Calreticulin controls the rate of assembly of CD1d molecules in the endoplasmic reticulum.
CD1d is an MHC class I-like molecule comprised of a transmembrane glycoprotein (heavy chain) associated with β(2)-microglobulin (β(2)m) that presents lipid antigens to NKT cells. Initial folding of the heavy chain involves its glycan-dependent association with calreticulin (CRT), calnexin (CNX), and the thiol oxidoreductase ERp57, and is followed by assembly with β(2)m to form the heterodimer. Here we show that in CRT-deficient cells CD1d heavy chains convert to β(2)m-associated dimers at an accelerated rate, indicating faster folding of the heavy chain, while the rate of intracellular transport after assembly is unaffected. Unlike the situation with MHC class I molecules, antigen presentation by CD1d is not impaired in the absence of CRT. Instead, there are elevated levels of stable and functional CD1d on the surface of CRT-deficient cells. Association of the heavy chains with the ER chaperones Grp94 and Bip is observed in the absence of CRT, and these may replace CRT in mediating CD1d folding and assembly. ER retention of free CD1d heavy chains is impaired in CRT-deficient cells, allowing their escape and subsequent expression on the plasma membrane. However, these free heavy chains are rapidly internalized and degraded in lysosomes, indicating that β(2)m association is required for the exceptional resistance of CD1d to lysosomal degradation that is normally observed.
Zhu
Yajuan
Y
Department of Immunobiology, Howard Hughes Medical Institute, Yale University School of Medicine, New Haven, Connecticut 06520-8011, USA.
Zhang
Wei
W
Veerapen
Natacha
N
Besra
Gurdyal
G
Cresswell
Peter
P
D000818:Animals; D017951:Antigen Presentation / Q000502:physiology; D055610:Antigens, CD1d / Q000235:genetics / Q000276:immunology / Q000378:metabolism*; D064032:Calbindin 2; D037281:Calnexin / Q000235:genetics / Q000276:immunology / Q000378:metabolism; D002460:Cell Line; D002462:Cell Membrane / Q000235:genetics / Q000276:immunology / Q000378:metabolism; D004721:Endoplasmic Reticulum / Q000235:genetics / Q000276:immunology / Q000378:metabolism*; D000091342:Endoplasmic Reticulum Chaperone BiP; D005786:Gene Expression Regulation / Q000502:physiology; D006360:Heat-Shock Proteins / Q000235:genetics / Q000276:immunology / Q000378:metabolism; D015395:Histocompatibility Antigens Class I / Q000235:genetics / Q000276:immunology / Q000378:metabolism; D006801:Humans; D008055:Lipids / Q000235:genetics / Q000276:immunology; D008247:Lysosomes / Q000235:genetics / Q000276:immunology / Q000378:metabolism; D008562:Membrane Glycoproteins / Q000235:genetics / Q000276:immunology / Q000378:metabolism; D051379:Mice; D019704:Protein Disulfide-Isomerases / Q000235:genetics / Q000276:immunology / Q000378:metabolism; D064030:S100 Calcium Binding Protein G / Q000235:genetics / Q000276:immunology / Q000378:metabolism*; D001613:beta 2-Microglobulin / Q000235:genetics / Q000276:immunology / Q000378:metabolism*
D055610:Antigens, CD1d; C526877:CD1D protein, human; D064032:Calbindin 2; C526879:Cd1d1 protein, mouse; D000091342:Endoplasmic Reticulum Chaperone BiP; D006360:Heat-Shock Proteins; D015395:Histocompatibility Antigens Class I; D008055:Lipids; D008562:Membrane Glycoproteins; D064030:S100 Calcium Binding Protein G; D001613:beta 2-Microglobulin; C053387:endoplasmin; D037281:Calnexin; C513195:Pdia3 protein, mouse; D019704:Protein Disulfide-Isomerases; C085868:PDIA3 protein, human