Betacellulin is a protein that in humans is encoded by the BTC gene located on chromosome 4 at locus 4q13-q21. [5] Betacellulin was initially identified as a mitogen. [6] Betacellulin, is a part of an Epidermal Growth Factor (EGF) family and functions as a ligand for the epidermal growth factor receptor (EGFR). The role of betacellulin as an EGF is manifested differently in various tissues, and it has a great effect on nitrogen signaling in retinal pigment epithelial cells and vascular smooth muscle cells. While many studies attest a role for betacellulin in the differentiation of pancreatic β-cells, the last decade witnessed the association of betacellulin with many additional biological processes, ranging from reproduction to the control of neural stem cells. [6] Betacellulin is a member of the EGF family of growth factors. It is synthesized primarily as a transmembrane precursor, which is then processed to mature molecule by proteolytic events.
As shown on figure 1, the secondary structure of the human betacellulin-2 has 6% helical (1 helices; 3 residues) 36% beta sheet (5 strands; 18 residues). The mRNA of betacellulin contains six exons in which is 2816 base-pair long. [6] The mRNA was translated into 178 amino acids, and different regions of the amino acid are responsible for different function. [6] The first 31 amino acids are responsible for the signal peptide (Figure 2, exon 1), the 32nd to 118th amino acids are responsible for the extracellular region (Figure 2, exon 2 and 3), the 65-105 amino acids are responsible for the EGF-like domain (Figure 2, exon 3), the transmembrane domain is from amino acids 119-139 (Figure 2, exon 4), the cytoplasmic tail is from amino acid 140-178 (Figure 2, exon 5). [6]
As a typical EGFR ligand, betacellulin is expressed by a variety of cell types and tissues, the post-translation of the betacellulin can ectodomain shedding, and the proteolytic release the soluble factors can bind and activate the homodimer or heterodimer of the ERBB receptors. The membrane-anchored form of the betacellulin can activate the epidermal growth factor receptor (EGFR). [7] Betacellulin stimulates the proliferation of retinal pigment epithelial and vascular smooth muscle cells but did not stimulate the growth of several other cell types, such as endothelial cells and fetal lung fibroblasts. [8]
The mRNA coding for betacellulin was found to be slightly higher compared in the rat sciatic nerve segment after nerve damage, suggesting that betacellulin can play a role in peripheral nerve regeneration. Immunohistochemistry has been used to look for betacellulin expression in Schwann cells. Treating cells with betacellulin recombinant protein can be used to investigate the role of betacellulin in managing Schwann cells. A co-culture assay can also used to assess the effect of Schwann cell-secreted betacellulin on neurons. [9]
Mouse BTC is expressed as a 178-amino acid precursor. The membrane-bound precursor is cleaved to yield mature secreted mouse BTC. BTC is synthesized in a wide range of adult tissues and in many cultured cells, including smooth muscle cells and epithelial cells. The amino acid sequence of mature mouse BTC is 82.5%, identical with that of human BTC, and both exhibit significant overall similarity with other members of the EGF family.
The transcription factor signal transducer and activator of transcription 3 (STAT3) was identified as the therapeutic target for glioblastoma. [10]
Epidermal growth factor (EGF) is a protein that stimulates cell growth and differentiation by binding to its receptor, EGFR. Human EGF is 6-kDa and has 53 amino acid residues and three intramolecular disulfide bonds.
The epidermal growth factor receptor is a transmembrane protein that is a receptor for members of the epidermal growth factor family of extracellular protein ligands.
Neuregulins are a family of four structurally related proteins that are part of the EGF family of proteins. These proteins have been shown to have diverse functions in the development of the nervous system and play multiple essential roles in vertebrate embryogenesis including: cardiac development, Schwann cell and oligodendrocyte differentiation, some aspects of neuronal development, as well as the formation of neuromuscular synapses.
Amphiregulin, also known as AREG, is a protein synthesized as a transmembrane glycoprotein with 252 aminoacids and it is encoded by the AREG gene. in humans.
Receptor tyrosine-protein kinase erbB-2 is a protein that normally resides in the membranes of cells and is encoded by the ERBB2 gene. ERBB is abbreviated from erythroblastic oncogene B, a gene originally isolated from the avian genome. The human protein is also frequently referred to as HER2 or CD340.
The MAPK/ERK pathway is a chain of proteins in the cell that communicates a signal from a receptor on the surface of the cell to the DNA in the nucleus of the cell.
Receptor tyrosine kinases (RTKs) are the high-affinity cell surface receptors for many polypeptide growth factors, cytokines, and hormones. Of the 90 unique tyrosine kinase genes identified in the human genome, 58 encode receptor tyrosine kinase proteins. Receptor tyrosine kinases have been shown not only to be key regulators of normal cellular processes but also to have a critical role in the development and progression of many types of cancer. Mutations in receptor tyrosine kinases lead to activation of a series of signalling cascades which have numerous effects on protein expression. Receptor tyrosine kinases are part of the larger family of protein tyrosine kinases, encompassing the receptor tyrosine kinase proteins which contain a transmembrane domain, as well as the non-receptor tyrosine kinases which do not possess transmembrane domains.
Transforming growth factor alpha (TGF-α) is a protein that in humans is encoded by the TGFA gene. As a member of the epidermal growth factor (EGF) family, TGF-α is a mitogenic polypeptide. The protein becomes activated when binding to receptors capable of protein kinase activity for cellular signaling.
Fibroblast growth factor receptor 1 (FGFR1), also known as basic fibroblast growth factor receptor 1, fms-related tyrosine kinase-2 / Pfeiffer syndrome, and CD331, is a receptor tyrosine kinase whose ligands are specific members of the fibroblast growth factor family. FGFR1 has been shown to be associated with Pfeiffer syndrome, and clonal eosinophilias.
The ErbB family of proteins contains four receptor tyrosine kinases, structurally related to the epidermal growth factor receptor (EGFR), its first discovered member. In humans, the family includes Her1, Her2 (ErbB2), Her3 (ErbB3), and Her4 (ErbB4). The gene symbol, ErbB, is derived from the name of a viral oncogene to which these receptors are homologous: erythroblastic leukemia viral oncogene. Insufficient ErbB signaling in humans is associated with the development of neurodegenerative diseases, such as multiple sclerosis and Alzheimer's disease, while excessive ErbB signaling is associated with the development of a wide variety of types of solid tumor.
Heparin-binding EGF-like growth factor (HB-EGF) is a member of the EGF family of proteins that in humans is encoded by the HBEGF gene.
Epiregulin (EPR) is a protein that in humans is encoded by the EREG gene.
Receptor tyrosine-protein kinase erbB-3, also known as HER3, is a membrane bound protein that in humans is encoded by the ERBB3 gene.
Receptor tyrosine-protein kinase erbB-4 is an enzyme that in humans is encoded by the ERBB4 gene. Alternatively spliced variants that encode different protein isoforms have been described; however, not all variants have been fully characterized.
CBL-B is an E3 ubiquitin-protein ligase that in humans is encoded by the CBLB gene. CBLB is a member of the CBL gene family.
Cadherin EGF LAG seven-pass G-type receptor 2 is a protein that in humans is encoded by the CELSR2 gene.
The EGF-like domain is an evolutionary conserved protein domain, which derives its name from the epidermal growth factor where it was first described. It comprises about 30 to 40 amino-acid residues and has been found in a large number of mostly animal proteins. Most occurrences of the EGF-like domain are found in the extracellular domain of membrane-bound proteins or in proteins known to be secreted. An exception to this is the prostaglandin-endoperoxide synthase. The EGF-like domain includes 6 cysteine residues which in the epidermal growth factor have been shown to form 3 disulfide bonds. The structures of 4-disulfide EGF-domains have been solved from the laminin and integrin proteins. The main structure of EGF-like domains is a two-stranded β-sheet followed by a loop to a short C-terminal, two-stranded β-sheet. These two β-sheets are usually denoted as the major (N-terminal) and minor (C-terminal) sheets. EGF-like domains frequently occur in numerous tandem copies in proteins: these repeats typically fold together to form a single, linear solenoid domain block as a functional unit.
ERBB receptor feedback inhibitor 1 is a protein that in humans is encoded by the ERRFI1 gene.
Potato carboxypeptidase inhibitor (PCI) is a naturally occurring protease inhibitor peptide in potatoes that can form complexes with several metallo-carboxypeptidases, inhibiting them in a strong competitive way with a Ki in the nanomolar range.
PCI consists of 39 amino acids forming a 27-residue globular core stabilized by three disulfide bridges and a C-terminal tail with residues 35–39. PCI contains a small cysteine-rich module, called a T-knot scaffold, that is shared by several different protein families, including the EGF family.
Megf8 also known as Multiple Epidermal Growth Factor-like Domains 8, is a protein coding gene that encodes a single pass membrane protein, known to participate in developmental regulation and cellular communication. It is located on chromosome 19 at the 49th open reading frame in humans (19q13.2). There are two isoform constructs known for MEGF8, which differ by a 67 amino acid indel. The isoform 2 splice version is 2785 amino acids long, and predicted to be 296.6 kdal in mass. Isoform 1 is composed of 2845 amino acids and predicted to weigh 303.1 kdal. Using BLAST searches, orthologs were found primarily in mammals, but MEGF8 is also conserved in invertebrates and fishes, and rarely in birds, reptiles, and amphibians. A notably important paralog to multiple epidermal growth factor-like domains 8 is ATRNL1, which is also a single pass transmembrane protein, with several of the same key features and motifs as MEGF8, as indicated by Simple Modular Architecture Research Tool (SMART) which is hosted by the European Molecular Biology Laboratory located in Heidelberg, Germany. MEGF8 has been predicted to be a key player in several developmental processes, such as left-right patterning and limb formation. Currently, researchers have found MEGF8 SNP mutations to be the cause of Carpenter syndrome subtype 2.
This article incorporates text from the United States National Library of Medicine, which is in the public domain.