Affinage

ARL4A

ADP-ribosylation factor-like protein 4A · UniProt P40617

Length
200 aa
Mass
22.6 kDa
Annotated
2026-06-09
9 papers in source corpus 8 papers cited in narrative 8 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

ARL4A is a myristoylated Arf-like small GTPase that functions as a membrane-recruitment hub, converting its membrane association into the localized assembly of signaling and trafficking effectors that drive actin remodeling, cell migration, and Golgi/endosome organization (PMID:17398095, PMID:21930703, PMID:22159419). At the plasma membrane it binds directly to the PH domains of cytohesin Arf-GEFs (ARNO/cytohesin-2 and relatives) to recruit them and activate Arf6 independently of PtdIns(3,4,5)P3 (PMID:17398095), and it engages the Ras-binding domain of ELMO to provide a membrane-localization signal that drives membrane ruffling and stress-fiber disassembly through the ELMO-DOCK180-Rac axis (PMID:21930703). ARL4A also recruits and cooperates with the kinases Pak1/Pak2 at the plasma membrane to sustain Pak1 activation and fibronectin-induced migration, with Pak1 capable of reciprocally recruiting ARL4A (PMID:31932503); Pak1-mediated phosphorylation of ARL4A at S143 promotes binding of the chaperone HYPK, which stabilizes ARL4A against proteasomal degradation, establishing protein stability—rather than the canonical GTPase cycle—as a key regulatory mechanism (PMID:35857868). Beyond the plasma membrane, ARL4A binds the trans-Golgi golgin GCC185 in a GTP-dependent manner and is required for GCC185-mediated recruitment of CLASP1/CLASP2 to maintain Golgi structure and endosome-to-Golgi transport (PMID:22159419), and at endosomes it binds the ESCRT-II subunit VPS36 to stabilize ESCRT-III association and attenuate EGFR degradation (PMID:38030597). ARL4A localizes to nuclei and nucleoli and interacts with importin-alpha through its C-terminal NLS in a nucleotide-independent manner (PMID:10980193), and its genetic disruption in mice reduces testis weight and sperm count, implicating it in germ cell development (PMID:11909968).

Mechanistic history

Synthesis pass · year-by-year structured walk · 7 steps
  1. 2000 Medium

    Established the first localization and interaction features of ARL4A, defining it as a myristoylated GTPase with a nucleotide-independent nuclear import partner and nucleolar targeting.

    Evidence Immunofluorescence, yeast two-hybrid, in vitro binding, and myristoylation assays identifying importin-alpha binding via the C-terminal NLS

    PMID:10980193

    Open questions at the time
    • Functional consequence of nuclear/nucleolar localization not established
    • No effector identified at this stage
    • Nucleotide-state dependence of localization only partially resolved
  2. 2002 Medium

    Provided in vivo evidence that ARL4A contributes to germ cell development, addressing whether the gene has a non-redundant physiological role.

    Evidence Targeted gene disruption in mice with testis histology and sperm counting

    PMID:11909968

    Open questions at the time
    • Molecular mechanism in germ cells not defined
    • Fertility unaffected, so the cellular pathway involved is unclear
    • Possible compensation by Arl4 paralogs not assessed
  3. 2007 High

    Identified the first effector mechanism, showing ARL4A activates Arf6 by recruiting cytohesin GEFs to the membrane, linking it to membrane trafficking/signaling.

    Evidence Membrane recruitment and direct PH-domain binding assays with multiple cytohesins and splice forms

    PMID:17398095

    Open questions at the time
    • Downstream Arf6-dependent cellular outputs not fully mapped
    • Regulation of ARL4A's own membrane recruitment unresolved
  4. 2011 High

    Connected ARL4A to actin cytoskeletal remodeling and to Golgi structural maintenance, broadening its effector repertoire to Rac signaling and trans-Golgi golgins.

    Evidence Interaction screens and binding assays identifying ELMO (RBD binding, ELMO-DOCK180-Rac) and GCC185 (GTP-dependent, CLASP1/2 recruitment), with cytoskeletal and Golgi morphology/transport readouts

    PMID:21930703 PMID:22159419

    Open questions at the time
    • How ARL4A partitions between plasma membrane and Golgi pools is unclear
    • Coordination between ELMO and GCC185 branches not defined
  5. 2020 Medium

    Defined ARL4A as part of a feedback circuit with Pak1/Pak2 driving sustained kinase activation and integrin-stimulated migration.

    Evidence Co-IP, confocal membrane-localization assays, depletion/rescue, and cell migration assays with myristoylation-deficient G2A mutant

    PMID:31932503

    Open questions at the time
    • Mechanism of bidirectional recruitment not structurally resolved
    • Relationship to the Arf6/Rac branches during migration unclear
  6. 2022 High

    Revealed that ARL4A is regulated by phosphorylation-dependent protein stability rather than the canonical GTPase cycle, identifying HYPK chaperone-mediated stabilization downstream of Pak1.

    Evidence Phosphoproteomics, kinase validation by siRNA/rescue, Co-IP, proteasome inhibition, and migration assays identifying S143 phosphorylation and HYPK binding

    PMID:35857868

    Open questions at the time
    • How HYPK binding mechanistically blocks degradation not defined
    • Interplay between nucleotide loading and stability regulation unresolved
  7. 2023 High

    Established an endosomal function for ARL4A in regulating receptor degradation, showing it tunes EGFR turnover via ESCRT machinery.

    Evidence Direct binding, Co-IP, EGFR ubiquitinylation/degradation assays, and interaction-defective mutants dissecting VPS36-ESCRT-III and USP8/CHMP2A links

    PMID:38030597

    Open questions at the time
    • Physiological signaling consequences of prolonged EGFR signaling not mapped
    • How ARL4A is targeted to endosomes vs plasma membrane unclear

Open questions

Synthesis pass · forward-looking unresolved questions
  • How ARL4A coordinates its multiple effector branches and subcellular pools (plasma membrane, Golgi, endosome, nucleus) into a unified cellular program remains unresolved.
  • No structural model integrating the distinct effector interactions
  • Mechanism controlling distribution among subcellular compartments unknown
  • Physiological relevance of the nucleolar pool uncharacterized

Mechanism profile

Synthesis pass · controlled-vocabulary classification · explore literature graph →
Molecular activity
GO:0060090 molecular adaptor activity 4 GO:0098772 molecular function regulator activity 2 GO:0003924 GTPase activity 1
Localization
GO:0005886 plasma membrane 3 GO:0005634 nucleus 1 GO:0005730 nucleolus 1 GO:0005768 endosome 1 GO:0005794 Golgi apparatus 1
Pathway
R-HSA-162582 Signal Transduction 3 R-HSA-5653656 Vesicle-mediated transport 2
Partners
CYTH2DOCK180ELMO1GCC185HYPKKPNAPAK1VPS36

Evidence

Reading pass · 8 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
2007 Arl4A (along with Arl4c and Arl4d) recruits the cytohesin Arf-GEFs (ARNO/cytohesin-2 and relatives) to the plasma membrane by binding directly to their PH domains, irrespective of the diglycine or triglycine splice form, thereby activating Arf6 independently of PtdIns(3,4,5)P3 generation. Membrane recruitment assays, direct binding to PH domains demonstrated in cell-based and biochemical assays Current biology : CB High 17398095
2000 ARL4A localizes predominantly to nuclei and nucleoli; the GDP-bound T34N mutant concentrates in nucleoli. ARL4A interacts with importin-alpha through its C-terminal NLS region in a nucleotide-independent manner. Its N-terminus is myristoylated. Immunofluorescence microscopy, yeast two-hybrid screening, in vitro protein-interaction assays, myristoylation assay The Journal of biological chemistry Medium 10980193
2002 Targeted disruption of the Arl4 gene in mice results in a 30% reduction in testis weight and 60% reduction in sperm count without affecting fertility, suggesting a role for Arl4A in germ cell development, possibly at meiosis. Targeted gene disruption (knockout mouse), histology, sperm counting Molecular and cellular biology Medium 11909968
2011 Arl4A binds the Ras-binding domain (RBD) of ELMO proteins and acts as a membrane localization signal for ELMO; membrane targeting of ELMO via Arl4A promotes cytoskeletal reorganization (membrane ruffling and stress fiber disassembly) through an ELMO-DOCK180-Rac signaling pathway. Two independent interaction screens (active GTPase library, brain cDNA library), binding assays, cell-based cytoskeletal readouts The Journal of biological chemistry High 21930703
2011 ARL4A directly interacts with the trans-Golgi network golgin GCC185 in a GTP-dependent manner via the CC2 domain of GCC185. Depletion of ARL4A causes Golgi fragmentation and defects in endosome-to-Golgi transport, phenocopying GCC185 depletion. ARL4A is required for GCC185-mediated Golgi recruitment of CLASP1 and CLASP2. Co-immunoprecipitation, direct binding assays, siRNA depletion with Golgi morphology and transport readouts, in vivo interaction assays Journal of cell science High 22159419
2020 Arl4A interacts with Pak1 and Pak2, recruits them to the plasma membrane, and their cooperative membrane recruitment is required for sustained Pak1 activation and fibronectin-induced cell migration. Pak1 can also recruit myristoylation-deficient Arl4A-G2A to the plasma membrane, indicating bidirectional feedback recruitment. Co-immunoprecipitation, confocal microscopy with plasma membrane localization assays, Arl4A depletion and rescue experiments, cell migration assays Journal of cell science Medium 31932503
2022 Fibronectin stimulation induces Pak1-mediated phosphorylation of Arl4A at S143 (and Arl4D at S144), which promotes binding of the chaperone HYPK to Arl4A/D, stabilizing them against proteasomal degradation and enabling their stable recruitment to the plasma membrane to promote cell migration. Protein stability, not the GTPase cycle, is thus a key regulatory mechanism for Arl4A. Proteomic/phosphoproteomic analysis, kinase identification by siRNA/rescue, co-immunoprecipitation, proteasome inhibition assays, cell migration assays Proceedings of the National Academy of Sciences of the United States of America High 35857868
2023 Endosomal Arl4A directly binds the ESCRT-II component VPS36, stabilizing VPS36-ESCRT-III association and impairing recruitment of the deubiquitinating enzyme USP8 by CHMP2A, thereby prolonging EGFR ubiquitinylation and attenuating EGFR transport from endosomes to lysosomes for degradation. Direct binding assays, co-immunoprecipitation, EGFR degradation/ubiquitinylation assays, ESCRT complex interaction experiments, loss-of-function and interaction-defective mutant studies Nature communications High 38030597

Source papers

Stage 0 corpus · 9 papers · ranked by NIH iCite citations
Year Title Journal Citations PMID
2007 The Arl4 family of small G proteins can recruit the cytohesin Arf6 exchange factors to the plasma membrane. Current biology : CB 106 17398095
2002 Reduced sperm count and normal fertility in male mice with targeted disruption of the ADP-ribosylation factor-like 4 (Arl4) gene. Molecular and cellular biology 50 11909968
2000 ARL4, an ARF-like protein that is developmentally regulated and localized to nuclei and nucleoli. The Journal of biological chemistry 44 10980193
2011 The Arf family GTPase Arl4A complexes with ELMO proteins to promote actin cytoskeleton remodeling and reveals a versatile Ras-binding domain in the ELMO proteins family. The Journal of biological chemistry 42 21930703
2011 ARL4A acts with GCC185 to modulate Golgi complex organization. Journal of cell science 32 22159419
2022 Phosphorylation of Arl4A/D promotes their binding by the HYPK chaperone for their stable recruitment to the plasma membrane. Proceedings of the National Academy of Sciences of the United States of America 12 35857868
2020 Cooperative recruitment of Arl4A and Pak1 to the plasma membrane contributes to sustained Pak1 activation for cell migration. Journal of cell science 12 31932503
2023 Endosomal Arl4A attenuates EGFR degradation by binding to the ESCRT-II component VPS36. Nature communications 5 38030597
2026 Pan-cancer investigation identifies ARL4A as a prospective therapeutic indicator for thyroid cancer. Discover oncology 0 42118373

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