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© The Rockefeller University Press, 0021-9525/1999//609 $5.00
The Journal of Cell Biology, Volume 146, Number 3, , 1999 609-620

Original Article

Two Compartments for Insulin-Stimulated Exocytosis in 3t3-L1 Adipocytes Defined by Endogenous Acrp30 and Glut4



Jonathan S. Bogana,b and Harvey F. Lodisha,c

a Whitehead Institute for Biomedical Research, Cambridge, Massachusetts 02142-1479
b Diabetes Unit, Department of Medicine, Massachusetts General Hospital and Harvard Medical School, Boston, Massachusetts 02114
c Department of Biology, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139
Whitehead Institute for Biomedical Research, 9 Cambridge Center, Room 567F, Cambridge, MA 02142-1479.(617) 258-6768(617) 258-5216

lodish{at}wi.mit.edu

Insulin stimulates adipose cells both to secrete proteins and to translocate the GLUT4 glucose transporter from an intracellular compartment to the plasma membrane. We demonstrate that whereas insulin stimulation of 3T3-L1 adipocytes has no effect on secretion of the {alpha}3 chain of type VI collagen, secretion of the protein hormone adipocyte complement related protein of 30 kD (ACRP30) is markedly enhanced. Like GLUT4, regulated exocytosis of ACRP30 appears to require phosphatidylinositol-3-kinase activity, since insulin-stimulated ACRP30 secretion is blocked by pharmacologic inhibitors of this enzyme. Thus, 3T3-L1 adipocytes possess a regulated secretory compartment 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 distinct and nonoverlapping; in contrast, those of GLUT4 and the transferrin receptor overlap. Together with supporting evidence that GLUT4 does not recycle to a secretory compartment via the trans-Golgi network, we conclude that there are at least two compartments that undergo insulin-stimulated exocytosis in 3T3-L1 adipocytes: one for ACRP30 secretion and one for GLUT4 translocation.

Key Words: exocytosis • monosaccharide transport proteins • insulin • adipose tissue • secretion

© 1999 The Rockefeller University Press

1.used in this paper: ACRP30, adipocyte complement related protein of 30 kD; GLUT, glucose transporter; PI-3 kinase, phosphatidylinositol-3-kinase; TfnR, transferrin receptor


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