Js. Bogan et Hf. Lodish, Two compartments for insulin-stimulated exocytosis in 3T3-L1 adipocytes defined by endogenous ACRP30 and GLUT4, J CELL BIOL, 146(3), 1999, pp. 609-620
Insulin stimulates adipose cells both to secrete proteins and to translocat
e the GLUT4 glucose transporter from an intracellular compartment to the pl
asma membrane. We demonstrate that whereas insulin stimulation of 3T3-L1 ad
ipocytes has no effect on secretion of the alpha 3 chain of type VI collage
n, secretion of the protein hormone adipocyte complement related protein of
30 kD (ACRP30) is markedly enhanced, Like GLUT4, regulated exocytosis of A
CRP30 appears to require phosphatidylinositol-3-kinase activity, since insu
lin-stimulated ACRP30 secretion is blocked by pharmacologic inhibitors of t
his enzyme. Thus, 3T3-L1 adipocytes possess a regulated secretory compartme
nt containing ACRP30. Whether GLUT4 recycles to such a compartment has been
controversial. We present deconvolution immunofluorescence microscopy data
demonstrating that the subcellular distributions of ACRP30 and GLUT4 are d
istinct and nonoverlapping; in contrast, those of GLUT4 and the transferrin
receptor overlap. Together with supporting evidence that GLUT4 does not re
cycle to a secretory compartment via the trans-Golgi network, we conclude t
hat there are at least two compartments that undergo insulin-stimulated exo
cytosis in 3T3-L1 adipocytes: one for ACRP30 secretion and one for GLUT4 tr
anslocation.