Glucose Transporter 4 (GLUT4)

GLUT4 is the insulin-regulated glucose transporter found in adipose tissues and striated muscle (skeletal and cardiac) that is responsible for insulin-regulated glucose disposal.In the absence of insulin, GLUT4 is sequestered in the interior of muscle and fat cells within lipid bilayers of vesicles. Insulin induces the translocation of GLUT4 from intracellular storage sites to the plasma membrane. Insulin binds to the insulin receptor in its dimeric form.

The receptor phosphorylates and subsequently activates IRS-1, which converts PIP2 to PIP3. PIP3 is bound to PKB (protein kinase B), signaling for PDK1 to phosphorylate PKB. Once phosphorylated, PKB is in its active form and phosphorylates other targets that stimulate GLUT4 to be expressed on the plasma membrane.