SHC-transforming protein 1 is a protein that in humans is encoded by the SHC1 gene. [5] SHC has been found to be important in the regulation of apoptosis and drug resistance in mammalian cells.
SCOP classifies the 3D structure as belonging to the SH2 domain family.
The gene SHC1 is located on chromosome 1 and encodes 3 main protein isoforms: p66SHC, p52SHC and p46SHC. These proteins differ in activity and subcellular locations, p66 is the longest and while the p52 and p46 link activated receptor tyrosine kinase to the RAS pathway. [6] The protein SHC1 also acts as a scaffold protein which is used in cell surface receptors. [7] The three proteins that SHC1 codes for have distinctly different molecular weights. [8] All three SHC1 proteins share the same domain arrangement consisting of an N-terminal phosphotyrosine-binding(PTB) domain and a C-terminal Src-homology2(SH2) domain. Both of the domains for the three proteins can bind to tyrosine-phosphorylated proteins but they are different in their phosphopeptide-binding specificities. [9] P66SHC is characterized by having an additional N-terminal CH2 domain. [9]
Overexpression of SHC proteins are associated with cancer mitogenesis, carcinogenesis and metastasis. [8] The SHC and its adaptor proteins transmit signaling of the cell surface receptors such as EGFR, erbV-2 and insulin receptors. p52SHC and p46SHC activate the Ras-ERK pathway. p66SHC inhibits ERK1/2 activity and antagonize mitogenic and survival abilities of T-lymphoma Jurkat cell lines. [8] A rise in p66SHC promotes stress induced apoptosis. [8] p66SHC functionally is also involved in regulating oxidative and stress- induced apoptosis – mediating steroid action through the redox signaling pathway. P52SHC and p66SHC have been found in steroid hormone-regulated cancer and metastasizes. [8]
SHC1 has been found to act in signaling information after epidermal growth factor (EGF) stimulation. Activated tyrosine kinase receptors, on the cell surface, use proteins such as SHC1 that contain phosphotyrosine binding domains. After the EGF stimulation SHC1 binds to groups of proteins that activate survival pathways. This activation is followed by a sub-network of proteins that bind to SHC1 and are involved cytoskeleton reorganization, trafficking and signal termination. PTPN122 then acts as a switch to convert SHC1 to SgK269-mediated pathways that regulate cell invasion and morphogenesis. [7] SHC1 is not a static scaffold protein, a protein that does not move or change over time, it is dynamic as the conformation changes and modifies the EGFR signaling output over time. [10]
SHC proteins are differentially regulated by the Multiple Copies in T-cell malignancy(MCT-1). This regulation affects the SHC-Ras-ERK pathway. [8] With MCT-1 reduction the phosphor activation of Ras, MEK and ERk ½ were also reduced, this reduction in ERK also affects cyclin D1. The expression of the SHC proteins (all three) were also dramatically reduced with the reduction of MCT-1 because of this it is thought that MCT-1 acts as an inducer of SHC gene transcription. p66SHC is found to be the protein that is most affected by MCT-1. SHC expression downregulated in tumorigenic processes are identified after MCT-1 depletion. By blocking the MCT-1 activity this could inhibit the SHC signaling cascase and the oncogenicty and tumorigenicity that is regulated by SHC expression. [8]
Oxidative stress occurs when the production of reactive oxygen species (ROS) is greater than their catabolism. ROS production by the mitochondria is regulated by many diverse factors including SHC1. [11] The SHC proteins are regulated by tyrosine phosphorylation and are part of the growth factor and stress-induced ERK activation. There have been findings that suggest a correlation between life span and the oxidative stress response. Selective resistance to oxidative stress and extended life span have been related to p66SHC. [12]
There is a link between oxidative stress, life span and p66SHC [12] in mice because of this relationship the SHC gene has been related to longevity and increasing the life span of the mouse. [13] It has been proposed that SHC1 modulates the life span and stress response through the DAF-2 insulin- like receptor of the IIS pathway. The SHC-1 can directly interact with the DAF-2 in vitro. [9]
p66SHC operates as a redox enzyme linked to apoptotic cell death. p66SHC has been related to the sirtuin-1 system and has been associated with endothelial damage and repair. This relationships is also related to vascular homeostasis and oxidative stress. [14] p66SHC can be altered by changes in the glucose metabolism and vascular senescence. When protein kinase C is induced by hyperglycemia, p66SHC is induced which then leads to oxidative stress. When the coagulated protease-activated protein C inhibits p66SHC a cytoprotective effect on diabetic nephropathy is placed on the kidneys . When a mutations such as a p66SHC deletion occurs the cardiomyocyte death is reduced and a pool of cardiac stem cells are preserved from oxidative damage – preventing diabetic cardiomyopathy. The deletion of p66SHC also protects from ischemia/reperfusion brain injuries through blunted production of free radicals. [14]
The signaling activation of SHC is implicated in tumorigenic in cancer cells there is a potential to use SHC as a prognostic marker when targeting cancer treatment. [8] SHC1 interacts with SgK269 which is a member of the Src kinase signaling network that characterized basal breast cancer cells. When SgK269 is overexpressed in mammary epithelial cells it promotes the cell growth and might contribute to the progression of aggressive breast cancers. [15] In prostate and ovarian cancer, increased expression of p66Shc appears to promote cell proliferation. [16] and tumorigenicity, particularly in prostate cancer xenografts [17] This tumorigenic effect is related to its ability to increase redox stress in these cancer cells. [18]
An oncogene is a gene that has the potential to cause cancer. In tumor cells, these genes are often mutated, or expressed at high levels.
A protein kinase is a kinase which selectively modifies other proteins by covalently adding phosphates to them (phosphorylation) as opposed to kinases which modify lipids, carbohydrates, or other molecules. Phosphorylation usually results in a functional change of the target protein (substrate) by changing enzyme activity, cellular location, or association with other proteins. The human genome contains about 500 protein kinase genes and they constitute about 2% of all human genes. There are two main types of protein kinase. The great majority are serine/threonine kinases, which phosphorylate the hydroxyl groups of serines and threonines in their targets and most of the others are tyrosine kinases, although additional types exist. Protein kinases are also found in bacteria and plants. Up to 30% of all human proteins may be modified by kinase activity, and kinases are known to regulate the majority of cellular pathways, especially those involved in signal transduction.
A mitogen-activated protein kinase is a type of protein kinase that is specific to the amino acids serine and threonine. MAPKs are involved in directing cellular responses to a diverse array of stimuli, such as mitogens, osmotic stress, heat shock and proinflammatory cytokines. They regulate cell functions including proliferation, gene expression, differentiation, mitosis, cell survival, and apoptosis.
A mitogen is a small bioactive protein or peptide that induces a cell to begin cell division, or enhances the rate of division (mitosis). Mitogenesis is the induction (triggering) of mitosis, typically via a mitogen. The mechanism of action of a mitogen is that it triggers signal transduction pathways involving mitogen-activated protein kinase (MAPK), leading to mitosis.
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.
c-Met, also called tyrosine-protein kinase Met or hepatocyte growth factor receptor (HGFR), is a protein that in humans is encoded by the MET gene. The protein possesses tyrosine kinase activity. The primary single chain precursor protein is post-translationally cleaved to produce the alpha and beta subunits, which are disulfide linked to form the mature receptor.
Mitogen Activated Protein (MAP) kinase kinase kinase, MAPKKK is a serine/threonine-specific protein kinase which acts upon MAP kinase kinase. Subsequently, MAP kinase kinase activates MAP kinase. Several types of MAPKKK can exist but are mainly characterized by the MAP kinases they activate. MAPKKKs are stimulated by a large range of stimuli, primarily environmental and intracellular stressors. MAPKKK is responsible for various cell functions such as cell proliferation, cell differentiation, and apoptosis. The duration and intensity of signals determine which pathway ensues. Additionally, the use of protein scaffolds helps to place the MAPKKK in close proximity with its substrate to allow for a reaction. Lastly, because MAPKKK is involved in a series of several pathways, it has been used as a therapeutic target for cancer, amyloidosis, and neurodegenerative diseases. In humans, there are at least 19 genes which encode MAP kinase kinase kinases:
The insulin-like growth factor 1 (IGF-1) receptor is a protein found on the surface of human cells. It is a transmembrane receptor that is activated by a hormone called insulin-like growth factor 1 (IGF-1) and by a related hormone called IGF-2. It belongs to the large class of tyrosine kinase receptors. This receptor mediates the effects of IGF-1, which is a polypeptide protein hormone similar in molecular structure to insulin. IGF-1 plays an important role in growth and continues to have anabolic effects in adults – meaning that it can induce hypertrophy of skeletal muscle and other target tissues. Mice lacking the IGF-1 receptor die late in development, and show a dramatic reduction in body mass. This testifies to the strong growth-promoting effect of this receptor.
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.
Growth factor receptor-bound protein 2 also known as Grb2 is an adaptor protein involved in signal transduction/cell communication. In humans, the GRB2 protein is encoded by the GRB2 gene.
In molecular biology, extracellular signal-regulated kinases (ERKs) or classical MAP kinases are widely expressed protein kinase intracellular signalling molecules that are involved in functions including the regulation of meiosis, mitosis, and postmitotic functions in differentiated cells. Many different stimuli, including growth factors, cytokines, virus infection, ligands for heterotrimeric G protein-coupled receptors, transforming agents, and carcinogens, activate the ERK pathway.
Son of sevenless homolog 1 is a protein that in humans is encoded by the SOS1 gene.
GRB2-associated-binding protein 2 also known as GAB2 is a protein that in humans is encoded by the GAB2 gene.
Protein kinase C delta type is an enzyme that in humans is encoded by the PRKCD gene.
Insulin receptor substrate 1 (IRS-1) is a signaling adapter protein that in humans is encoded by the IRS-1 gene. It is a 131 kDa protein with amino acid sequence of 1242 residues. It contains a single pleckstrin homology (PH) domain at the N-terminus and a PTB domain ca. 40 residues downstream of this, followed by a poorly conserved C-terminus tail. Together with IRS2, IRS3 (pseudogene) and IRS4, it is homologous to the Drosophila protein chico, whose disruption extends the median lifespan of flies up to 48%. Similarly, Irs1 mutant mice experience moderate life extension and delayed age-related pathologies.
Receptor tyrosine-protein kinase erbB-3, also known as HER3, is a membrane bound protein that in humans is encoded by the ERBB3 gene.
Mitogen-activated protein kinase 7 also known as MAP kinase 7 is an enzyme that in humans is encoded by the MAPK7 gene.
Fibroblast growth factor receptor substrate 2 is a protein that in humans is encoded by the FRS2 gene.
The Akt signaling pathway or PI3K-Akt signaling pathway is a signal transduction pathway that promotes survival and growth in response to extracellular signals. Key proteins involved are PI3K and Akt.
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