Insulin-induced translocation of CD36 to the plasma membrane is reversible and shows similarity to that of GLUT4

Abstract

In cardiac and skeletal muscles, insulin regulates the uptake of long-chain fatty acid (LCFA) via the putative LCFA transporter CD36. Biochemical studies propose an insulin-induced translocation of CD36 from intracellular pools to the plasma membrane (PM), similar to glucose transporter 4 (GLUT4) translocation. To characterize insulin-induced CD36 translocation in intact cells, Chinese hamster ovary (CHO) cells stably expressing CD36 or myc-tagged GLUT4 (GLUT4myc) were created. Immuno-fluorescence microscopy revealed CD36 to be located both intracellularly (in--at least partially--different compartments than GLUT4myc) and at the PM. Upon stimulation with insulin, CD36 translocated to a PM localization similar to that of GLUT4myc; the increase in PM CD36 content, as quantified by surface-protein biotinylation, amounted to 1.7-fold. The insulin-induced CD36 translocation was shown to be phosphatidylinositol-3 kinase-dependent, and reversible (as evidenced by insulin wash-out) in a similar time frame as that for GLUT4. The expression of GLUT4myc in non-stimulated cells, and the insulin-induced increase in PM GLUT4myc correlated with increased deoxyglucose uptake. By contrast, CD36 expression in non-stimulated cells and the insulin-induced increase in PM CD36 were not paralleled by a rise in LCFA uptake, suggesting that in these cells, such increase requires additional proteins, or a protein activation step. Taken together, this study is the first to present morphological evidence for CD36 translocation, and shows this process to resemble GLUT4 translocation.