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J. Cell Biol.,
Volume 140, Number 1, January 12, 1998 17-27
Biotechnology Laboratory and the Departments of Medical Genetics, Microbiology, and Zoology, University of British
Columbia, Vancouver, British Columbia, Canada V6T1Z3
MHC class I proteins assemble with peptides
in the ER. The peptides are predominantly generated
from cytoplasmic proteins, probably by the action of
the proteasome, a multicatalytic proteinase complex.
Peptides are translocated into the ER by the transporters associated with antigen processing (TAP), and bind
to the MHC class I molecules before transport to the
cell surface. Here, we use a new functional assay to
demonstrate that peptides derived from vesicular stomatitis virus nucleoprotein (VSV-N) antigen are actively secreted from cells. This secretion pathway is dependent on the expression of TAP transporters, but is
independent of the MHC genotype of the donor cells.
Furthermore, the expression and transport of MHC
class I molecules is not required. This novel pathway is
sensitive to the protein secretion inhibitors brefeldin A
(BFA) and a temperature block at 21°C, and is also inhibited by the metabolic poison, azide, and the protein
synthesis inhibitor, emetine. These data support the existence of a novel form of peptide secretion that uses
the TAP transporters, as opposed to the ER translocon,
to gain access to the secretion pathway. Finally, we suggest that this release of peptides in the vicinity of uninfected cells, which we term surrogate antigen processing, could contribute to various immune and secretory
phenomena.
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