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J. Cell Biol.,
Volume 145, Number 1, April 5, 1999 141-151


* Centro de Biología Molecular "Severo Ochoa," Universidad Autónoma de Madrid and Consejo Superior de Investigaciones
Científicas, and The MAL (MAL/VIP17) proteolipid is a
nonglycosylated integral membrane protein expressed
in a restricted pattern of cell types, including T lymphocytes, myelin-forming cells, and polarized epithelial cells. Transport of the influenza virus hemagglutinin
(HA) to the apical surface of epithelial Madin-Darby
canine kidney (MDCK) cells appears to be mediated
by a pathway involving glycolipid- and cholesterol-
enriched membranes (GEMs). In MDCK cells, MAL has been proposed previously as being an element of
the protein machinery for the GEM-dependent apical
transport pathway. Using an antisense oligonucleotide-based strategy and a newly generated monoclonal antibody to canine MAL, herein we have approached the effect of MAL depletion on HA transport in MDCK
cells. We have found that MAL depletion diminishes
the presence of HA in GEMs, reduces the rate of HA
transport to the cell surface, inhibits the delivery of HA
to the apical surface, and produces partial missorting of
HA to the basolateral membrane. These effects were corrected by ectopic expression of MAL in MDCK
cells whose endogenous MAL protein was depleted.
Our results indicate that MAL is necessary for both
normal apical transport and accurate sorting of HA.
Department of Immunology and Oncology, Centro Nacional de Biotecnología, Consejo Superior de
Investigaciones Científicas, Cantoblanco, 28049-Madrid, Spain
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