Involvement of annexin ii in exocytosis of lamellar bodies from
alveolar epithelial type ii cells.
Liu, Lin, Mengshu Wang, Aron B. Fisher, and Un-Jin P. Zimmerman.
Institute for Environmental Medicine, University of Pennsylvania,
Medical Center, Philadelphia, PA 19104
APStracts 2:0211L, 1995.
Annexins are a family of Ca2+- and phospholipid-binding proteins that
have been implicated in exocytosis. In the present study, we
investigated the participation of selected annexins in exocytosis of
lamellar bodies by examining their liposome aggregation property and
ability to reconstitute surfactant secretion from permeabilized rat
lung alveolar type II cells. Annexins I, II, III and VI were
demonstrated in type II cells by immunoblot analysis, but, annexin IV
and V were not found. Annexins I-IV mediated liposome aggregation in
the presence of 1 mM Ca2+. However, only annexin II tetramer had
aggregation activity at 10 [mu]M Ca2+. Annexins V and VI had
negligible aggregation activity at any Ca2+ concentrations (up to 1
mM Ca2+). To study reconstitution of secretion by annexins, isolated
type II cells were permeabilized with 40 [mu]M [beta]-escin. Under
these conditions, the permeabilized cells released about 30-40%
lactic acid dehydrogenase into the medium. An undetermined fraction
of cellular annexin content was lost during permeabilization.
However, lamellar bodies in the permeabilized type II cells stained
appropriately with the fluorescent dyes, nile red and quinacrine,
indicating that they were intact. These permeabilized cells were
secretion-competent, since phosphatidylcholine (PC) secretion was
stimulated by 0.2-1.0 [mu]M Ca2+. Addition of an exogenous annexin
mixture enhanced PC secretion from the permeabilized type II cells
with maximal stimulation at 0.5 [mu]M Ca2+. Of six purified annexins
(I-VI) tested for their ability to reconstitute secretion from the
permeabilized cells, only annexin II was effective. Our results
suggest that annexin II is necessary for exocytosis of lamellar
bodies.
Received 26 June 1995; accepted in final form 6 November 1995.
APS Manuscript Number L200-5.
Article publication pending Am. J. Physiol. (Lung Cell. Mol.
Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 30 November 95