Disease relevance of Calr

• The lack of specificity for calnexin interaction reveals a novel role for calreticulin in OCAI albinism [1].
• Complete heart block and sudden death in mice overexpressing calreticulin [2].
• Mice homozygous for the calreticulin gene disruption developed omphalocele (failure of absorption of the umbilical hernia) and showed a marked decrease in ventricular wall thickness and deep intertrabecular recesses in the ventricular walls [3].
• We have previously enhanced DNA vaccine potency by targeting antigen to MHC antigen presentation pathways, using proteins such as Mycobacterium tuberculosis heat shock protein 70, calreticulin, domain II of Pseudomonas aeruginosa exotoxin A, or the sorting signal of the lysosome-associated membrane protein type 1 [4].
• In an adoptive immunotherapy protocol, dendritic cells pulsed with calreticulin isolated from B16/F10.9 murine melanoma, E.G7-OVA, or EL4 thymoma tumors elicited a CTL response to as yet unknown tumor-derived Ags or the known OVA Ag [5].

High impact information on Calr

• Cell-surface calreticulin initiates clearance of viable or apoptotic cells through trans-activation of LRP on the phagocyte [6].
• These changes on the apoptotic cell create an environment where "don't eat me" signals are rendered inactive and "eat me" signals, including calreticulin and phosphatidylserine, congregate together and signal for removal [6].
• Blockade or knockdown of CRT suppressed the phagocytosis of anthracyclin-treated tumor cells by dendritic cells and abolished their immunogenicity in mice [7].
• Calreticulin exposure dictates the immunogenicity of cancer cell death [7].
• We have now developed calreticulin-deficient embryonic stem (ES) cells and isolated embryonic fibroblasts from calreticulin mutant mice [8].

Chemical compound and disease context of Calr

• Inhibition of retinoic acid receptor function and retinoic acid-regulated gene expression in mouse melanoma cells by calreticulin. A potential pathway for cyclic AMP regulation of retinoid action [9].
• Here we report that overexpression of the calreticulin gene in B16 mouse melanoma cells resulted in a decrease in retinoic acid (RA)-stimulated reporter gene expression [9].
• In the present study, we have immunocaptured a cell surface complex from B16 mouse melanoma cells which contains alpha 6 beta 1 integrin, two molecular forms of calreticulin, and KDEL docking protein (KDEL-R) [10].

Biological context of Calr

• Mapping of the gene for calreticulin (Calr) to mouse chromosome 8 [11].
• Therefore, the aim of this study was to investigate the role of CRT in the regulation of apoptosis via modulating p53 function and expression [12].
• Calreticulin is a Ca2+ -binding chaperone that resides in the lumen of the endoplasmic reticulum and is involved in the regulation of intracellular Ca2+ homeostasis and in the folding of newly synthesized glycoproteins [13].
• We conclude that mutation of a single amino acid residue in calreticulin has devastating consequences for its chaperone function, indicating that mutations in chaperones may play a significant role in protein folding disorders [14].
• The Cys(88) and Cys(120) mutants rescued the calreticulin-deficient phenotype only partially ( approximately 40%), and the Trp(244) and Trp(302) mutants did not rescue it at all [13].

Anatomical context of Calr

• Calreticulin and calnexin are homologous lectins that serve as molecular chaperones for glycoproteins in the endoplasmic reticulum of eukaryotic cells [15].
• Bradykinin-dependent Ca2+ release from the endoplasmic reticulum was rescued by wild-type calreticulin and by the Glu(238), Glu(239), Asp(241), and Glu(243) mutants [13].
• Calreticulin mutants were expressed in crt(-/-) fibroblasts, and bradykinin-dependent Ca2+ release was measured as a marker of calreticulin function [13].
• Calreticulin is a Ca(2+)-binding chaperone localized mainly in the endoplasmic/sarcoplasmic reticulum in all higher organisms [16].
• The gene encoding the novel human calreticulin isoform spans 17 kb of genomic DNA and is expressed in testis, showing a similar expression as the chaperone calmegin [16].

Associations of Calr with chemical compounds

• Although not fully interchangeable during assistance of glycoprotein folding, calreticulin and calnexin may work, independently, as efficient and crucial factors for retention in the ER of nonnative polypeptides [15].
• Bradykinin-dependent Ca2+ release from the ER was rescued by wild type calreticulin and by the His25, His82, or His128 mutant but not by the His153 mutant [14].
• Functional relationship between calreticulin, calnexin, and the endoplasmic reticulum luminal domain of calnexin [17].
• Identification of an N-domain histidine essential for chaperone function in calreticulin [14].
• Wild type calreticulin and the His25, His82, and His128 mutants all prevented in vitro thermal aggregation of malate dehydrogenase and IgY, whereas the His153 mutant did not, indicating that His153 chaperone function was impaired [14].

Physical interactions of Calr

• Conversely, membrane-anchored calreticulin bound to a similar set of glycoproteins as calnexin [17].
• Calreticulin exhibits the ability to inhibit DNA-binding activity of both heterodimeric RAR/RXR and homodimeric RXR complexes in vitro [18].
• Furthermore, K3 is detected predominantly in association with class I molecules lacking assembly with high-affinity peptides, including class I molecules associated with the peptide loading complex TAP/tapasin/calreticulin [19].
• Immunogenicity of calreticulin-bound murine leukemia virus glycoprotein gp90 [20].

Regulatory relationships of Calr

• These results, lead us to conclude that CRT regulates p53 function by affecting its rate of degradation and nuclear localization [12].
• PERK and Ire1alpha and eIF2alpha are also activated in calreticulin-deficient cells [21].
• RESULTS: We show here that the levels of N-cadherin are downregulated in calreticulin-deficient mouse embryonic hearts, which may lead to the disarray and wavy appearance of myofibrils in these mice, which we detected at all investigated stages of cardiac development [22].
• Here, using L fibroblast cell lines expressing different levels of calreticulin, we show that calreticulin plays a role in the control of cell adhesiveness via regulation of expression of vinculin, a cytoskeletal protein essential for cell-substratum and cell-cell attachments [23].
• Here we show that the transcription factor Nkx2.5 activates expression of the calreticulin gene in the heart [24].

Other interactions of Calr

• Calreticulin associated more abundantly with orphan calnexin substrates only in infected cells and preferentially with polypeptides of viral origin, showing stronger dependence of model viral glycoproteins on endoplasmic reticulum lectins [25].
• Here we show a significant decrease in both basal and DNA damage induced p53 functions in the CRT-deficient cells (crt-/-) [12].
• We identified four amino acid residues (Glu(239), Asp(241), Glu(243), and Trp(244)) at the hairpin tip of the P-domain that are critical in the formation of a complex between ERp57 and calreticulin [13].
• On the cell surface, GRP78, PDI and Crt associate with other proteins and form complexes of different sizes [26].
• Using a Drosophila expression system and the mouse class I histocompatibility molecule as a model glycoprotein, we found that calreticulin does possess apparent chaperone and quality control functions, enhancing class I folding and subunit assembly, stabilizing subunits, and impeding export of assembly intermediates from the ER [17].

Analytical, diagnostic and therapeutic context of Calr

• In this study, we have used site-specific mutagenesis to map amino acid residues that are critical in calreticulin function [13].
• Co-immunoprecipitation and pulse-chase analyses revealed similar kinetics of apo(a) interaction with CNX and CRT, peaking 15-30 min after apo(a) synthesis [27].
• In CTLs, however, calreticulin colocalizes with the lytic perforin to the lysosome-like secretory granules, as confirmed by double label immunofluorescence confocal microscopy [28].
• To understand the physiological function of calreticulin we used gene targeting to create a knockout mouse for calreticulin [3].
• Molecular cloning and expression of SmIrV1, a Schistosoma mansoni antigen with similarity to calnexin, calreticulin, and OvRal1 [29].

References