ARPC2

ARPC2 is a core structural subunit of the heptameric Arp2/3 complex that, together with ARPC4, forms the central scaffold of the complex through long C-terminal α-helices and is essential for branched actin filament nucleation, cell migration, endocytosis, and metastasis (PMID:9230079, PMID:11721045, PMID:18381280, PMID:30710516). The Arp2/3 complex containing ARPC2 is recruited to sites of actin remodeling through direct interactions with cortactin, vinculin, and E-cadherin, coupling actin polymerization to lamellipodial protrusion, focal adhesion dynamics, and cell–cell adhesion (PMID:11018051, PMID:12473693, PMID:11882288). Small-molecule inhibitors benproperine and pimozide bind directly to ARPC2 at a pocket defined by residues F225, F247, and Y250, suppressing actin nucleation, lamellipodium formation, and tumor metastasis in vivo (PMID:30710516, PMID:31571309, PMID:36558913). ARPC2 also functions independently of the full Arp2/3 complex to promote TGF-β1–induced MRTFA nuclear translocation and fibrotic gene expression in lung fibroblasts (PMID:41898590).

1. 1997 High

   Identification of ARPC2 as a subunit of the Arp2/3 complex and its localization to lamellipodia established its role in dynamic actin assembly at the cell periphery, answering the question of which proteins compose the mammalian Arp2/3 complex.

   Evidence Protein purification, sequencing, and immunofluorescence microscopy in human fibroblasts and Listeria actin tails

   PMID:9230079

   Open questions at the time

   • No structural information on how ARPC2 integrates into the complex
   • Functional requirement for ARPC2 in actin nucleation not yet tested
2. 2000 High

   Demonstration that cortactin directly interacts with the Arp2/3 complex and that this interaction is required for peripheral actin assembly revealed a key upstream recruitment mechanism for ARPC2-containing complexes.

   Evidence Affinity chromatography and immunoprecipitation with purified proteins, deletion mutagenesis, and immunofluorescence in fibroblasts

   PMID:11018051

   Open questions at the time

   • Specific ARPC2 contacts within the cortactin–Arp2/3 interface not mapped
   • Functional consequences of disrupting cortactin–Arp2/3 binding on actin nucleation kinetics not measured
3. 2001 High

   The 2.0 Å crystal structure of the Arp2/3 complex resolved ARPC2 and ARPC4 as the central structural scaffold, answering how the seven subunits are architecturally organized and establishing ARPC2's core role.

   Evidence X-ray crystallography of the bovine Arp2/3 complex

   PMID:11721045

   Open questions at the time

   • Structure captured in the inactive conformation; how ARPC2 rearranges upon activation was unresolved
   • No mutational validation of predicted subunit contacts in this study
4. 2002 High

   Physical associations of the Arp2/3 complex with vinculin and E-cadherin demonstrated that ARPC2-containing complexes are recruited to both integrin-based adhesions and cadherin-based cell–cell contacts, broadening its functional scope beyond lamellipodia.

   Evidence Co-immunoprecipitation, direct binding assays with purified proteins, mutagenesis of vinculin, and E-cadherin ligation assays

   PMID:11882288 PMID:12473693

   Open questions at the time

   • Whether ARPC2 itself directly contacts vinculin or E-cadherin was not distinguished from contacts through other subunits
5. 2004 High

   Mutagenesis of yeast ARPC2 (arc35) defined three functionally separable surfaces—for actin nucleation, ARPC4 contact, and endocytosis—establishing that ARPC2 has distinct, non-overlapping roles in Arp2/3 complex functions.

   Evidence Integrated yeast mutant alleles, purification of mutant Arp2/3 complexes, in vitro actin assembly with WASp, and in vivo endocytosis assays

   PMID:18381280

   Open questions at the time

   • Whether mammalian ARPC2 retains identical functional surfaces was not tested
   • Structural basis of the endocytosis-specific surface unresolved
6. 2015 Medium

   Discovery that ARPC2 binds microtubules in addition to actin, with mapping of a microtubule-binding domain, revealed an unexpected cytoskeletal crosstalk function.

   Evidence In vitro co-sedimentation with truncated ARPC2, GFP-ARPC2 live imaging in plant cells, pharmacological validation

   PMID:26706062

   Open questions at the time

   • Demonstrated in plant orthologs; confirmation of microtubule binding for mammalian ARPC2 not shown
   • Physiological consequence of microtubule binding unclear
7. 2019 High

   Identification of benproperine and pimozide as direct ARPC2-binding inhibitors, with mutagenesis defining a drug-binding pocket at F225/F247/Y250, provided both pharmacological tools and a druggable surface on ARPC2 for anti-metastasis therapy.

   Evidence DARTS, CETSA, SPR, site-directed mutagenesis, actin polymerization assays, and in vivo metastasis models

   PMID:30710516 PMID:31571309 PMID:36558913

   Open questions at the time

   • Co-crystal structure of drug–ARPC2 complex not available
   • Selectivity for ARPC2 over other Arp2/3 subunits in vivo not fully characterized
8. 2019 Medium

   ARPC2 mRNA was found to contain an IRES element with a G-quadruplex motif enabling cap-independent translation under stress, and RBM3 was shown to post-transcriptionally regulate ARPC2 protein levels via its 3ʹ-UTR, revealing multi-layered translational control of ARPC2 expression.

   Evidence Bicistronic reporters, RNA structural probing, RBM3 knockdown with 3ʹ-UTR binding analysis

   PMID:30720048 PMID:31387452

   Open questions at the time

   • In vivo relevance of IRES-mediated ARPC2 translation not tested
   • RBM3–ARPC2 axis validated only in breast cancer cells
9. 2023 Medium

   Pharmacological ARPC2 inhibition disrupted intestinal stem cell homeostasis and activated YAP signaling, demonstrating that Arp2/3-dependent actin dynamics are required for ISC maintenance and Paneth cell differentiation.

   Evidence Benproperine treatment in vivo and in intestinal organoids, BrdU/EdU incorporation, IHC, flow cytometry

   PMID:37849945

   Open questions at the time

   • Genetic ARPC2 deletion in ISCs not performed
   • Whether YAP activation is a direct or indirect consequence of actin disruption not resolved
10. 2025 Medium

    ARPC2 was shown to promote TGF-β1–induced MRTFA nuclear translocation and fibrotic gene expression independently of other Arp2/3 subunits, establishing a non-canonical, complex-independent function for ARPC2 in fibroblast-to-myofibroblast transition.

    Evidence ARPC2 overexpression and knockdown with separate ACTR2 depletion, nuclear/cytoplasmic fractionation, transcriptomics in MRC-5 fibroblasts

    PMID:41898590

    Open questions at the time

    • Mechanism by which ARPC2 alone modulates G-actin/MRTFA not defined
    • In vivo relevance in fibrotic disease models not tested
    • Single-lab finding requires independent replication

• Key open questions include the structural basis of drug binding to ARPC2, whether ARPC2's complex-independent MRTFA regulation occurs in vivo, and whether ARPC2's microtubule-binding activity is conserved and functionally relevant in mammalian cells.
• No co-crystal structure of any small molecule bound to ARPC2
• Complex-independent ARPC2 functions demonstrated only in cultured fibroblasts
• Microtubule binding shown only for plant orthologs