Gabathuler R, Alimonti J, Zhang Q J, Kolaitis G, Reid G, Jefferies W A
Biotechnology Laboratory, University of British Columbia, Vancouver, British Columbia, Canada V6T1Z3.
J Cell Biol. 1998 Jan 12;140(1):17-27. doi: 10.1083/jcb.140.1.17.
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 degrees 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.
MHC I类蛋白在内质网中与肽段组装。这些肽段主要源自细胞质蛋白，可能是通过蛋白酶体（一种多催化蛋白酶复合体）的作用产生的。肽段通过与抗原加工相关的转运体（TAP）转运至内质网，并在转运至细胞表面之前与MHC I类分子结合。在此，我们使用一种新的功能测定方法来证明源自水疱性口炎病毒核蛋白（VSV-N）抗原的肽段会从细胞中主动分泌。这种分泌途径依赖于TAP转运体的表达，但不依赖于供体细胞的MHC基因型。此外，MHC I类分子的表达和转运并非必需。这条新途径对蛋白质分泌抑制剂布雷菲德菌素A（BFA）以及21摄氏度的温度阻断敏感，并且也会被代谢毒物叠氮化物和蛋白质合成抑制剂依米丁抑制。这些数据支持存在一种利用TAP转运体而非内质网转运体进入分泌途径的新型肽段分泌形式。最后，我们认为在未感染细胞附近这种肽段的释放，我们称之为替代抗原加工，可能有助于各种免疫和分泌现象。
