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J. Biol. Chem., Vol. 276, Issue 38, 35990-35994, September 21, 2001
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From the Adipose cells produce and secrete several
physiologically important proteins, such as lipoprotein lipase
(LPL), leptin, adipsin, Acrp30, etc. However, secretory pathways in
adipocytes have not been characterized, and vesicular carriers
responsible for the accumulation and transport of secreted proteins
have not been identified. We have compared the intracellular
localization of two proteins secreted from adipose cells: leptin and
LPL. Adipocytes accumulate large amounts of both proteins, suggesting
that neither of them is targeted to the constitutive secretory pathway.
By means of velocity centrifugation in sucrose gradients, equilibrium density centrifugation in iodixanol gradients, and immunofluorescence confocal microscopy, we determined that LPL and leptin were
localized in different membrane structures. LPL was found mainly in the endoplasmic reticulum with a small pool being present in low density membrane vesicles that may represent a secretory compartment in adipose cells. Virtually all intracellular leptin was localized in
these low density secretory vesicles. Insulin-sensitive Glut4 vesicles
did not contain either LPL or leptin. Thus, secretion from adipose
cells is controlled both at the exit from the endoplasmic reticulum as well as at the level of "downstream" secretory vesicles.
Lipoprotein Lipase and Leptin Are Accumulated in Different
Secretory Compartments in Rat Adipocytes*
,
Boston University School of Medicine,
Boston, Massachusetts 02118, § University of Lausanne,
Lausanne, Switzerland, CH 1005, and ¶ Rutgers University, New
Brunswick, New Jersey 08901
*
This work was supported by Research Grants DK52057 and
DK56736 from the National Institutes of Health and by a research grant from the American Diabetes Association (to K. V. K.).The costs of publication of this
article were defrayed in part by the
payment of page charges. The article
must therefore be hereby marked
"advertisement" in
accordance with 18 U.S.C. Section
1734 solely to indicate this fact.
To whom correspondence should be sent: Boston University
School of Medicine, Dept. of Biochemistry, K121, 715 Albany St., Boston, MA 02118. Tel.: 617-638-5049; Fax: 617-638-5339; E-mail: kandror@biochem.bumc.bu.edu.
Copyright © 2001 by The American Society for Biochemistry and Molecular Biology, Inc.
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