Cysteine-rich with EGF-like domain protein 2 is a protein that in humans is encoded by the CRELD2 gene found on chromosome 22q13. [1] [2] It is a known homolog of CRELD1. [3] CRELD2's identifying feature is a tryptophan-aspartic acid domain. [4] It is a multifunctional glycoprotein that is approximately 60 kilodaltons and can reside in the endoplasmic reticulum (ER) or Golgi apparatus and be secreted spontaneously. [3] It is implicated in numerous ER stress-related diseases including chronic liver disease, cardiovascular disease, kidney disease, and cancer. [5] [6]
CRELD2 can present itself in a variety of isoforms with similar motifs but different functions. [7] . Common motifs include EGF/calcium binding EGF domains and furin cysteine-rich domains. [3] The C-terminal of this protein includes the following specific amino acid sequence necessary for retention and secretion: (R/H)EDL. [8] The N-terminal has multiple CXXC motifs which are vital for translocation and isomerase activity. [4] CpG islands are present in the functional promoter region upstream of CRELD2. In this functional promoter region, GC nucleotides are abundant and a TATA box is absent. [7] An ERSE (ER Stress Responsible Element) is also present in CRELD2 and is conserved in numerous species. [3]
The CXXC motif at the N-terminal of CRELD2 suggests that it plays a role in the quality control of ER proteins. At the C-terminal, the four amino acids (R/H)EDL modulate the secretion of CRELD2. CRELD2 can bind to KDEL receptors in the Golgi and be retrogradely transported to the ER. [9] The presence of ER Stress Responsible Elements implies a regulatory role of CRELD2 during ER stress. [10] CRELD2 may function to promote ER stress tolerance or assist in recovery from acute stress. [11] The CRELD family is also implicated in developmental events. [7]
Throughout the life span of an individual, CRELD2 displays ubiquitous expression. Expression of CRELD2 is found in most, if not all, tissues including: skeletal muscle, heart, liver, kidney, and placenta. [12] The expression of CRELD2 differs in adult tissue and fetal tissue. In adult tissue, CRELD2 is mainly expressed in pancreatic tissue, stomach tissue, duodenal tissue, salivary gland tissue, thyroid gland tissue, appendix tissue, and tracheal tissue. Fetal expression of CRELD2 occurs primarily in the following tissues: lung, liver, thymus, spleen, and heart. Expression of CRELD2 can be induced by inducing ER stress via chemicals such as Tm, Tg, and BFA.
In adult mice, exposure to arsenic during gestation led to high levels of CRELD2 expression in the liver. Expression of CRELD2 in the livers of mice also increased following 24 hours of intraperitoneal Tm infusion. Furthermore, in older mice with a knockout for Grp78, alcohol resulted in an increase of methylation at CpG islands in genes involved in CRELD2 expression. [13] Based on these studies utilizing mice models, CRELD2 is implicated in maintenance of liver homeostasis. [11]
CRELD2 has been highly implicated in chronic vascular diseases based on multiple studies. In cardiomyocytes of neonatal rats, administration of Tm led to increased levels of CRELD2 mRNA. When an ER-stress inhibitor, salubrinal, was administered, the observed effect was reversed. [14] In another study, the aortic zone exhibited elevated CRELD2 expression which confirmed the presence of a mutation in the 3’ untranslated region of FBN1 and associated ER stress response. Furthermore, aneurysmal samples from humans displayed high levels of CRELD2. [15]
CRELD is implicated in the homeostasis of cartilage and bone development based on numerous examples. In a mutant Matn3 model of multiple epiphyseal dysplasia, CRELD2 was found to be expressed at the highest levels in chondrocytes. [16] In mouse models of ER-stress related growth plate diseases, CRELD2 expression was observed in hypertrophic zones. In addition, when ER stress was induced in cartilage treated with interleukin-1alpha, CRELD2 involvement was observed. Moreover, during osteogenic differentiation of mesenchymal stem cells mediated via bone morphogenic protein 9, CRELD2 displays high levels of up-regulation. [17] [18] [19] [20] [21]
ER stress, and thus CRELD2, are associated with the development of numerous types of cancer and tumor progression. Tumor angiogenesis can be promoted by CRELD2 up-regulating MB114 cell invasion. Additionally, CRELD2 was implicated as target of androgen receptors in prostate cancer. In renal cell carcinoma patients, CRELD2 expression was correlated with a poor prognosis. Furthermore, the presence of the CRELD2 gene and expression of the CRELD2 protein was linked to decreased chances of disease-free survival in cases of hepatocellular carcinoma. Another example implication the role of CRELD2 in cancer is exhibited in breast cancer. [22] Tumor progression was promoted by high levels of CRELD2, while lack of adequate CRELD2 expression suppressed tumor growth. [23]
Due to its association with ER stress, CRELD2 can be utilized as a biomarker in ER-stress related diseases. For example, prosthetic joint infection can be detected via the presence of CRELD2 in synovial fluid. [24] Also, in males with NASH, decreased serum CRELD2 concentration led to higher levels of disease progression. Lastly, CRELD2 in the urine can be used as a biomarker for ER-stress related kidney diseases.
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.
Protein disulfide isomerase, or PDI, is an enzyme in the endoplasmic reticulum (ER) in eukaryotes and the periplasm of bacteria that catalyzes the formation and breakage of disulfide bonds between cysteine residues within proteins as they fold. This allows proteins to quickly find the correct arrangement of disulfide bonds in their fully folded state, and therefore the enzyme acts to catalyze protein folding.
In cellular biology, the Wnt signaling pathways are a group of signal transduction pathways which begin with proteins that pass signals into a cell through cell surface receptors. The name Wnt is a portmanteau created from the names Wingless and Int-1. Wnt signaling pathways use either nearby cell-cell communication (paracrine) or same-cell communication (autocrine). They are highly evolutionarily conserved in animals, which means they are similar across animal species from fruit flies to humans.
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.
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.
Activating transcription factor 6, also known as ATF6, is a protein that, in humans, is encoded by the ATF6 gene and is involved in the unfolded protein response.
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.
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.
Insulin induced gene 1, also known as INSIG1, is a protein which in humans is encoded by the INSIG1 gene.
The serine/threonine-protein kinase/endoribonuclease inositol-requiring enzyme 1 α (IRE1α) is an enzyme that in humans is encoded by the ERN1 gene.
Nuclear factor erythroid 2-related factor 1 (Nrf1) also known as nuclear factor erythroid-2-like 1 (NFE2L1) is a protein that in humans is encoded by the NFE2L1 gene. Since NFE2L1 is referred to as Nrf1, it is often confused with nuclear respiratory factor 1 (Nrf1).
Derlin-1 also known as degradation in endoplasmic reticulum protein 1 is a membrane protein that in humans is encoded by the DERL1 gene. Derlin-1 is located in the membrane of the endoplasmic reticulum (ER) and is involved in retrotranslocation of specific misfolded proteins and in ER stress. Derlin-1 is widely expressed in thyroid, fat, bone marrow and many other tissues. The protein belongs to the Derlin-family proteins consisting of derlin-1, derlin-2 and derlin-3 that are components in the endoplasmic reticulum-associated protein degradation (ERAD) pathway. The derlins mediate degradation of misfolded lumenal proteins within ER, and are named ‘der’ for their ‘Degradation in the ER’. Derlin-1 is a mammalian homologue of the yeast DER1 protein, a protein involved in the yeast ERAD pathway. Moreover, derlin-1 is a member of the rhomboid-like clan of polytopic membrane proteins.
Zinc transporter SLC39A7 (ZIP7), also known as solute carrier family 39 member 7, is a transmembrane protein that in humans is encoded by the SLC39A7 gene. It belongs to the ZIP family, which consists of 14 proteins that transport zinc into the cytoplasm. Its primary role is to control the transport of zinc from the ER and Golgi apparatus to the cytoplasm. It also plays a role in glucose metabolism. Its structure consists of helices that bind to zinc in a binuclear metal center. Its fruit fly orthologue is Catsup.
Matrix metallopeptidase 27 also known as MMP-27 is an enzyme which in humans is encoded by the MMP27 gene.
Proteostasis is the dynamic regulation of a balanced, functional proteome. The proteostasis network includes competing and integrated biological pathways within cells that control the biogenesis, folding, trafficking, and degradation of proteins present within and outside the cell. Loss of proteostasis is central to understanding the cause of diseases associated with excessive protein misfolding and degradation leading to loss-of-function phenotypes, as well as aggregation-associated degenerative disorders. Therapeutic restoration of proteostasis may treat or resolve these pathologies.
O-linked glycosylation is the attachment of a sugar molecule to the oxygen atom of serine (Ser) or threonine (Thr) residues in a protein. O-glycosylation is a post-translational modification that occurs after the protein has been synthesised. In eukaryotes, it occurs in the endoplasmic reticulum, Golgi apparatus and occasionally in the cytoplasm; in prokaryotes, it occurs in the cytoplasm. Several different sugars can be added to the serine or threonine, and they affect the protein in different ways by changing protein stability and regulating protein activity. O-glycans, which are the sugars added to the serine or threonine, have numerous functions throughout the body, including trafficking of cells in the immune system, allowing recognition of foreign material, controlling cell metabolism and providing cartilage and tendon flexibility. Because of the many functions they have, changes in O-glycosylation are important in many diseases including cancer, diabetes and Alzheimer's. O-glycosylation occurs in all domains of life, including eukaryotes, archaea and a number of pathogenic bacteria including Burkholderia cenocepacia, Neisseria gonorrhoeae and Acinetobacter baumannii.
Cellular stress response is the wide range of molecular changes that cells undergo in response to environmental stressors, including extremes of temperature, exposure to toxins, and mechanical damage. Cellular stress responses can also be caused by some viral infections. The various processes involved in cellular stress responses serve the adaptive purpose of protecting a cell against unfavorable environmental conditions, both through short term mechanisms that minimize acute damage to the cell's overall integrity, and through longer term mechanisms which provide the cell a measure of resiliency against similar adverse conditions.
Melanoma inhibitory activity protein 3 (MIA3), also known as transport and Golgi organization protein 1 (TANGO1), is a protein that in humans is encoded by the MIA3 gene on chromosome 1. It is ubiquitously expressed in many tissues and cell types. MIA3 localizes to the endoplasmic reticulum (ER) exit site, where it binds bulky cargo molecules such as collagens and creates mega transport carriers for the export of cargoes from the ER. This function suggests that it plays a role in assembly of extracellular matrix (ECM) and bone formation. MIA3 has been demonstrated to contribute to both tumor suppression and progression. The MIA3 gene also contains one of 27 loci associated with increased risk of coronary artery disease.. A TANGO1 like protein called TALI is expressed in liver and intestine and shown to be required for the export of bulky very Low density lipoproteins (VLDL) and chylomicrons. TANGO1 and TALI assemble into rings around COPII coats and this function is necessary for export of bulky cargoes. The discovery of TANGO1 and understanding its function has revealed that cargo export from the ER is not be vesicles but involves transient tunnels between the ER exit site and the next compartment of the secretory pathway. Biallelic Mutations in TANGO1 cause syndrome disease and complete loss of TANGO1 leads of defects in bone mineralization. These findings highlight the significance of TANGO1 in building and ER exit site, controlling the quantities and quality of cargo exported, which is necessary for life.Membrane permeant peptides of TANGO1 affect hyper collagen secretion in normal and cells of patients with scleroderma, and in a zebra fish model of wound healing. These findings raise the possibility of targeting TANGO1 to control skin scarring, wound healing and fibrosis.
The endoplasmic reticulum membrane protein complex (EMC) is a putative endoplasmic reticulum-resident membrane protein (co-)chaperone. The EMC is evolutionarily conserved in eukaryotes, and its initial appearance might reach back to the last eukaryotic common ancestor (LECA). Many aspects of mEMC biology and molecular function remain to be studied.
cIAP1 is the abbreviation for a human protein, cellular inhibitor of apoptosis protein-1. It belongs to the IAP family of proteins and therefore contains at least one BIR domain. cIAP1 is a multi-functional protein which can be found in the cytoplasm of cells and in the nucleus of tumor cells. Its function in this particular case is yet to be understood. However, it is well known that this protein has a big influence in the growth of diverse cancers. cIAP1 is involved in the development process of osteosarcoma and gastric cancer among others.