Unconventional myosin Myo1c promotes membrane fusion in a regulated exocytic pathway

Mol Cell Biol. 2004 Jun;24(12):5447-58. doi: 10.1128/MCB.24.12.5447-5458.2004.


Glucose homeostasis is controlled in part by regulation of glucose uptake into muscle and adipose tissue. Intracellular membrane vesicles containing the GLUT4 glucose transporter move towards the cell cortex in response to insulin and then fuse with the plasma membrane. Here we show that the fusion step is retarded by the inhibition of phosphatidylinositol (PI) 3-kinase. Treatment of insulin-stimulated 3T3-L1 adipocytes with the PI 3-kinase inhibitor LY294002 causes the accumulation of GLUT4-containing vesicles just beneath the cell surface. This accumulation of GLUT4-containing vesicles near the plasma membrane prior to fusion requires an intact cytoskeletal network and the unconventional myosin motor Myo1c. Remarkably, enhanced Myo1c expression under these conditions causes extensive membrane ruffling and overrides the block in membrane fusion caused by LY294002, restoring the display of GLUT4 on the cell exterior. Ultrafast microscopic analysis revealed that insulin treatment leads to the mobilization of GLUT4-containing vesicles to these regions of Myo1c-induced membrane ruffles. Thus, localized membrane remodeling driven by the Myo1c motor appears to facilitate the fusion of exocytic GLUT4-containing vesicles with the adipocyte plasma membrane.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • 3T3-L1 Cells
  • Adipocytes / drug effects
  • Adipocytes / metabolism
  • Animals
  • Chromones / pharmacology
  • Enzyme Inhibitors / pharmacology
  • Exocytosis
  • Glucose Transporter Type 4
  • Insulin / pharmacology
  • Membrane Fusion / physiology*
  • Mice
  • Molecular Motor Proteins / genetics
  • Molecular Motor Proteins / physiology
  • Monosaccharide Transport Proteins / genetics
  • Monosaccharide Transport Proteins / metabolism
  • Morpholines / pharmacology
  • Muscle Proteins*
  • Myosin Type I
  • Myosins / genetics
  • Myosins / physiology*
  • Phosphatidylinositol 3-Kinases / physiology
  • Phosphoinositide-3 Kinase Inhibitors
  • Recombinant Fusion Proteins / genetics
  • Recombinant Fusion Proteins / metabolism


  • Chromones
  • Enzyme Inhibitors
  • Glucose Transporter Type 4
  • Insulin
  • Molecular Motor Proteins
  • Monosaccharide Transport Proteins
  • Morpholines
  • Muscle Proteins
  • Myo1c protein, mouse
  • Phosphoinositide-3 Kinase Inhibitors
  • Recombinant Fusion Proteins
  • Slc2a4 protein, mouse
  • 2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one
  • Myosin Type I
  • Myosins