VIP17/MAL, a lipid raft-associated protein, is involved in apical transport in MDCK cells

^*European Molecular Biology Laboratory, Cell Biology and Biophysics Programme, D69012 Heidelberg and Max Planck Institute for Molecular Cell Biology and Genetics, Dresden, Germany; and ^‡Department of Pathology, Massachusetts General Hospital, Boston, MA 02114

Contributed by Kai Simons

Abstract

Apical proteins are sorted and delivered from the trans-Golgi network to the plasma membrane by a mechanism involving sphingolipid–cholesterol rafts. In this paper, we report the effects of changing the levels of VIP17/MAL, a tetraspan membrane protein localized to post-Golgi transport containers and the apical cell surface in MDCK cells. Overexpression of VIP17/MAL disturbed the morphology of the MDCK cell layers by increasing apical delivery and seemingly expanding the apical cell surface domains. On the other hand, expression of antisense RNA directed against VIP17/MAL caused accumulation in the Golgi and/or impaired apical transport of different apical protein markers, i.e., influenza virus hemagglutinin, the secretory protein clusterin (gp80), the transmembrane protein gp114, and a glycosylphosphatidylinositol-anchored protein. However, antisense RNA expression did not affect the distribution of E-cadherin to the basolateral surface. Because VIP17/MAL associates with sphingolipid–cholesterol rafts, these data provide functional evidence that this protein is involved in apical transport and might be a component of the machinery clustering lipid rafts with apical cargo to form apical transport carriers.

Footnotes

↵ † Present address: Department of Neuroscience, DIBIT, Scientific Institute Hospital San Raffaele, 20132 Milan, Italy.
↵ § To whom reprint requests should be addressed. e-mail: Simons{at}embl-heidelberg.de.
This contribution is part of the special series of Inaugural Articles by members of the National Academy of Sciences elected on April 29, 1998.
ABBREVIATIONS:

HA,

hemagglutinin;

CHAPS,

3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonate;

DIG,

detergent-insoluble glycosphingolipid complex;

IPTG,

isopropylthio-β-d-galactoside;

MDCK,

Madin-Darby canine kidney;

SNAP23,

synaptosomal-associated 23-kDa protein;

SNARE,

SNAP receptor;

TI-VAMP,

tetanus toxin-insensitive vesicle-associated membrane protein;

VIP,

vesicular integral protein;

TGN,

trans-Golgi network;

GFP,

green fluorescent protein;

GPI,

glycophosphatidylinositol