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J Biol Chem, Vol. 275, Issue 3, 2029-2036, January 21, 2000
From the Pantophysin, a protein related to the
neuroendocrine-specific synaptophysin, recently has been identified in
non-neuronal tissues. In the present study, Northern blots showed that
pantophysin mRNA was abundant in adipose tissue and increased
during adipogenesis of 3T3-L1 cells. Immunoblot analysis of subcellular
fractions showed pantophysin present exclusively in membrane fractions
and relatively evenly distributed in the plasma membrane and internal membrane fractions. Sucrose gradient ultracentrifugation demonstrated that pantophysin and GLUT4 exhibited overlapping distribution profiles.
Furthermore, immunopurified GLUT4 vesicles contained pantophysin, and
both GLUT4 and pantophysin were depleted from this vesicle population
following treatment with insulin. Additionally, a subpopulation of
immunopurified pantophysin vesicles contained insulin-responsive GLUT4.
Consistent with the interaction of synaptophysin with
vesicle-associated membrane protein 2 in neuroendocrine tissues, pantophysin associated with vesicle-associated membrane protein 2 in
adipocytes. Furthermore, in [32P]orthophosphate-labeled
cells, pantophysin was phosphorylated in the basal state. This
phosphorylation was unchanged in response to insulin; however, insulin
stimulated the phosphorylation of a 77-kDa protein associated with
Pantophysin Is a Phosphoprotein Component of Adipocyte Transport
Vesicles and Associates with GLUT4-containing Vesicles*
,
,
,
Research Division, Joslin Diabetes Center
and Department of Medicine, Harvard Medical School,
Boston, Massachusetts 02215, the § Department of Cell
Biology, Albert Einstein College of Medicine,
New York, New York 10461, and ¶ The Whitehead Institute for
Biomedical Research, Cambridge, Massachusetts 02142
-pantophysin immunoprecipitates. Although the functional role of
pantophysin in vesicle trafficking is unclear, its presence on
GLUT4 vesicles is consistent with the emerging role of soluble
N-ethylmaleimide-sensitive protein receptor (SNARE) factor
complex and related proteins in regulated vesicle transport in
adipocytes. In addition, pantophysin may provide a marker for
the analysis of other vesicles in adipocytes.
*
This work was supported by National Institutes of Health
Grants DK51668 (to B. C.) and DK47618 (to H. F. L.) and National Research Service Award HD07938 (to C. C. B.).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 addressed: Joslin Diabetes
Cntr., One Joslin Place, Boston, MA 02215. Tel.: 617-732-2629; Fax:
617-735-1970; E-mail: Bentley.Cheatham@joslin.harvard.edu.
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