Unique Expression of Major Histocompatibility Complex Class I Proteins in the Absence of Glucose Trimming and Calnexin Association

doi:10.1074/jbc.270.48.29025

Unique Expression of Major Histocompatibility Complex Class I Proteins in the Absence of Glucose Trimming and Calnexin Association *

From the Experimental Immunology Branch, NCI, National Institutes of Health, Bethesda, Maryland 20892-1260

^§ To whom correspondence should be addressed. Tel.: 301-496-5857; Fax: 301-496-0887.

Abstract

Recent evidence indicates that efficient expression of major histocompatibility complex (MHC) complexes requires their interaction with the resident endoplasmic reticulum (ER) chaperone calnexin, which for certain proteins functions as a lectin specific for monoglucosylated glycans. In the current report, we studied the expression of MHC class I proteins in BW wild type thymoma cells (BW WT) and glucosidase II-deficient BW PHAR2.7 cells. Consistent with a requirement for glucose (Glc) trimming for interaction of class I proteins with calnexin, we found that nascent H-2K proteins associated with calnexin in untreated BW WT cells, but not in BW WT cells treated with the glucosidase inhibitor castanospermine (cas), or in untreated glucosidase II-deficient BW PHAR2.7 cells. Suprisingly, we found that H-2K expression occurred with similar efficiency in BW PHAR2.7 cells as in BW WT cells and that formation of nascent H-2K complexes was perturbed by cas treatment in BW WT cells but not in BW PHAR2.7 cells. Finally, it was noted that expression of the molecular chaperone Bip was markedly increased in BW PHAR2.7 cells relative to BW WT cells, which is suggested to play a role in regulating the expression of H-2K complexes in BW PHAR2.7 cells. The current study demonstrates that Glc trimming is required for efficient interaction of nascent H-2K proteins with calnexin; that expression of MHC class I proteins can, under certain conditions, proceed effectively in the absence of Glc trimming and calnexin association; and that Bip expression is markedly increased under conditions where diglucosylated glycans persist on nascent glycoproteins within the ER. These data are consistent with the hypothesis that alternative oligomerization pathways exist for class I proteins within the quality control system of the ER that have differential requirements for removal of Glc residues from nascent glycan chains.

Footnotes

↵* The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore by hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
↵¹ The abbreviations used are:

MHC

major histocompatibility complex

Bip

binding protein

Endo H

endoglycosidase H

cas

castanospermine

ER

endoplasmic reticulum

Glc

glucose

GlcNAc

N-acetylglucosamine

HC

heavy chain

Man

mannose

mAb

monoclonal antibody

NEPHGE

nonequilibrium pH gradient gel electrophoresis

PAGE

polyacrylamide gel electrophoresis.
↵²J. P. Balow and K. P. Kearse, unpublished observations.
↵³J. Weissman and K. P. Kearse, unpublished observations.
- Received August 1, 1995.
- Revision received September 27, 1995.