The phosphatidylinositol 3' –kinase (PI3K)-Akt signaling pathway is an intracellular signaling pathway important in regulating the cell cycle and is activated by many types of cellular stimuli or toxic insults.
It regulates fundamental cellular functions such as transcription, translation, proliferation, growth, and survival in response to extracellular signals. This is mediated through serine and/or threonine phosphorylation of a range of downstream substrates.
As shown in following picture, activation of growth factor receptor protein tyrosine kinases including epidermal growth factor receptor (EGFR) by external growth factors results in auto-phosphorylation on tyrosine residues and subsequent events to activate these intracellular pathways.
PI3K is recruited to the membrane by directly binding to phosphotyrosine consensus residues of growth factor receptors or adaptors through one or both SH2 domains in the adaptor subunit. This leads to allosteric activation of the catalytic subunit. Activation results in production of the second messenger phosphatidylinositol-3, 4, 5-trisphosphate (PIP3).
The lipid product of PI3K, PIP3, recruits a subset of signaling proteins with pleckstrin homology (PH) domains to the membrane, including PDK1 and Akt. PTEN, is a PI-3, 4, 5-P3 phosphatase, which negatively regulates the PI3K/Akt pathway.
Once activated, Akt mediates the activation and inhibition of several targets, resulting in cellular survival, growth and proliferation through various mechanisms. In the mechanism of PI3K-Akt signaling pathway, the key molecules involved in this signaling pathway are receptor tyrosine kinase (RTKs), phosphatidylinositol 3-kinase (PI3K), phosphatidylinositol-4,5-bisphosphate (PIP2), phosphatidylinositol-3,4,5-bisphosphate (PIP3) and AKT/protein kinase B.
Most genetic alterations associated with tumor phenotype are representative of a finite succession of physiologic disturbances, which, collectively, render the cell to become malignant. Alterations of the PI3K-Akt signaling pathway have been reported in numerous human cancers. The PI3K-Akt signaling pathway plays an important role in the characteristic process of cancer. For example, Akt overexpression or activation may lead to an increased response to ambient levels of growth factors. Sustained activation of Akt makes tumor cells insensitive to anti-proliferative signals by inducing nuclear entry of Mdm2, which leads to inhibition of p53 regulated processes and by inducing cytoplasmic localization of p21Cip/Waf1 and p27Kip, which promotes proliferation. Akt activation also suppresses apoptosis of cancer cells by inactivating pro-apoptotic factors Bad and pro-caspase-9, but by activating IKK that provokes the transcription of NF-κB regulated antiapoptotic genes. Besides, the PI3K-Akt pathway also promotes tumor angiogenesis through eNOS activation and contributes to invasiveness by inhibiting anoikis and stimulating MMP secretion.
There are numerous aberrant mutations of the PI3K-Akt pathway in human cancers, including loss of the lipid phosphatases PTEN and INPP4B, as well as mutation and amplification of the genes encoding the PI3K catalytic subunits p110α (PIK3CA) and p110β (PIK3CB), and so on. In recent clinic cancer treatment, several drugs targeting the PI3K-Akt pathway have been developed and are currently in clinical trials in different phases of clinical development, such as PI3K Inhibitors, Isoform-Specific PI3K Inhibitors, Dual PI3K/mTOR Inhibitors. However, these drugs are just observed early signals of clinical activity. A better understanding of this essential crossroad between PI3K-Akt signaling and cancer is conducive to fully exploit the potential benefits of these new drugs.
Under normal conditions, insulin is immediately secreted after a meal. The released insulin binds to and activates IRS-1/2 (insulin receptor substrate-1/2), initiating the PI3K-Akt signaling pathway. Insulin-mediated Akt pathway accelerates glucose utilization, reduces gluconeogenesis of liver and muscle, increases body lipid deposition, thereby reducing free fatty acid (FFA) circulation in adipose tissue, increases pancreatic insulin secretion, and regulates lipid and glucose metabolism balance, reduce brain appetite. However, in the case of chronic energy excessive conditions, such as obesity, lipid accumulation is saturated, resulting in increased lipolysis of adipose tissue, leading to excessive FFAs. Lipid ectopic accumulation of skeletal muscle leads to reduced glucose transport and glycogen synthesis. Excess FAAs also disrupts β-cell function and insulin secretion. In the liver, excess FAAs suppress extrahepatic insulin signal transduction and ectopic accumulation of lipids, leading to an increase in HGP (hepatic glucose production) and DNL (de novo lipogenesis). In the brain, excessive FFAs cause glucose and lipid metabolism disorders. All these eventually impairs the PI3K-Akt signal, inducing insulin resistance. Insulin resistance further exacerbates the PI3K-AKT signal, forming a vicious circle that leads to obesity and Type II diabetes. As the PI3K-Akt pathway is closely related to metabolism, regulation of PI3K-Akt signaling pathway and its downstream molecules is a potential therapeutic target for the treatment of obesity and type 2 diabetes.
|LPAR1||LPAR1 Antibody||LPAR1 Protein||LPAR1 cDNA||LPAR1 ELISA Kit|
|LPAR2||LPAR2 Antibody||LPAR2 Protein||LPAR2 cDNA||LPAR2 ELISA Kit|
|LPAR3||LPAR3 Antibody||LPAR3 Protein||LPAR3 cDNA||LPAR3 ELISA Kit|
|LPAR4||LPAR4 Antibody||LPAR4 Protein||LPAR4 cDNA||LPAR4 ELISA Kit|
|LPAR5||LPAR5 Antibody||LPAR5 Protein||LPAR5 cDNA||LPAR5 ELISA Kit|
|LPAR6||LPAR6 Antibody||LPAR6 Protein||LPAR6 cDNA||LPAR6 ELISA Kit|
|MAP2K1||MAP2K1 Antibody||MAP2K1 Protein||MAP2K1 cDNA||MAP2K1 ELISA Kit|
|MAP2K2||MAP2K2 Antibody||MAP2K2 Protein||MAP2K2 cDNA||MAP2K2 ELISA Kit|
|MAPK1||MAPK1 Antibody||MAPK1 Protein||MAPK1 cDNA||MAPK1 ELISA Kit|
|MAPK3||MAPK3 Antibody||MAPK3 Protein||MAPK3 cDNA||MAPK3 ELISA Kit|
|MCL1||MCL1 Antibody||MCL1 Protein||MCL1 cDNA||MCL1 ELISA Kit|
|MDM2||MDM2 Antibody||MDM2 Protein||MDM2 cDNA||MDM2 ELISA Kit|
|MET||MET Antibody||MET Protein||MET cDNA||MET ELISA Kit|
|MLST8||MLST8 Antibody||MLST8 Protein||MLST8 cDNA||MLST8 ELISA Kit|
|MTCP1||MTCP1 Antibody||MTCP1 Protein||MTCP1 cDNA||MTCP1 ELISA Kit|
|MTOR||MTOR Antibody||MTOR Protein||MTOR cDNA||MTOR ELISA Kit|
|MYB||MYB Antibody||MYB Protein||MYB cDNA||MYB ELISA Kit|
|MYC||MYC Antibody||MYC Protein||MYC cDNA||MYC ELISA Kit|
|NFKB1||NFKB1 Antibody||NFKB1 Protein||NFKB1 cDNA||NFKB1 ELISA Kit|
|NGF||NGF Antibody||NGF Protein||NGF cDNA||NGF ELISA Kit|