Beyond lectins: the calnexin/calreticulin chaperone system of the endoplasmic reticulum

Williams, David B.

doi:10.1242/jcs.02856

Cited by 424 publications

(376 citation statements)

References 102 publications

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“…These N-glycans are recognized by ER lectin-like chaperones calnexin (CNX) and/ or calreticulin (CRT), which promote proper folding by preventing aggregation and premature export from the ER (Fig. 1C) (Williams 2006;. Trimming of the innermost glucose residue by glucosidase II releases those polypeptides from CNX/CRT.…”

Section: Protein Folding and Posttranslational Modification Glycosylamentioning

confidence: 99%

Protein Folding and Quality Control in the ER

Araki

Nagata

2011

Cold Spring Harbor Perspectives in Biology

317

285

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The endoplasmic reticulum (ER) uses an elaborate surveillance system called the ER quality control (ERQC) system. The ERQC facilitates folding and modification of secretory and membrane proteins and eliminates terminally misfolded polypeptides through ER-associated degradation (ERAD) or autophagic degradation. This mechanism of ER protein surveillance is closely linked to redox and calcium homeostasis in the ER, whose balance is presumed to be regulated by a specific cellular compartment. The potential to modulate proteostasis and metabolism with chemical compounds or targeted siRNAs may offer an ideal option for the treatment of disease.

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Section: Protein Folding and Posttranslational Modification Glycosylamentioning

confidence: 99%

Protein Folding and Quality Control in the ER

Araki

Nagata

2011

Cold Spring Harbor Perspectives in Biology

317

285

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“…We also observed aberrant intracellular localization of the expressed hGGT2 proteins. These data indicate that the glycosylated hGGT2 propeptides likely fail to fold properly and arrest in the ER where they are shepherded by resident chaperones for targeted degradation (31,54). The only evidence that hGGT2 transcripts are actively translated in vivo is a report in which a single tryptic peptide unique to the amino-acid sequence of hGGT2 was identified during a high-throughput mass spectrometric characterization of human liver glycopeptides (7).…”

Section: Discussionmentioning

confidence: 99%

Human GGT2 Does Not Autocleave into a Functional Enzyme: A Cautionary Tale for Interpretation of Microarray Data on Redox Signaling

West

Wickham

Parks

et al. 2013

Antioxidants & Redox Signaling

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Aims: Human c-glutamyltranspeptidase 1 (hGGT1) is a cell-surface enzyme that is a regulator of redox adaptation and drug resistance due to its glutathionase activity. The human GGT2 gene encodes a protein that is 94% identical to the amino-acid sequence of hGGT1. Transcriptional profiling analyses in a series of recent publications have implicated the hGGT2 enzyme as a modulator of disease processes. However, hGGT2 has never been shown to encode a protein with enzymatic activity. The aim of this study was to express the protein encoded by hGGT2 and each of its known variants and to assess their stability, cellular localization, and enzymatic activity. Results: We discovered that the proteins encoded by hGGT2 and its variants are inactive propeptides. We show that hGGT2 cDNAs are transcribed with a similar efficiency to hGGT1, and the expressed propeptides are N-glycosylated. However, they do not autocleave into heterodimers, fail to localize to the plasma membrane, and do not metabolize c-glutamyl substrates. Substituting the coding sequence of hGGT1 to conform to alterations in a CX 3 C motif encoded by hGGT2 mRNAs disrupted autocleavage of the hGGT1 propeptide into a heterodimer, resulting in loss of plasma membrane localization and catalytic activity. Innovation and Conclusions: This is the first study to evaluate hGGT2 protein. The data show that hGGT2 does not encode a functional enzyme. Microarray data which have reported induction of hGGT2 mRNA should not be interpreted as induction of a protein that has a role in the metabolism of extracellular glutathione and in maintaining the redox status of the cell.

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“…28 The aequorin-based measurement, applied in our study, is based on a protocol which includes (i) pre-incubation of cells with the aequorin cofactor coelenterazine n, following complete Ca 2 þ depletion of the ER in Ca 2 þ -free medium; (ii) refilling of the ER by addition of 1 mM CaCl 2 to the extracellular medium until [Ca 2 þ ] in the ER lumen ([Ca 2 þ ] ER ) reaches steady state; and (iii) release of Ca 2 þ through Ca 2 þ leak or release channels 29,30 (see also Materials and Methods). The strategic advantage of this protocol was that it allowed us to analyze separately the three fundamental parameters of ER Ca 2 þ homeostasis, respectively: (i) Ca 2 þ accumulation into the ER, through the complex interplay between store-operated Ca 2 þ influx into the cell immediately followed by its transport into the ER lumen by sarcoendoplasmic reticulum Ca 2 þ -ATPase (SERCA); 31,32 (ii) steadystate ER luminal Ca 2 þ concentration ([Ca 2 þ ] ER ) determining Ca 2 þ -dependent folding and redox processes of the organelle 33,34 ; and (iii) the Ca 2 þ leak observed after inhibition of SERCA-mediated Ca 2 þ uptake by 2,5-di(t-butyl)-1,4-benzohydroquinone (tBHQ) 29 (Figure 7). Based on these data, we concluded that Ca 2 þ is a major regulator of CRT translocation.…”

Section: Rtn-1c and Mito Reduce Er Luminal [Camentioning

confidence: 99%

Reduction of endoplasmic reticulum Ca2+ levels favors plasma membrane surface exposure of calreticulin

et al. 2007

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Some chemotherapeutic agents can elicit apoptotic cancer cell death, thereby activating an anticancer immune response that influences therapeutic outcome. We previously reported that anthracyclins are particularly efficient in inducing immunogenic cell death, correlating with the pre-apoptotic exposure of calreticulin (CRT) on the plasma membrane surface of anthracyclintreated tumor cells. Here, we investigated the role of cellular Ca 2 þ homeostasis on CRT exposure. A neuroblastoma cell line (SH-SY5Y) failed to expose CRT in response to anthracyclin treatment. This defect in CRT exposure could be overcome by the overexpression of Reticulon-1C, a manipulation that led to a decrease in the Ca 2 þ concentration within the endoplasmic reticulum lumen. The combination of Reticulon-1C expression and anthracyclin treatment yielded more pronounced endoplasmic reticulum Ca 2 þ depletion than either of the two manipulations alone. Chelation of intracellular (and endoplasmic reticulum) Ca 2 þ , targeted expression of the ligand-binding domain of the IP 3 receptor and inhibition of the sarco-endoplasmic reticulum Ca 2 þ -ATPase pump reduced endoplasmic reticulum Ca 2 þ load and promoted pre-apoptotic CRT exposure on the cell surface, in SH-SY5Y and HeLa cells. These results provide evidence that endoplasmic reticulum Ca 2 þ levels control the exposure of CRT. In contrast to prior belief, apoptotic cell death can be immunogenic and hence elicits an active immune response against dying tumor cells. 1 This is therapeutically relevant because immune defects that compromise the response against apoptotic cells reduce the efficacy of anticancer chemotherapy, both in suitable animal models and in patients. 2 We found that anthracyclins and g-irradiation are particularly efficient in inducing immunogenic cell death, at least in mouse models. [3][4][5] The immunogenicity of cellular demise correlates with the exposure of calreticulin (CRT) on the plasma membrane (PM) surface of stressed tumor cells, a phenomenon that manifests before the cells acquire signs of apoptosis such as phosphatidylserine exposure. Inhibition of CRT exposure curtails the capacity of anthracyclin-treated or irradiated tumor cells to vaccinate against cancer and reduces the therapeutic efficacy of anthracyclins on tumors established in immunocompetent hosts. 3-5 Provision of recombinant CRT or drug-mediated enforcement of CRT exposure rendered per se nonimmunogenic chemotherapies (for instance with etoposide and mitomycin C) immunogenic and boosted their therapeutic efficacy. 5 These results suggest that CRT exposure is both necessary and sufficient to render conventional chemotherapies immunogenic.CRT is an abundant Ca 2 þ -binding chaperone that is mostly present in the endoplasmic reticulum (ER) lumen, although it can also be found in other subcellular localizations. 6,7 When present on the surface of damaged cells, it can serve as an 'eat-me' signal and hence facilitate the recognition and later engulfment of the dying cells by macrophages 8 or by dendrit...

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Beyond lectins: the calnexin/calreticulin chaperone system of the endoplasmic reticulum

Cited by 424 publications

References 102 publications

Protein Folding and Quality Control in the ER

Protein Folding and Quality Control in the ER

Human GGT2 Does Not Autocleave into a Functional Enzyme: A Cautionary Tale for Interpretation of Microarray Data on Redox Signaling

Reduction of endoplasmic reticulum Ca2+ levels favors plasma membrane surface exposure of calreticulin

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