Calreticulin

Last updated

CALR
Protein CALR PDB 1hhn.png
Available structures
PDB Ortholog search: PDBe RCSB
Identifiers
Aliases CALR , CRT, HEL-S-99n, RO, SSA, cC1qR, calreticulin
External IDs OMIM: 109091; MGI: 88252; HomoloGene: 37911; GeneCards: CALR; OMA:CALR - orthologs
Orthologs
SpeciesHumanMouse
Entrez
Ensembl
UniProt
RefSeq (mRNA)

NM_004343

NM_007591

RefSeq (protein)

NP_004334

NP_031617

Location (UCSC) Chr 19: 12.94 – 12.94 Mb Chr 8: 85.57 – 85.57 Mb
PubMed search [3] [4]
Wikidata
View/Edit Human View/Edit Mouse

Calreticulin also known as calregulin, CRP55, CaBP3, calsequestrin-like protein, and endoplasmic reticulum resident protein 60 (ERp60) is a protein that in humans is encoded by the CALR gene. [5] [6]

Contents

Calreticulin is a multifunctional soluble protein that binds Ca2+ ions (a second messenger in signal transduction), rendering them inactive. The Ca2+ is bound with low affinity, but high capacity, and can be released on a signal (see inositol trisphosphate). Calreticulin is located in storage compartments associated with the endoplasmic reticulum and is considered an ER resident protein. [6]

The term "Mobilferrin" [7] is considered to be the same as calreticulin by some sources. [8]

Function

Calreticulin binds to misfolded proteins and prevents them from being exported from the endoplasmic reticulum to the Golgi apparatus.

A similar quality-control molecular chaperone, calnexin, performs the same service for soluble proteins as does calreticulin, however it is a membrane-bound protein. Both proteins, calnexin and calreticulin, have the function of binding to oligosaccharides containing terminal glucose residues, thereby targeting them for degradation. Calreticulin and Calnexin's ability to bind carbohydrates associates them with the lectin protein family. In normal cellular function, trimming of glucose residues off the core oligosaccharide added during N-linked glycosylation is a part of protein processing. If "overseer" enzymes note that residues are misfolded, proteins within the rER will re-add glucose residues so that other calreticulin/calnexin can bind to these proteins and prevent them from proceeding to the Golgi. This leads these aberrantly folded proteins down a path whereby they are targeted for degradation.

Studies on transgenic mice reveal that calreticulin is a cardiac embryonic gene that is essential during development. [9]

Calreticulin and calnexin are also integral in the production of MHC class I proteins. As newly synthesized MHC class I α-chains enter the endoplasmic reticulum, calnexin binds on to them retaining them in a partly folded state. [10] After the β2-microglobulin binds to the peptide-loading complex (PLC), calreticulin (along with ERp57) takes over the job of chaperoning the MHC class I protein while the tapasin links the complex to the transporter associated with antigen processing (TAP) complex. This association prepares the MHC class I to bind an antigen for presentation on the cell surface.

Transcription regulation

Calreticulin is also found in the nucleus, suggesting that it may have a role in transcription regulation. Calreticulin binds to the synthetic peptide KLGFFKR, which is almost identical to an amino acid sequence in the DNA-binding domain of the superfamily of nuclear receptors. The amino terminus of calreticulin interacts with the DNA-binding domain of the glucocorticoid receptor and prevents the receptor from binding to its specific glucocorticoid response element. Calreticulin can inhibit the binding of androgen receptor to its hormone-responsive DNA element and can inhibit androgen receptor and retinoic acid receptor transcriptional activities in vivo, as well as retinoic acid-induced neuronal differentiation. Thus, calreticulin can act as an important modulator of the regulation of gene transcription by nuclear hormone receptors.

Clinical significance

Calreticulin binds to antibodies in certain area of systemic lupus and Sjögren patients that contain anti-Ro/SSA antibodies. Systemic lupus erythematosus is associated with increased autoantibody titers against calreticulin, but calreticulin is not a Ro/SS-A antigen. Earlier papers referred to calreticulin as an Ro/SS-A antigen, but this was later disproven. Increased autoantibody titer against human calreticulin is found in infants with complete congenital heart block of both the IgG and IgM classes. [11]

In 2013, two groups detected calreticulin mutations in a majority of JAK2-negative/MPL-negative patients with essential thrombocythemia and primary myelofibrosis, which makes CALR mutations the second most common in myeloproliferative neoplasms. All mutations (insertions or deletions) affected the last exon, generating a reading frame shift of the resulting protein, that creates a novel terminal peptide and causes a loss of endoplasmic reticulum KDEL retention signal. [12] [13]

Role in cancer

Calreticulin (CRT) is expressed in many cancer cells and plays a role to promote macrophages to engulf hazardous cancerous cells. The reason why most of the cells are not destroyed is the presence of another molecule with signal CD47, which blocks CRT. Hence antibodies that block CD47 might be useful as a cancer treatment. In mice models of myeloid leukemia and non-Hodgkin lymphoma, anti-CD47 were effective in clearing cancer cells while normal cells were unaffected. [14]

Interactions

Calreticulin has been shown to interact with Perforin [15] and NK2 homeobox 1. [16]

Related Research Articles

<span class="mw-page-title-main">Endoplasmic reticulum</span> Cell organelle that synthesizes, folds and processes proteins

The endoplasmic reticulum (ER) is a part of a transportation system of the eukaryotic cell, and has many other important functions such as protein folding. It is a type of organelle made up of two subunits – rough endoplasmic reticulum (RER), and smooth endoplasmic reticulum (SER). The endoplasmic reticulum is found in most eukaryotic cells and forms an interconnected network of flattened, membrane-enclosed sacs known as cisternae, and tubular structures in the SER. The membranes of the ER are continuous with the outer nuclear membrane. The endoplasmic reticulum is not found in red blood cells, or spermatozoa.

<span class="mw-page-title-main">Essential thrombocythemia</span> Overproduction of platelets in the bone marrow

In hematology, essential thrombocythemia (ET) is a rare chronic blood cancer characterised by the overproduction of platelets (thrombocytes) by megakaryocytes in the bone marrow. It may, albeit rarely, develop into acute myeloid leukemia or myelofibrosis. It is one of the blood cancers wherein the bone marrow produces too many white or red blood cells, or platelets.

<span class="mw-page-title-main">MHC class I</span> Protein of the immune system

MHC class I molecules are one of two primary classes of major histocompatibility complex (MHC) molecules and are found on the cell surface of all nucleated cells in the bodies of vertebrates. They also occur on platelets, but not on red blood cells. Their function is to display peptide fragments of proteins from within the cell to cytotoxic T cells; this will trigger an immediate response from the immune system against a particular non-self antigen displayed with the help of an MHC class I protein. Because MHC class I molecules present peptides derived from cytosolic proteins, the pathway of MHC class I presentation is often called cytosolic or endogenous pathway.

<span class="mw-page-title-main">LDL receptor</span> Mammalian protein found in Homo sapiens

The low-density lipoprotein receptor (LDL-R) is a mosaic protein of 839 amino acids that mediates the endocytosis of cholesterol-rich low-density lipoprotein (LDL). It is a cell-surface receptor that recognizes apolipoprotein B100 (ApoB100), which is embedded in the outer phospholipid layer of very low-density lipoprotein (VLDL), their remnants—i.e. intermediate-density lipoprotein (IDL), and LDL particles. The receptor also recognizes apolipoprotein E (ApoE) which is found in chylomicron remnants and IDL. In humans, the LDL receptor protein is encoded by the LDLR gene on chromosome 19. It belongs to the low density lipoprotein receptor gene family. It is most significantly expressed in bronchial epithelial cells and adrenal gland and cortex tissue.

<span class="mw-page-title-main">Calnexin</span> Mammalian protein found in humans

Calnexin (CNX) is a 67kDa integral protein of the endoplasmic reticulum (ER). It consists of a large N-terminal calcium-binding lumenal domain, a single transmembrane helix and a short, acidic cytoplasmic tail. In humans, calnexin is encoded by the gene CANX.

<span class="mw-page-title-main">Calcitonin receptor</span> Protein found in humans

The calcitonin receptor (CT) is a G protein-coupled receptor that binds the peptide hormone calcitonin and is involved in maintenance of calcium homeostasis, particularly with respect to bone formation and metabolism.

The unfolded protein response (UPR) is a cellular stress response related to the endoplasmic reticulum (ER) stress. It has been found to be conserved between mammalian species, as well as yeast and worm organisms.

<span class="mw-page-title-main">PDIA3</span> Protein-coding gene in the species Homo sapiens

Protein disulfide-isomerase A3 (PDIA3), also known as glucose-regulated protein, 58-kD (GRP58), is an isomerase enzyme encoded by the autosomal gene PDIA3 in humans. This protein localizes to the endoplasmic reticulum (ER) and interacts with lectin chaperones calreticulin and calnexin (CNX) to modulate folding of newly synthesized glycoproteins. It is thought that complexes of lectins and this protein mediate protein folding by promoting formation of disulfide bonds in their glycoprotein substrates.

<span class="mw-page-title-main">Ryanodine receptor 2</span> Transport protein and coding gene in humans

Ryanodine receptor 2 (RYR2) is one of a class of ryanodine receptors and a protein found primarily in cardiac muscle. In humans, it is encoded by the RYR2 gene. In the process of cardiac calcium-induced calcium release, RYR2 is the major mediator for sarcoplasmic release of stored calcium ions.

<span class="mw-page-title-main">HSP90B1</span> Protein-coding gene in the species Homo sapiens

Heat shock protein 90kDa beta member 1 (HSP90B1), known also as endoplasmin, gp96, grp94, or ERp99, is a chaperone protein that in humans is encoded by the HSP90B1 gene.

<span class="mw-page-title-main">XBP1</span> Protein-coding gene in the species Homo sapiens

X-box binding protein 1, also known as XBP1, is a protein which in humans is encoded by the XBP1 gene. The XBP1 gene is located on chromosome 22 while a closely related pseudogene has been identified and localized to chromosome 5. The XBP1 protein is a transcription factor that regulates the expression of genes important to the proper functioning of the immune system and in the cellular stress response.

<span class="mw-page-title-main">PPIB</span> Protein-coding gene in the species Homo sapiens

Peptidyl-prolyl cis-trans isomerase B is an enzyme that is encoded by the PPIB gene. As a member of the peptidyl-prolyl cis-trans isomerase (PPIase) family, this protein catalyzes the cis-trans isomerization of proline imidic peptide bonds, which allows it to regulate protein folding of type I collagen. Generally, PPIases are found in all eubacteria and eukaryotes, as well as in a few archaebacteria, and thus are highly conserved.

<span class="mw-page-title-main">Binding immunoglobulin protein</span> Protein-coding gene in the species Homo sapiens

Binding immunoglobulin protein (BiPS) also known as 78 kDa glucose-regulated protein (GRP-78) or heat shock 70 kDa protein 5 (HSPA5) is a protein that in humans is encoded by the HSPA5 gene.

<span class="mw-page-title-main">DNA damage-inducible transcript 3</span> Human protein and coding gene

DNA damage-inducible transcript 3, also known as C/EBP homologous protein (CHOP), is a pro-apoptotic transcription factor that is encoded by the DDIT3 gene. It is a member of the CCAAT/enhancer-binding protein (C/EBP) family of DNA-binding transcription factors. The protein functions as a dominant-negative inhibitor by forming heterodimers with other C/EBP members, preventing their DNA binding activity. The protein is implicated in adipogenesis and erythropoiesis and has an important role in the cell's stress response.

<span class="mw-page-title-main">BCAP31</span> Protein-coding gene in humans

B-cell receptor-associated protein 31 is a protein that in humans is encoded by the BCAP31 gene.

<span class="mw-page-title-main">KDELR1</span> Protein-coding gene in the species Homo sapiens

KDEL (Lys-Asp-Glu-Leu) endoplasmic reticulum protein retention receptor 1, also known as KDELR1, is a protein which in humans is encoded by the KDELR1 gene.

<span class="mw-page-title-main">Leukocyte receptor tyrosine kinase</span> Enzyme found in humans

Leukocyte receptor tyrosine kinase is an enzyme that in humans is encoded by the LTK gene.

<span class="mw-page-title-main">RRBP1</span> Protein-coding gene in the species Homo sapiens

Ribosome-binding protein 1, also referred to as p180, is a protein that in humans is encoded by the RRBP1 gene.

<span class="mw-page-title-main">Calreticulin protein family</span> Family of calcium-binding proteins

In molecular biology, the calreticulin protein family is a family of calcium-binding proteins. This family includes calreticulin, calnexin and camlegin.

<span class="mw-page-title-main">Peptide loading complex</span>

The peptide-loading complex (PLC) is a short-lived, multisubunit membrane protein complex that is located in the endoplasmic reticulum (ER). It orchestrates peptide translocation and selection by major histocompatibility complex class I (MHC-I) molecules. Stable peptide-MHC I complexes are released to the cell surface to promote T-cell response against malignant or infected cells. In turn, T-cells recognize the activated peptides, which could be immunogenic or non-immunogenic.

References

  1. 1 2 3 GRCh38: Ensembl release 89: ENSG00000179218 Ensembl, May 2017
  2. 1 2 3 GRCm38: Ensembl release 89: ENSMUSG00000003814 Ensembl, May 2017
  3. "Human PubMed Reference:". National Center for Biotechnology Information, U.S. National Library of Medicine.
  4. "Mouse PubMed Reference:". National Center for Biotechnology Information, U.S. National Library of Medicine.
  5. McCauliffe DP, Zappi E, Lieu TS, Michalak M, Sontheimer RD, Capra JD (Jul 1990). "A human Ro/SS-A autoantigen is the homologue of calreticulin and is highly homologous with onchocercal RAL-1 antigen and an aplysia "memory molecule"". The Journal of Clinical Investigation. 86 (1): 332–5. doi:10.1172/JCI114704. PMC   296725 . PMID   2365822.
  6. 1 2 "Entrez Gene: calreticulin".
  7. Mobilferrin at the U.S. National Library of Medicine Medical Subject Headings (MeSH)
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  10. Murphy K (2011). Janeway's Immunobiology (8th ed.). Oxford: Taylor & Francis. ISBN   978-0815342434.
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  13. Klampfl T, Gisslinger H, Harutyunyan AS, Nivarthi H, Rumi E, Milosevic JD, Them NC, Berg T, Gisslinger B, Pietra D, Chen D, Vladimer GI, Bagienski K, Milanesi C, Casetti IC, Sant'Antonio E, Ferretti V, Elena C, Schischlik F, Cleary C, Six M, Schalling M, Schönegger A, Bock C, Malcovati L, Pascutto C, Superti-Furga G, Cazzola M, Kralovics R (Dec 2013). "Somatic mutations of calreticulin in myeloproliferative neoplasms". The New England Journal of Medicine. 369 (25): 2379–90. doi: 10.1056/NEJMoa1311347 . PMID   24325356.
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Further reading