INSULIN REGULATION AND SELECTIVE SEGREGATION WITH GLUCOSE TRANSPORTER-4 OF THE MEMBRANE AMINOPEPTIDASE VP165 IN RAT SKELETAL-MUSCLE CELLS

vp165, a recently described member of the family of zinc-dependent mem brane aminopeptidases, is a major constituent of glucose transporter-4 (GLUT4)-containing vesicles in adipocytes and skeletal muscle. Here w e show that vp165 is expressed in L6 myoblasts and increases by 4.3-fo ld during differentiation into myotubes. The localization of vp165 in L6 myotubes was assessed by immunoblotting subcellular fractions from basal and insulin-stimulated cells and was compared to the distributio n of GLUT4. vp165 and GLUT4 were mainly concentrated in the low densit y microsomal membranes under basal conditions. Upon stimulation with i nsulin, vp165 and GLUT4 were redistributed from the low density micros omes to the plasma membrane. The majority of vp165 was found in immuno isolated GLUT4-containing vesicles, and vice versa, the majority of GL UT4 was detected in immunoisolated vp165-containing vesicles. In contr ast, the two other glucose transporter isoforms expressed in L6, GLUT1 and GLUT3, were excluded from GLUT4- and vp165-containing vesicles. T hese results suggest that in rat skeletal muscle cells, vp165 and GLUT 4 cosegregate to the same intracellular compartment and that this is d istinct from the compartment containing GLUT1 and GLUT3.