecipitation. CHML is regulated upstream by miR-199a-3p, which targets CHML mRNA. siRNA knockdown, xenograft mouse model, co-immunoprecipitation, miRNA overexpression/inhibition Pathology, research and practice Medium 34649053
2025 CHML promotes HCC cell migration and invasion by upregulating SLC44A3 (a choline transporter), increasing choline uptake and phosphatidic acid (PA) production, which in turn activates MAPK and PI3K-AKT signaling cascades. This mechanism was identified through integration of transcriptomics and untargeted metabolomics after CHML knockout or overexpression. CHML knockout/overexpression, transcriptome sequencing, untargeted metabolomics, wound healing, Transwell assay, xenograft model Frontiers in oncology Low 40842592

Source papers

Stage 0 corpus · 10 papers · ranked by NIH iCite citations
Year Title Journal Citations PMID
1994 REP-2, a Rab escort protein encoded by the choroideremia-like gene. The Journal of biological chemistry 159 8294464
2019 CHML promotes liver cancer metastasis by facilitating Rab14 recycle. Nature communications 43 31175290
2003 Identification, cDNA cloning and possible roles of seed-specific rice asparaginyl endopeptidase, REP-2. Planta 20 12684786
1994 Mapping of the choroideremia-like (CHML) gene at 1q42-qter and mutation analysis in patients with Usher syndrome type II. Genomics 15 8188272
2022 CHML is an NRF2 target gene that regulates mTOR function. Molecular oncology 5 35184380
2021 CHML targeted by miR-199a-3p promotes non-small cell lung cancer cell growth via binding to Rab5A. Pathology, research and practice 5 34649053
2023 Bioengineered Hybrid Rep 2/6 Gene Improves Encapsulation of a Single-Stranded Expression Cassette into AAV6 Vectors. Genes 4 37895215
2001 Antitumor activity of cytotropic heterogeneous molecular lipids (CHML) on human breast cancer xenograft in nude mice. Anticancer research 4 11724310
1999 CHML suppresses cell growth and induces apoptosis in multiple human tumor lines. Anticancer research 3 10652570
2025 CHML regulates migration and invasion in hepatocellular carcinoma via transcriptional and metabolic reprogramming. Frontiers in oncology 0 40842592