Tyrosine kinases and Insulin receptor (BT-710): Tyrosine kinases and Insulin receptor (BT-710) SATYENDER KUMAR PH.D SCHOLAR NIPER AHMADABAD, GUJRAT INTRODUCTION: INTRODUCTION SIGNAL TRANSDUCTION PATHWAYS Allow the cell to sense and respond to signals in the environment. Signal Receptor Transducer Effectors Response Upstream Downstream PowerPoint Presentation: Figure 1: Schematic diagram of generalized signal transduction pathways INTRODUCTION: INTRODUCTION Signals: start the whole thing. They’re what the target cell senses. Receptors: sense the signal and are activated. Sensing the signal causes a change in the structure of the receptor. This structural change activates the pathway. Cytosolic receptors are soluble, cytoplasmic proteins (signal must get inside) and Transmembrane receptors span a membrane (i.e., signal outside, response inside). Transducers: receive the signal and then pass it on in a different form. They can amplify the signal or integrate signals from multiple pathways. Most components of signal transduction pathways can be considered transducers. Second messengers: small molecules that are released in the cell in response to a signal. They can activate many other downstream components. Amplifiers: increase the strength of the signal. They turn one molecule of original signal into many, many molecules of second messengers or secondary signals. Integrators: allow multiple signals to converge on a single response. Effectors: the final step of the signaling pathway. Their activation results in the effect. Sometimes signals can activate multiple pathways and have multiple effects. Inhibitors: turn off signaling pathways. Activating an inhibitor has the same effect as inactivating the signaling event. INTRODUCTION: INTRODUCTION Types of receptors: 1. Soluble receptors 2. Transmembrane receptors a. Enzyme coupled receptors Tyrosine kinase Phospholipase-C b. G-Protein coupled receptors c-AMP or Ca 2+ ions c. Ion-channel coupled receptors SIGNAL TRANSDUCTION PATHWAYS: SIGNAL TRANSDUCTION PATHWAYS Figure 2: Soluble intracellular receptor Hormone SIGNAL TRANSDUCTION PATHWAYS: SIGNAL TRANSDUCTION PATHWAYS Figure 3: Transmembrane receptor Protein tyrosine residue Activated Phosphorylate Protein tyrosine SIGNAL TRANSDUCTION PATHWAYS: SIGNAL TRANSDUCTION PATHWAYS Figure 4: Tyrosine kinae coupled transmembrane receptor SIGNAL TRANSDUCTION PATHWAYS: SIGNAL TRANSDUCTION PATHWAYS Figure 5: Ion channel coupled transmembrane receptor SIGNAL TRANSDUCTION PATHWAYS: SIGNAL TRANSDUCTION PATHWAYS Figure 6: Phospolipase-C enzyme coupled receptor SIGNAL TRANSDUCTION PATHWAYS: SIGNAL TRANSDUCTION PATHWAYS Figure 7: Ion channel coupled receptor SIGNAL TRANSDUCTION PATHWAYS: SIGNAL TRANSDUCTION PATHWAYS Figure 8: The phosphorylation state of a protein target is determined by the relative activities of the kinase that activates it and the phosphatase that inactivates it. When the signaling event is over, the phosphatase returns the protein target to the inactive state. PowerPoint Presentation: Examples: Tyrosine Kinases (TK or RTK): Tyrosine Kinases (TK or RTK) Tyrosine kinase is a receptor protein that exists as β transmembrane chain attached through a disulfide bond to an α chain on the outside of the membrane. Each αβ complex is referred to as a monomeric subunit. Binding of insulin to the RP promotes dimerization of the αβ subunits and TK becomes active. One insulin molecule is bound between the two subunits. Insulin Structure: Insulin Structure β - subunit α - subunit Receptor Tyrosine Kinase: Receptor Tyrosine Kinase Insulin receptor: Insulin receptor Figure 9: Transmembrane insulin receptor signaling cascade Tyrosine Kinases: Tyrosine Kinases Active TK subunits phosphorylate each other at Tyr in both β chains on the cytosolic side of the αβαβ dimer. This process uses ATP and is known as autophosphorylation. Autophosphorylation induces a conformation change, activating the kinase form of TK. TK can now phosphorylate certain cytosolic proteins at tyrosine. So, this receptor protein is also a kinase (an effector protein). PowerPoint Presentation: Autophosphorylation Figure 10: Activation of the insulin-receptor Tyr kinase by autophosphorylation. Autophosphorylation TK Phosphorylation: TK Phosphorylation Tyrosine Phosphorylated Tyrosine Phosphate group Tyrosine Kinases: Tyrosine Kinases TK acts on a group of small proteins called insulin receptor substrates (IRS) that are phosphorylated at Tyr in 4 Tyr-X-X-Met sequences. IRS then coordinates association among TK, PIP 2 and phosphoinositide-3 kinase ( PI-3K). PI-3K has a SH2 domain used to bind Tyr-P. PI 3-kinase uses PIP 2 as substrate and phosphorylates the 3 position of inositol. PIP 2 + ATP ----> PI-3,4,5-trisP (PIP 3 ) + ADP PIP3 : PIP 3 Tyrosine Kinase System: Tyrosine Kinase System Figure 11: Regulation of gene expression by insulin: Figure 11: Regulation of gene expression by insulin Tyrosine Kinases: Tyrosine Kinases PIP 3 is a membrane bound second messenger that activates certain protein kinases, such as 3-phosphoinositide-dependent protein kinase 1 (PDK1) which is a membrane bound Ser/ Thr kinase. PDK-1 phosphorylates other mobile kinases in the cytosol such as Akt (protein kinase B) which is also a Ser/ Thr kinase. Tyrosine Kinases: Tyrosine Kinases Insulin signaling is terminated by dissociation of insulin from the receptor. The activation process that has been initiated is deactivated via dephosphorylation of the various sites to which phosphate has been attached. Several types of phosphatases are important here: Protein tyrosine phosphatase for Tyr-P , Lipid phosphatases for PIP 3 and Protein serine phosphatases for Ser-P / Thr -P. Figure 12: Downstream activation of glycogen synthase by insulin. : Figure 12: Downstream activation of glycogen synthase by insulin. Figure 13: The JAK-STAT transduction mechanism for the erythropoietin receptor (example of Tyrosine Kinase Receptor JAK) : Figure 13: The JAK-STAT transduction mechanism for the erythropoietin receptor (example of Tyrosine Kinase Receptor JAK) JAK : Janus kinase STAT : Signal transducers and activators of transcription Example of mechanism of erythropoietin receptor by tyrosine kinase receptor JAK PowerPoint Presentation: Any Questions????????