GLUT4 vesicle recruitment and fusion are differentially regulated by Rac, AS160, and Rab8A in muscle cells.
Insulin increases glucose uptake into muscle by enhancing the surface recycling of GLUT4 transporters. In myoblasts, insulin signals bifurcate downstream of phosphatidylinositol 3-kinase into separate Akt and Rac/actin arms. Akt-mediated Rab-GAP AS160 phosphorylation and Rac/actin are required for net insulin gain of GLUT4, but the specific steps (vesicle recruitment, docking or fusion) regulated by Rac, actin dynamics, and AS160 target Rab8A are unknown. In L6 myoblasts expressing GLUT4myc, blocking vesicle fusion by tetanus toxin cleavage of VAMP2 impeded GLUT4myc membrane insertion without diminishing its build-up at the cell periphery. Conversely, actin disruption by dominant negative Rac or Latrunculin B abolished insulin-induced surface and submembrane GLUT4myc accumulation. Expression of non-phosphorylatable AS160 (AS160-4P) abrogated membrane insertion of GLUT4myc and partially reduced its cortical build-up, an effect magnified by selective Rab8A knockdown. We propose that insulin-induced actin dynamics participates in GLUT4myc vesicle retention beneath the membrane, whereas AS160 phosphorylation is essential for GLUT4myc vesicle-membrane docking/fusion and also contributes to GLUT4myc cortical availability through Rab8A.
Randhawa
Varinder K
VK
Program in Cell Biology, Hospital for Sick Children, Toronto, Ontario M5G 1X8, Canada.
Ishikura
Shuhei
S
Talior-Volodarsky
Ilana
I
Cheng
Alex W P
AW
Patel
Nish
N
Hartwig
John H
JH
Klip
Amira
A
D000199:Actins / Q000235:genetics / Q000378:metabolism; D000818:Animals; D019086:Bridged Bicyclo Compounds, Heterocyclic / Q000494:pharmacology; D020690:GTPase-Activating Proteins / Q000235:genetics / Q000378:metabolism*; D015870:Gene Expression; D051275:Glucose Transporter Type 4 / Q000235:genetics / Q000378:metabolism*; D008561:Membrane Fusion / Q000187:drug effects / Q000502:physiology*; D051379:Mice; D032446:Myoblasts / Q000166:cytology / Q000378:metabolism*; D022142:Secretory Vesicles / Q000235:genetics / Q000378:metabolism*; D053778:Thiazolidines / Q000494:pharmacology; D050988:Vesicle-Associated Membrane Protein 2 / Q000235:genetics / Q000378:metabolism; D020691:rab GTP-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D020744:rac GTP-Binding Proteins / Q000235:genetics / Q000378:metabolism*
D000199:Actins; D019086:Bridged Bicyclo Compounds, Heterocyclic; D020690:GTPase-Activating Proteins; D051275:Glucose Transporter Type 4; C521976:Rab8 protein, mouse; C495693:Slc2a4 protein, mouse; C505647:Tbc1d4 protein, mouse; D053778:Thiazolidines; D050988:Vesicle-Associated Membrane Protein 2; C494808:vesicle-associated membrane protein 2, mouse; D020691:rab GTP-Binding Proteins; D020744:rac GTP-Binding Proteins; C037068:latrunculin B