Compartmentalization of protein traffic in insulin-sensitive
cells.
Kandror, Konstantin V., and Paul F. Pilch.
Boston University Medical School, 80 East Concord Street, Boston,
MA 02118
APStracts 3:0054E, 1996.
Insulin-sensitive cells, adipocytes and myocytes, translocate a number
of intracellular proteins to the cell surface in response to insulin.
Among these proteins are glucose transporters 1 and 4, receptors for
IGF-II/Man-6-P and transferrin, the aminopeptidase gp160, caveolin,
and a few others. In the case of insulin-activated glucose transport,
this translocation has been proven to be the major, if not the only
regulatory mechanism of this process. It seems likely that the cell
surface recruitment of the IGF-II/Man-6-P and transferrin receptors
also serves the nutritional needs of cells, whereas the physiological
role of the aminopeptidase gp160 remains uncertain. Analysis of the
compartmentalization and trafficking pathways of translocatable
proteins in fat cells identified more than one population of
recycling vesicles, although all have identical sedimentation
coefficients and buoyant densities in vitro. GLUT4-containing
vesicles include essentially all the intracellular GLUT4, gp160, and
the acutely recycling populations of receptors for IGF-II/Man-6-P and
transferrin. Besides these proteins which can be considered as
vesicle "cargo", GLUT4-containing vesicles have other
components, like Scamps, Rab(s), and VAMP/cellubrevin which are
ubiquitous to secretory vesicles and granules from different tissues.
GLUT1 and caveolin are excluded from GLUT4-containing vesicles and
form different vesicular populations of unknown polypeptide
composition. In skeletal muscle, two independent populations of
GLUT4-containing vesicles are found: insulin-sensitive and exercise
-sensitive which explains the additive effect of insulin and exercise
on glucose uptake. Both vesicular populations are similar to each
other and to analogous vesicles in fat cells.
Received 11 December 1995; accepted in final form 22 February
1996.
APS Manuscript Number E578-5.
Article publication pending Am. J. Physiol. (Endocrinol. Metab.).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 20 March 96