id: MODULE:glut4_insulin_stimulated_glucose_uptake title: Insulin-stimulated GLUT4 glucose uptake — AKT2 inhibition of the TBC1D4/TBC1D1 Rab GAPs, RAB10 or RAB8A/RAB13 activation, motor-driven GLUT4 storage vesicle movement, cortical actin remodelling, STX4-SNAP23-VAMP2 fusion and SLC2A4 glucose transport; AKT2/TBC1D4/TBC1D1/RAB10/DENND4C/RAB8A/RAB13/KIF5B/MYO5A/MYO1C/RAC1/PAK1/STX4/SNAP23/VAMP2/STXBP3/STXBP4/SLC2A4 description: >- In fat cells and in skeletal and cardiac muscle, insulin raises glucose uptake by moving the facilitative glucose transporter GLUT4 (SLC2A4) from intracellular stores to the cell surface. In the unstimulated cell most GLUT4 sits in small GLUT4 storage vesicles (GSVs, the insulin-responsive compartment) that are retained inside the cell. Insulin receptor signalling through IRS proteins and class I PI3K activates the kinase AKT2. AKT2 phosphorylates the Rab GTPase-activating proteins TBC1D4 (AS160) and its paralogue TBC1D1, which suppresses their GAP activity toward GSV Rabs. The GTP-bound Rab that results is RAB10 in adipocytes, loaded by the exchange factor DENND4C, and RAB8A and RAB13 in muscle cells. Active Rabs, together with kinesin-1 (KIF5B) on microtubules and the myosins MYO5A (itself an AKT2 substrate) and MYO1C on cortical actin, carry GSVs to the cell periphery. In muscle, insulin also activates RAC1, which through PAK1 and the ARP2/3 complex remodels the cortical actin meshwork beneath the plasma membrane, a cycle of actin branching and cofilin-mediated severing that is needed for GLUT4 to reach the surface. GSVs then fuse with the plasma membrane through a SNARE complex of the vesicle SNARE VAMP2 with the plasma membrane SNAREs syntaxin-4 (STX4) and SNAP23, regulated by the syntaxin-4-binding proteins Munc18c (STXBP3) and Synip (STXBP4); AKT2 phosphorylation of Synip releases it from syntaxin-4. GLUT4 inserted into the plasma membrane then transports D-glucose down its gradient into the cell. Defects at several of these steps (AKT2 mutations, truncating TBC1D4 variants, reduced syntaxin-4) cause insulin resistance. status: DRAFT scope: CONCRETE evidence: - source_id: PW:0000639 title: insulin responsive facilitative sugar transporter mediated glucose transport pathway statement: >- The module boundary follows the RGD Pathway Ontology term and its diagram. The diagram draws Akt2 negatively affecting Tbc1d4 and Stxbp4; Tbc1d4 negatively affecting its Rab targets, which positively affect Rabs at GSVs; Lnpep associated with Tbc1d4; Stx4 associated with and inhibited by Stxbp4; Limk1 negatively affecting Cfl1; Cfl1 and the Arp2/3 complex positively affecting actin cycling; Rac1 positively affecting Rac1 effectors; and Rhoq, Trip10, Gapvd1 and Rab31 as a negative-regulator branch acting on Slc2a4. The record text adds the GSV Rabs (Rab2a, 4a, 5a, 8a, 10, 11a, 13, 14), their GEFs (Dennd4 proteins, Rab3ip, Dennd1c), the kinesins and myosins, the Rac1 GEFs, and the Vamp2-Stx4-Snap23 fusion complex with Stxbp3. Derived through projects/RGD_PATHWAY_ONTOLOGY (pathways/PW_0000639.yaml). - source_id: GO:0044381 title: glucose import in response to insulin stimulus statement: >- The GO mapping recorded for PW:0000639 in the project's module seeds (skos:closeMatch, curated). It is the module's process concept. - source_id: gomodel:63d320cd00001536 title: FBXL19-mediated degradation of RAC1 (Human) statement: >- The project's best-overlap GO-CAM for PW:0000639 (overlap 2 genes, AKT1 and RAC1). It models AKT1 phosphorylation of RAC1 leading to FBXL19-mediated RAC1 degradation in cell migration and does not concern glucose uptake. Only its RAC1 GTPase activity node matches an annoton here (gene and MF), and that link is recorded on the RAC1 annoton. - source_id: gomodel:613aae0000000885 title: PTPRM role in glucose transport activity through inhibition of CTNND1 (Human) statement: >- Human GO-CAM in which SLC2A4 enables D-glucose transmembrane transporter activity (GO:0055056) in the plasma membrane, part of D-glucose transmembrane transport, positively regulated by the palmitoyltransferase ZDHHC7. The SLC2A4 node is linked to the transporter annoton. - source_id: PMID:12637568 title: Insulin-stimulated phosphorylation of a Rab GTPase-activating protein regulates GLUT4 translocation. statement: >- AKT phosphorylation of AS160 (TBC1D4) inactivates its Rab GAP function, the switch that couples insulin signalling to GLUT4 translocation. supporting_text: These findings strongly indicate that insulin-stimulated phosphorylation of AS160 is required for GLUT4 translocation and that this phosphorylation signals translocation through inactivation of the Rab GAP function. - source_id: PMID:21454697 title: Insulin-stimulated GLUT4 protein translocation in adipocytes requires the Rab10 guanine nucleotide exchange factor Dennd4C. statement: The adipocyte pathway in outline, from TBC1D4 phosphorylation to GLUT4 vesicle fusion. supporting_text: Insulin-elicited phosphorylation of the GTPase-activating protein TBC1D4 (AS160) suppresses its activity toward Rab10 and thereby leads to an increase in the GTP-bound form of Rab10, which in turn triggers movement of vesicles containing GLUT4 to the plasma membrane and their fusion with the membrane. - source_id: PMID:15494023 title: Analysis of insulin signalling by RNAi-based gene silencing. statement: >- siRNA screen in adipocytes: AKT2, not AKT1, is the AKT isoform that carries the signal to GLUT4, and depletion of the CAP, CrkII and Cbl components of the TC10 arm did not reduce insulin signalling to GLUT4 (boundary decisions 1 and 4). supporting_text: These results show that Akt2/PKBbeta is the key downstream intermediate within the phosphoinositide 3-kinase pathway linked to insulin action on GLUT4 in cultured adipocytes - source_id: PMID:11309621 title: Insulin-stimulated GLUT4 translocation requires the CAP-dependent activation of TC10. statement: >- The original description of the PI3K-independent CAP-Cbl-CrkII-C3G-TC10 arm, recorded as context and as a knowledge gap rather than as a part (boundary decision 4). supporting_text: The TC10 pathway functions in parallel with PI(3)K to stimulate fully GLUT4 translocation in response to insulin. - source_id: PMID:20410133 title: Insulin-regulated aminopeptidase is a key regulator of GLUT4 trafficking by controlling the sorting of GLUT4 from endosomes to specialized insulin-regulated vesicles. statement: >- IRAP (LNPEP) is GSV cargo that also sorts GLUT4 into GSVs in the basal state; it does not recruit AS160 to GSVs. Recorded as context, not as a part (boundary decision 3). supporting_text: In sum, we show that IRAP is both cargo and a key regulator of the insulin-regulated pathway. notes: >- Derived from RGD PW:0000639 through the RGD_PATHWAY_ONTOLOGY project's diagram->module route. RGD curates 54 human genes. Modelled here (18): AKT2, TBC1D4, TBC1D1, RAB10, DENND4C, RAB8A, RAB13, KIF5B, MYO5A, MYO1C, RAC1, PAK1, the ARP2/3 complex (one family descriptor with ACTR2, ACTR3 and ARPC2 as representatives), STX4, SNAP23, VAMP2, STXBP3, STXBP4 and SLC2A4. The IR-IRS-PI3K-AKT steps are included by reference to insulin_receptor_signaling#akt_foxo_output, the AKT step of that module (PW:0000143 and PW:0000232 are mentioned here but not listed as evidence, since this module does not cover them). Molecular functions come from QuickGO experimental rows (October 2026) where they exist: SLC2A4 GO:0055056 (IDA), AKT2 and PAK1 GO:0004674 (IDA), RAB10, RAB8A, RAB13 and RAC1 GTPase activity GO:0003924 (IDA/EXP; core in the RAB8A review), DENND4C GO:0005085 (IDA), KIF5B GO:0008574 and MYO5A GO:0000146 (core in their reviews), ACTR2/ACTR3 GO:0005200 (IDA; core in the ARPC1B/ARPC4/ARPC5 reviews), SNAP23 GO:0005484 (IDA; core in the SNAP23 review), STXBP3 and STXBP4 syntaxin binding GO:0019905 (IPI). TBC1D4 and TBC1D1 GTPase activator activity GO:0005096, STX4 and VAMP2 GO:0005484 and MYO1C GO:0000146 rest on IBA rows plus the cited biochemistry, because no experimental MF row exists in human GOA. Comparator check (CLAUDE.md). QuickGO annotations to GO:0044381 in human, mouse and rat are carried only by SLC2A4, TRARG1, ZDHHC7, SLC27A1, SLC27A4 and SGCB. None of the trafficking machinery (TBC1D4, Rabs, motors, SNAREs) carries it; GO:0044381 is_a D-glucose import across plasma membrane, so it describes the transport event, which SLC2A4 performs. The term is therefore the module concept and is attached only to the SLC2A4 annoton; the other annotons carry functions, not this process. TRARG1 and ZDHHC7 (GLUT4 palmitoylation) are not on the RGD list and are left for a later revision. Boundary decisions. (1) AKT1 is excluded: AKT2 is the isoform required (PMID:15494023), and AKT2 has a direct annoton here with TBC1D4, TBC1D1, MYO5A and STXBP4 as substrates. (2) Of the eight GSV Rabs in the RGD text, RAB10 (adipocyte) and RAB8A/RAB13 (muscle) are modelled because they are the AS160 targets shown to be required for GLUT4 translocation (PMID:17403373, PMID:21041651); RAB2A and RAB14 are AS160 substrates in vitro (PMID:15971998) and RAB4A, RAB5A, RAB8B and RAB11A act in GLUT4 endosomal recycling, so they are context. DENND4C is modelled as the RAB10 GEF; DENND4A, DENND4B, RAB3IP (Rabin8) and DENND1C are other Rab GEFs named by RGD without GLUT4-specific loss-of-function data here. (3) LNPEP (IRAP) is excluded by the substrate-vs-participant rule: it is GSV cargo that co-translocates with GLUT4, and its aminopeptidase activity performs no step of insulin-stimulated glucose import; its cytoplasmic-tail role sorts GLUT4 into GSVs in the basal state (GSV biogenesis and retention), and it does not recruit AS160 (PMID:20410133). (4) The CAP (SORBS1)-CBL-CRK-RAPGEF1 (C3G)-RHOQ (TC10) arm is not a part. It was reported as a PI3K-independent requirement (PMID:11309621 but a later siRNA screen found depletion of CAP, CrkII and Cbl did not diminish insulin signalling to GLUT4 (PMID:15494023), so the arm is contested; it is recorded here and as a BIOLOGY knowledge gap. (5) The RHOQ-TRIP10-GAPVD1-RAB31 negative-regulator branch on the RGD diagram belongs to that same contested arm and is left out. (6) Cofilin (CFL1), LIMK1 and SSH1 tune actin dynamics downstream of RAC1/ARP2/3; the actin-remodelling part names RAC1, PAK1 and the ARP2/3 complex (the nucleator), with cofilin cycling described in prose. Other RGD genes not modelled: ARPC1A-5 and the remaining ACTR subunits are folded into the ARP2/3 family descriptor; BAIAP2, CYFIP1, IQGAP1, PREX1, PLEKHG4 and TIAM1 are RAC1 effectors/GEFs recorded as context; KIF3A is a second kinesin; MYO5B is a recycling myosin; SNAP23's partners are modelled, STXBP4 and STXBP3 included. (7) The fusion part follows the well-established STX4-SNAP23-VAMP2 SNARE with Munc18c (STXBP3) and Synip (STXBP4) regulation (PMID:10394363, PMID:11375421, PMID:15690082); AKT2 phosphorylation of Synip (STXBP4) on Ser99 releases it from syntaxin-4 (PMID:17336927). GO-CAM / GOA observations for upstream review. No single GO-CAM models insulin-stimulated GLUT4 translocation end to end; the project's best_gocam (gomodel:63d320cd00001536) is a RAC1 degradation model unrelated to glucose uptake, matching only on the RAC1 GTPase-activity node. TBC1D4, TBC1D1, STX4, VAMP2 and MYO1C lack experimental molecular-function rows in human GOA despite strong functional literature; these functions here rest on IBA plus the cited biochemistry. STXBP4 and STX4's only informative MF is syntaxin/SNAP-receptor binding. module: id: glut4_insulin_stimulated_glucose_uptake label: Insulin-stimulated GLUT4 glucose uptake module_type: SIGNALING_PATHWAY concepts: - preferred_term: glucose import in response to insulin stimulus term: id: GO:0044381 label: glucose import in response to insulin stimulus description: >- The directed movement of glucose into fat or muscle cells triggered by insulin, achieved by translocating GLUT4 (SLC2A4) to the plasma membrane. This is the GO term mapped to PW:0000639. context: taxa: - preferred_term: Homo sapiens term: id: NCBITaxon:9606 label: Homo sapiens cellular_components: - preferred_term: insulin-responsive compartment (GLUT4 storage vesicle) term: id: GO:0032593 label: insulin-responsive compartment - preferred_term: plasma membrane term: id: GO:0005886 label: plasma membrane - preferred_term: cytosol term: id: GO:0005829 label: cytosol parts: - order: 1 role: Upstream insulin receptor, PI3K and AKT2 activation node: id: insulin_akt2_activation label: AKT2 activation downstream of the insulin receptor and PI3K (by reference) description: >- Insulin binding to the insulin receptor, IRS phosphorylation, class I PI3K recruitment and AKT activation, included by reference to the AKT output step of the insulin receptor signaling module. In this pathway the required AKT isoform is AKT2 (PMID:15494023); its targets relevant here (TBC1D4, TBC1D1, Synip/STXBP4, MYO5A) are modelled in the steps below. module_ref: insulin_receptor_signaling#akt_foxo_output evidence: - source_id: PMID:15494023 statement: AKT2, not AKT1, is the PI3K-pathway intermediate that signals to GLUT4 in adipocytes. supporting_text: loss of Akt2/PKBbeta significantly attenuated GLUT4 regulation by insulin - order: 2 role: AKT2 phosphorylation of the RabGAPs TBC1D4/TBC1D1 relieving GSV Rabs node: id: rabgap_rab_activation label: AKT2 inactivation of TBC1D4/TBC1D1 and activation of RAB10 or RAB8A/RAB13 module_type: REGULATORY_STEP description: >- AKT2 phosphorylates the Rab GTPase-activating proteins TBC1D4 (AS160) and TBC1D1, suppressing their GAP activity toward GSV Rabs. The de-repressed Rab is loaded with GTP and triggers GLUT4 vesicle movement. Which Rab depends on cell type: RAB10 in adipocytes (GEF DENND4C) and RAB8A with RAB13 in muscle. annotons: - id: akt2_kinase label: AKT2 protein serine/threonine kinase activity participant: selector_type: GENE_PRODUCT gene_product: preferred_term: AKT2 term: id: UniProtKB:P31751 label: RAC-beta serine/threonine-protein kinase function: preferred_term: protein serine/threonine kinase activity term: id: GO:0004674 label: protein serine/threonine kinase activity targets: - preferred_term: TBC1D4 (AS160) term: id: UniProtKB:O60343 label: TBC1 domain family member 4 - preferred_term: TBC1D1 term: id: UniProtKB:Q86TI0 label: TBC1 domain family member 1 - preferred_term: STXBP4 (Synip) term: id: UniProtKB:Q6ZWJ1 label: Syntaxin-binding protein 4 - preferred_term: MYO5A term: id: UniProtKB:Q9Y4I1 label: Unconventional myosin-Va locations: - preferred_term: cytosol term: id: GO:0005829 label: cytosol role_description: >- The insulin-activated AKT isoform required for GLUT4 translocation; phosphorylates the RabGAPs and Synip to drive and de-repress the trafficking machinery. evidence: - source_id: PMID:12637568 statement: AKT phosphorylation of AS160 (TBC1D4) is required for GLUT4 translocation and works by inactivating its Rab GAP function. supporting_text: insulin-stimulated phosphorylation of AS160 is required for GLUT4 translocation and that this phosphorylation signals translocation through inactivation of the Rab GAP function - id: tbc1d4_gap label: TBC1D4 (AS160) Rab GTPase-activating protein activity participant: selector_type: GENE_PRODUCT gene_product: preferred_term: TBC1D4 term: id: UniProtKB:O60343 label: TBC1 domain family member 4 function: preferred_term: GTPase activator activity term: id: GO:0005096 label: GTPase activator activity targets: - preferred_term: RAB10 term: id: UniProtKB:P61026 label: Ras-related protein Rab-10 - preferred_term: RAB8A term: id: UniProtKB:P61006 label: Ras-related protein Rab-8A locations: - preferred_term: cytosol term: id: GO:0005829 label: cytosol role_description: >- Rab GAP whose AKT2 phosphorylation switches off its activity toward GSV Rabs; the brake on basal GLUT4 retention. Its GAP domain is active against Rabs 2A, 8A, 10 and 14. evidence: - source_id: PMID:15971998 statement: The AS160 GAP domain is active against Rab2A, Rab8A, Rab10 and Rab14, which are present in GLUT4 vesicles. supporting_text: The GAP domain was active against Rabs 2A, 8A, 10 and 14. - id: tbc1d1_gap label: TBC1D1 Rab GTPase-activating protein activity participant: selector_type: GENE_PRODUCT gene_product: preferred_term: TBC1D1 term: id: UniProtKB:Q86TI0 label: TBC1 domain family member 1 function: preferred_term: GTPase activator activity term: id: GO:0005096 label: GTPase activator activity locations: - preferred_term: cytosol term: id: GO:0005829 label: cytosol role_description: >- TBC1D4 paralogue with the same Rab specificity; the predominant RabGAP in skeletal muscle, also an Akt substrate. Its R125W variant affects obesity susceptibility. evidence: - source_id: PMID:17274760 statement: TBC1D1 has the same Rab specificity as AS160, is phosphorylated by insulin on a conserved Akt site, and its GAP activity controls GLUT4 translocation. supporting_text: the Rab specificity of the Tbc1d1 GAP domain is identical with that of AS160 - id: dennd4c_gef label: DENND4C RAB10 guanine nucleotide exchange factor activity participant: selector_type: GENE_PRODUCT gene_product: preferred_term: DENND4C term: id: UniProtKB:Q5VZ89 label: DENN domain-containing protein 4C function: preferred_term: guanyl-nucleotide exchange factor activity term: id: GO:0005085 label: guanyl-nucleotide exchange factor activity targets: - preferred_term: RAB10 term: id: UniProtKB:P61026 label: Ras-related protein Rab-10 locations: - preferred_term: insulin-responsive compartment (GLUT4 storage vesicle) term: id: GO:0032593 label: insulin-responsive compartment role_description: >- The RAB10 GEF required for GLUT4 translocation in adipocytes; loads RAB10 with GTP once TBC1D4 is switched off. Found on isolated GLUT4 vesicles. evidence: - source_id: PMID:21454697 statement: Dennd4C is the primary RAB10 GEF required for GLUT4 translocation in adipocytes. supporting_text: The present study identifies Dennd4C, a recently described GEF for Rab10, as the primary GEF required for GLUT4 translocation. variant_sets: - id: gsv_rab label: GSV Rab activated downstream of the RabGAPs axis: cell type selection: ONE_OR_MORE notes: >- RAB10 is the required AS160 target in adipocytes; RAB8A and RAB13 are the required targets in muscle cells (RAB8A acting before RAB13). All are closely related Rab8 subfamily GTPases and AS160/TBC1D1 GAP substrates. variants: - id: rab10_adipocyte label: RAB10 (adipocyte) module_type: REGULATORY_STEP annotons: - id: rab10_gtpase label: RAB10 GTPase activity participant: selector_type: GENE_PRODUCT gene_product: preferred_term: RAB10 term: id: UniProtKB:P61026 label: Ras-related protein Rab-10 function: preferred_term: GTPase activity term: id: GO:0003924 label: GTPase activity locations: - preferred_term: insulin-responsive compartment (GLUT4 storage vesicle) term: id: GO:0032593 label: insulin-responsive compartment role_description: >- The GTP-loaded GSV Rab that triggers GLUT4 vesicle movement and fusion in adipocytes; downstream target of AS160. evidence: - source_id: PMID:17403373 statement: Rab10 is a downstream target of AS160 required for insulin-stimulated GLUT4 translocation in adipocytes. supporting_text: Rab10 functions as a downstream target of AS160 in the insulin-signaling pathway that regulates GLUT4 translocation in adipocytes - id: rab8a_rab13_muscle label: RAB8A and RAB13 (muscle) module_type: REGULATORY_STEP annotons: - id: rab8a_gtpase label: RAB8A GTPase activity participant: selector_type: GENE_PRODUCT gene_product: preferred_term: RAB8A term: id: UniProtKB:P61006 label: Ras-related protein Rab-8A function: preferred_term: GTPase activity term: id: GO:0003924 label: GTPase activity locations: - preferred_term: cytosol term: id: GO:0005829 label: cytosol role_description: Insulin-activated GSV Rab in muscle, acting before RAB13. evidence: - source_id: PMID:21041651 statement: Insulin activates Rab8A (and Rab13) and both regulate GLUT4 translocation in muscle cells, downstream of AS160. supporting_text: insulin promotes GTP loading of Rab13 and Rab8A but not Rab10 in rat L6 muscle cells, Rab8A activation preceding that of Rab13 - id: rab13_gtpase label: RAB13 GTPase activity participant: selector_type: GENE_PRODUCT gene_product: preferred_term: RAB13 term: id: UniProtKB:P51153 label: Ras-related protein Rab-13 function: preferred_term: GTPase activity term: id: GO:0003924 label: GTPase activity locations: - preferred_term: cell periphery term: id: GO:0071944 label: cell periphery role_description: >- Insulin-activated GSV Rab in muscle; its knockdown blocks the insulin-induced increase of surface GLUT4, rescued by RAB13 but not RAB8A. evidence: - source_id: PMID:21041651 statement: Rab13 knockdown blocks the insulin-induced increase of surface GLUT4 in muscle cells. supporting_text: siRNA-mediated Rab13 knockdown blocked the insulin-induced increase of GLUT4 at the muscle cell surface that was rescued by a Rab13 ortholog but not by Rab8A - order: 3 role: GLUT4 storage-vesicle movement along microtubules and actin node: id: gsv_movement label: Motor-driven GLUT4 storage vesicle movement (KIF5B, MYO5A, MYO1C) module_type: REGULATORY_STEP description: >- GTP-loaded GSV Rabs recruit cytoskeletal motors that carry GLUT4 vesicles to the cell periphery: the kinesin-1 heavy chain KIF5B moves them along microtubules, while the myosins MYO5A (an AKT2 substrate) and MYO1C move them on cortical actin. All three act in a PI3K-pathway-coupled but, for KIF5B and MYO1C, wortmannin-insensitive manner. annotons: - id: kif5b_motor label: KIF5B microtubule motor activity participant: selector_type: GENE_PRODUCT gene_product: preferred_term: KIF5B term: id: UniProtKB:P33176 label: Kinesin-1 heavy chain function: preferred_term: plus-end-directed microtubule motor activity term: id: GO:0008574 label: plus-end-directed microtubule motor activity locations: - preferred_term: cytosol term: id: GO:0005829 label: cytosol role_description: >- Conventional kinesin that moves GLUT4 vesicles along microtubules in response to insulin; dominant-negative kinesin light chain blocks GLUT4 translocation. evidence: - source_id: PMID:12743033 statement: KIF5B mediates insulin-stimulated GLUT4 movements on microtubules and is required for GLUT4 translocation. supporting_text: This insulin signaling pathway regulating KIF5B function appears to be required for GLUT4 translocation to the plasma membrane. - id: myo5a_motor label: MYO5A actin motor activity participant: selector_type: GENE_PRODUCT gene_product: preferred_term: MYO5A term: id: UniProtKB:Q9Y4I1 label: Unconventional myosin-Va function: preferred_term: microfilament motor activity term: id: GO:0000146 label: microfilament motor activity locations: - preferred_term: cytosol term: id: GO:0005829 label: cytosol role_description: >- Actin-based motor that is phosphorylated by AKT2 on Ser1650; phosphorylation enhances its binding to actin and facilitates anterograde movement of GLUT4 vesicles to the surface. evidence: - source_id: PMID:17515613 statement: MYO5A is an AKT2 substrate; phosphorylated MYO5A facilitates anterograde movement of GLUT4 vesicles along actin. supporting_text: phosphorylated myosin 5a facilitates anterograde movement of GLUT4 vesicles along actin to the cell surface - id: myo1c_motor label: MYO1C actin motor activity participant: selector_type: GENE_PRODUCT gene_product: preferred_term: MYO1C term: id: UniProtKB:O00159 label: Unconventional myosin-Ic function: preferred_term: microfilament motor activity term: id: GO:0000146 label: microfilament motor activity locations: - preferred_term: cell periphery term: id: GO:0071944 label: cell periphery role_description: >- Myosin present on GLUT4 vesicles that functions in a PI3K-independent pathway moving GLUT4 vesicles to the plasma membrane; dominant-negative cargo domain blocks translocation. evidence: - source_id: PMID:12490950 statement: Myo1c functions in a PI3K-independent insulin pathway controlling movement of GLUT4 vesicles to the plasma membrane. supporting_text: myosin Myo1c functions in a PI(3)K-independent insulin signalling pathway that controls the movement of intracellular GLUT4-containing vesicles to the plasma membrane - order: 4 optional: true role: Muscle cortical actin remodelling (RAC1, PAK1, ARP2/3) node: id: cortical_actin_remodelling label: RAC1-PAK1-ARP2/3 cortical actin remodelling module_type: REGULATORY_STEP description: >- In muscle, insulin activates RAC1, which through PAK1 and the ARP2/3 actin-branching complex remodels the cortical actin meshwork beneath the plasma membrane. A dynamic cycle of ARP2/3-driven branching and cofilin (CFL1)-mediated severing — cofilin being dephosphorylated by slingshot (SSH1) and rephosphorylated by LIMK1 — is required for GLUT4 to reach the cell surface. Optional because this cortical-actin arm is prominent in muscle and dispensable for the core RabGAP-Rab-SNARE axis in adipocytes. annotons: - id: rac1_gtpase label: RAC1 GTPase activity participant: selector_type: GENE_PRODUCT gene_product: preferred_term: RAC1 term: id: UniProtKB:P63000 label: Ras-related C3 botulinum toxin substrate 1 function: preferred_term: GTPase activity term: id: GO:0003924 label: GTPase activity locations: - preferred_term: cell periphery term: id: GO:0071944 label: cell periphery role_description: >- Insulin-activated Rho GTPase required for insulin-stimulated glucose uptake in skeletal muscle; dysregulated in insulin-resistant muscle. evidence: - source_id: PMID:23423567 statement: Rac1 is required for insulin-stimulated glucose uptake in mouse and human skeletal muscle and is dysregulated in insulin resistance. supporting_text: Rac1 is a regulator of insulin-stimulated glucose uptake and a novel candidate involved in skeletal muscle insulin resistance gocam_associations: - model: gomodel:63d320cd00001536 activity: gomodel:63d320cd00001536/63d320cd00001556 title: RAC1 GTPase activity (GO:0003924); model is RAC1 degradation in cell migration, not glucose uptake - id: pak1_kinase label: PAK1 protein serine/threonine kinase activity participant: selector_type: GENE_PRODUCT gene_product: preferred_term: PAK1 term: id: UniProtKB:Q13153 label: Serine/threonine-protein kinase PAK 1 function: preferred_term: protein serine/threonine kinase activity term: id: GO:0004674 label: protein serine/threonine kinase activity locations: - preferred_term: cell periphery term: id: GO:0071944 label: cell periphery role_description: >- RAC1 effector kinase; insulin-stimulated PAK1 (Thr423) phosphorylation is reduced in insulin-resistant muscle, linking RAC1 to cortical actin remodelling. evidence: - source_id: PMID:23423567 statement: PAK is a downstream target of Rac1 whose insulin-stimulated activation is reduced in insulin-resistant muscle. supporting_text: insulin-stimulated PAK activation was decreased in both acute insulin-resistant (intralipid infusion) and chronic insulin-resistant states (obesity and diabetes) - id: arp23_nucleator label: ARP2/3 complex actin nucleation participant: selector_type: FAMILY family: preferred_term: ARP2/3 actin-nucleating complex (seven subunits) representative_members: - preferred_term: ACTR2 (Arp2) term: id: UniProtKB:P61160 label: Actin-related protein 2 - preferred_term: ACTR3 (Arp3) term: id: UniProtKB:P61158 label: Actin-related protein 3 - preferred_term: ARPC2 (p34-ARC) term: id: UniProtKB:O15144 label: Actin-related protein 2/3 complex subunit 2 function: preferred_term: structural constituent of cytoskeleton term: id: GO:0005200 label: structural constituent of cytoskeleton locations: - preferred_term: cell periphery term: id: GO:0071944 label: cell periphery role_description: >- The actin-branching nucleator downstream of Rac1; silencing Arp3 or the p34 subunit abrogates insulin-induced cortical actin remodelling and impairs GLUT4 translocation. evidence: - source_id: PMID:20739464 statement: Arp2/3, downstream of Rac, drives cortical actin polymerization required for GLUT4 translocation to the muscle cell surface. supporting_text: Arp2/3, acting downstream of Rac GTPase, is responsible for the cortical actin polymerization evoked by insulin. siRNA-mediated silencing of either Arp3 or p34 subunits of the Arp2/3 complex abrogated actin remodeling and impaired GLUT4 translocation. - order: 5 role: GLUT4 storage-vesicle docking and fusion at the plasma membrane node: id: snare_fusion label: STX4-SNAP23-VAMP2 SNARE fusion with STXBP3/STXBP4 regulation module_type: REGULATORY_STEP description: >- GSVs fuse with the plasma membrane through a SNARE complex of the vesicle SNARE VAMP2 with the plasma membrane t-SNAREs syntaxin-4 (STX4) and SNAP23. Two syntaxin-4-binding Sec1/Munc18 and tomosyn-family proteins regulate the step: Munc18c (STXBP3) and Synip (STXBP4). In the basal state Synip binds syntaxin-4 and restrains fusion; AKT2 phosphorylation of Synip on Ser99 releases it, permitting SNARE assembly. annotons: - id: stx4_tsnare label: STX4 SNAP receptor activity participant: selector_type: GENE_PRODUCT gene_product: preferred_term: STX4 term: id: UniProtKB:Q12846 label: Syntaxin-4 function: preferred_term: SNAP receptor activity term: id: GO:0005484 label: SNAP receptor activity locations: - preferred_term: plasma membrane term: id: GO:0005886 label: plasma membrane role_description: >- Plasma membrane t-SNARE for GLUT4 vesicle fusion; syntaxin-4 heterozygous mice have reduced muscle insulin-stimulated glucose uptake and GLUT4 translocation. evidence: - source_id: PMID:11375421 statement: Syntaxin 4 is required for insulin-stimulated GLUT4 translocation and glucose uptake in skeletal muscle. supporting_text: syntaxin 4 plays a critical physiological role in insulin-stimulated glucose uptake in skeletal muscle - id: snap23_tsnare label: SNAP23 SNAP receptor activity participant: selector_type: GENE_PRODUCT gene_product: preferred_term: SNAP23 term: id: UniProtKB:O00161 label: Synaptosomal-associated protein 23 function: preferred_term: SNAP receptor activity term: id: GO:0005484 label: SNAP receptor activity locations: - preferred_term: plasma membrane term: id: GO:0005886 label: plasma membrane role_description: The plasma membrane SNAP-25-family t-SNARE of the GLUT4 fusion complex. evidence: - source_id: PMID:15690082 statement: VAMP2, SNAP23 and syntaxin-4 form the SNARE complex that fuses GLUT4 vesicles with the plasma membrane. supporting_text: a soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) complex consisting of vesicle-associated membrane protein 2 (VAMP2), 23-kDa synaptosomal-associated protein (SNAP23), and syntaxin4 - id: vamp2_vsnare label: VAMP2 SNAP receptor activity participant: selector_type: GENE_PRODUCT gene_product: preferred_term: VAMP2 term: id: UniProtKB:P63027 label: Vesicle-associated membrane protein 2 function: preferred_term: SNAP receptor activity term: id: GO:0005484 label: SNAP receptor activity locations: - preferred_term: insulin-responsive compartment (GLUT4 storage vesicle) term: id: GO:0032593 label: insulin-responsive compartment role_description: >- The GSV vesicle SNARE (v-SNARE) that pairs with syntaxin-4 and SNAP23 to drive fusion; insulin promotes VAMP2 insertion into plasma membrane lipid rafts. evidence: - source_id: PMID:15690082 statement: VAMP2 is the vesicle SNARE of the GLUT4 fusion complex. supporting_text: vesicle-associated membrane protein 2 (VAMP2), 23-kDa synaptosomal-associated protein (SNAP23), and syntaxin4 - id: stxbp3_munc18c label: STXBP3 (Munc18c) syntaxin binding participant: selector_type: GENE_PRODUCT gene_product: preferred_term: STXBP3 term: id: UniProtKB:O00186 label: Syntaxin-binding protein 3 function: preferred_term: syntaxin binding term: id: GO:0019905 label: syntaxin binding locations: - preferred_term: plasma membrane term: id: GO:0005886 label: plasma membrane role_description: >- Sec1/Munc18 protein that binds syntaxin-4 and gates GLUT4 vesicle fusion; Munc18c heterozygous mice have reduced muscle GLUT4 translocation and insulin sensitivity. evidence: - source_id: PMID:15734838 statement: Munc18c is required for normal insulin-stimulated GLUT4 translocation in skeletal muscle. supporting_text: Munc18c(-/+) mice displayed significantly decreased insulin sensitivity in an insulin tolerance test and a >50% reduction in skeletal muscle insulin-stimulated GLUT4 translocation when compared with wild-type (WT) mice - id: stxbp4_synip label: STXBP4 (Synip) syntaxin binding participant: selector_type: GENE_PRODUCT gene_product: preferred_term: STXBP4 term: id: UniProtKB:Q6ZWJ1 label: Syntaxin-binding protein 4 function: preferred_term: syntaxin binding term: id: GO:0019905 label: syntaxin binding locations: - preferred_term: plasma membrane term: id: GO:0005886 label: plasma membrane role_description: >- Syntaxin-4-binding protein (Synip) that restrains fusion in the basal state; AKT2 phosphorylation on Ser99 triggers its dissociation from syntaxin-4 to permit GLUT4 translocation. evidence: - source_id: PMID:17336927 statement: Synip Ser99 phosphorylation (an Akt2 site) is required for insulin-stimulated syntaxin-4 dissociation and GLUT4 translocation. supporting_text: Synip serine 99 phosphorylation required for insulin-stimulated Glut4 translocation - order: 6 role: GLUT4 glucose transport at the plasma membrane node: id: glucose_transport label: SLC2A4 (GLUT4) D-glucose transmembrane transport module_type: TRANSPORT_STEP description: >- GLUT4 (SLC2A4) inserted into the plasma membrane transports D-glucose down its concentration gradient into the cell, the end step that produces insulin-stimulated glucose uptake. annotons: - id: slc2a4_transporter label: SLC2A4 D-glucose transmembrane transporter activity participant: selector_type: GENE_PRODUCT gene_product: preferred_term: SLC2A4 (GLUT4) term: id: UniProtKB:P14672 label: Solute carrier family 2, facilitated glucose transporter member 4 function: preferred_term: D-glucose transmembrane transporter activity term: id: GO:0055056 label: D-glucose transmembrane transporter activity processes: - preferred_term: glucose import in response to insulin stimulus term: id: GO:0044381 label: glucose import in response to insulin stimulus locations: - preferred_term: plasma membrane term: id: GO:0005886 label: plasma membrane role_description: >- The insulin-responsive facilitative glucose transporter whose arrival at the plasma membrane raises glucose uptake. evidence: - source_id: PMID:25004245 statement: GLUT4 transports glucose; its cell-surface amount sets the rate of glucose uptake in human adipocytes. supporting_text: regulation of cellular trafficking of the glucose transporter 4 (GLUT4) gocam_associations: - model: gomodel:613aae0000000885 activity: gomodel:613aae0000000885/613aae0000000906 title: SLC2A4 D-glucose transmembrane transporter activity (GO:0055056), plasma membrane, part of D-glucose transmembrane transport connections: - source: insulin_akt2_activation target: rabgap_rab_activation connection_type: CAUSES description: Activated AKT2 phosphorylates and inactivates the TBC1D4/TBC1D1 Rab GAPs. - source: rabgap_rab_activation target: gsv_movement connection_type: POSITIVELY_REGULATES description: GTP-loaded GSV Rabs recruit the cytoskeletal motors that move GLUT4 vesicles. - source: insulin_akt2_activation target: cortical_actin_remodelling connection_type: POSITIVELY_REGULATES description: >- In muscle, insulin signalling (through RAC1, parallel to the AKT2-RabGAP axis) drives cortical actin remodelling needed for GLUT4 delivery. - source: gsv_movement target: snare_fusion connection_type: PROVIDES_INPUT_FOR description: Motors deliver GSVs to the cell periphery, where they dock and fuse. - source: cortical_actin_remodelling target: snare_fusion connection_type: POSITIVELY_REGULATES description: Remodelled cortical actin supports GSV delivery and fusion at the muscle cell surface. - source: snare_fusion target: glucose_transport connection_type: PROVIDES_INPUT_FOR description: SNARE fusion inserts GLUT4 into the plasma membrane, enabling glucose transport. knowledge_gaps: - gap_statement: >- Whether the PI3K-independent CAP(SORBS1)-CBL-CRK-RAPGEF1(C3G)-RHOQ(TC10) arm is a genuine requirement for insulin-stimulated GLUT4 translocation is unresolved: it was reported as essential in 3T3-L1 adipocytes (Chiang et al. 2001), but a later RNAi study found depletion of CAP, CrkII and Cbl did not reduce insulin signalling to GLUT4 (Zhou et al. 2004). Whether the discrepancy reflects cell-line, redundancy or off-target effects, and whether TC10 acts in primary adipocytes and muscle in vivo, needs resolution by loss-of-function in physiological systems. gap_kind: - BIOLOGY