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Calreticulin controls the rate of assembly of CD1d molecules in the endoplasmic reticulum.

ABSTRACT: CD1d is an MHC class I-like molecule comprised of a transmembrane glycoprotein (heavy chain) associated with ?(2)-microglobulin (?(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 ?(2)m to form the heterodimer. Here we show that in CRT-deficient cells CD1d heavy chains convert to ?(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 ?(2)m association is required for the exceptional resistance of CD1d to lysosomal degradation that is normally observed.

SUBMITTER: Zhu Y

PROVIDER: S-EPMC2992262 | biostudies-literature | 2010 Dec

REPOSITORIES: biostudies-literature

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Calreticulin controls the rate of assembly of CD1d molecules in the endoplasmic reticulum.

Zhu Yajuan Y Zhang Wei W Veerapen Natacha N Besra Gurdyal G Cresswell Peter P

The Journal of biological chemistry 20100922 49

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 acc ...[more]

PMID: 20861015

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Project description:BackgroundCalreticulin (CRT) is a chaperone protein, which aids correct folding of glycosylated proteins in the endoplasmic reticulum (ER). Under conditions of ER stress, CRT is upregulated and may be displayed on the surface of cells or be secreted. This 'ecto-CRT' may activate the innate immune response or it may aid clearance of apoptotic cells. Our and other studies have demonstrated upregulation of ER stress markers CHOP, BiP, ATF4, XBP1 and phosphorylated e-IF2 alpha (p-eIF2 alpha) in biopsy and post-mortem human multiple sclerosis (MS) samples. We extend this work by analysing changes in expression of CRT, BiP, CHOP, XBP1 and p-eIF2 alpha in a rat model of inflammatory demyelination. Demyelination was induced in the spinal cord by intradermal injection of recombinant mouse MOG mixed with incomplete Freund's adjuvant (IFA) at the base of the tail. Tissue samples were analysed by semi-quantitative scoring of immunohistochemically stained frozen tissue sections. Data generated following sampling of tissue from animals with spinal cord lesions, was compared to that obtained using tissue derived from IFA- or saline-injected controls. CRT present in rat serum and in a cohort of human serum derived from 14 multiple sclerosis patients and 11 healthy controls was measured by ELISA.ResultsStained tissue scores revealed significantly (p<0.05) increased amounts of CRT, CHOP and p-eIF2 alpha in the lesion, lesion edge and normal-appearing white matter when compared to controls. CHOP and p-eIF2 alpha were also significantly raised in regions of grey matter and the central canal (p<0.05). Immunofluorescent dual-label staining confirmed expression of these markers in astrocytes, microglia or neurons. Dual staining of rat and human spinal cord lesions with Oil Red O and CRT antibody showed co-localisation of CRT with the rim of myelin fragments. ELISA testing of sera from control and EAE rats demonstrated significant down-regulation (p<0.05) of CRT in the serum of EAE animals, compared to saline and IFA controls. This contrasted with significantly increased amounts of CRT detected in the sera of MS patients (p<0.05), compared to controls.ConclusionThis data highlights the potential importance of CRT and other ER stress proteins in inflammatory demyelination.

Dataset Information

Calreticulin controls the rate of assembly of CD1d molecules in the endoplasmic reticulum.

Publications

Calreticulin controls the rate of assembly of CD1d molecules in the endoplasmic reticulum.

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