Bio202 Lecture 10: Cell Signaling Part 2 PDF

Lecture 10: Cell Signaling Part 2 https://www.jneurosci.org/content/34/47.cover-expansion  Today’s agenda - Quick refresher on molecular switches - Cell surface receptors - Cross-talk and integration of signaling pathways - Untangling a signaling pathway - Fun with cell...

Lecture 10: Cell Signaling Part 2 https://www.jneurosci.org/content/34/47.cover-expansion  Today’s agenda - Quick refresher on molecular switches - Cell surface receptors - Cross-talk and integration of signaling pathways - Untangling a signaling pathway - Fun with cell signaling  Many intracellular signaling proteins act as molecular switches phosphorylation can turn some proteins monomeric GTPases are on when bound Figure 16-11 on, as shown here, and others off to GTP and off when bound to GDP  Cell surface receptors fall into one of three main classes Figure 16-13  Figure 16-13 - Open in response to binding an extracellular signaling molecule - Ions of the correct size and charge then pass through the channel - The ions move with the concentration gradient (move from high to low concentration)  Cell surface receptors fall into one of three main classes Figure 16-13  Figure 16-13 - Activate membrane-bound, trimeric GTP-binding proteins (G proteins) - trimeric means a G protein is composed of three proteins - Activated G proteins then go on to activate a downstream component in the signaling cascade G-protein-coupled-receptors (GPCRs) - The largest family of cell surface receptors - >700 in humans - Bind to a wide variety of extracellular signaling molecules, including hormones, neurotransmitters, and local mediators - Involved in an enormous variety of cellular processes, which make them an attractive target for drug development - >1/3 of drugs used today work on GPCRs - All have a similar structure – pass through the membrane 7 times (i.e. have 7 transmembrane domains) Figure 16-14  Activation of a G protein by an activated GPCR - G proteins are trimeric; they have alpha, beta, and gamma protein subunits - In an unstimulated state, the receptor and G protein are both inactive - Binding of an extracellular signal to the receptor causes a conformational change of the receptor, which in turn alters the conformation of the bound G protein - The conformational change of the G protein allows it to exchange its GDP for GTP - When bound to GTP, the beta and gamma subunits dissociate from the alpha subunit - The alpha subunit and beta-gamma complex are now active and activate downstream Figure 16-15 components in the signaling pathway Inactivation of a G protein - For G-proteins, the α subunit has an intrinsic GTPase activity, and it eventually hydrolyzes its bound GTP to GDP - GTP hydrolysis usually occurs within seconds of activation - Following GTP hydrolysis, the alpha subunit reassociates with the beta-gamma complex to reform the inactive G-protein - No GAP is needed! Figure 16-16  From Inner Life of a Cell: a chemokine activating a GPCR A chemokine is an extracellular signaling molecule from a family of signaling molecules known as cytokines; chemokines affect cell migration when they activate a GPCR.  G protein versus monomeric GTPase inactivation Figure 16-16 Figure 16-12  Cell surface receptors fall into one of three main classes Figure 16-13 - Either act as enzymes or associate with enzymes inside the cell - When stimulated, the enzymes can activate a wide variety of intracellular signaling pathways  Receptor tyrosine kinases (RTKs) – the largest class of enzyme coupled receptors Figure 16-29 - The cytosolic domain of RTKs functions as a tyrosine kinase - Binding of a signaling molecule causes two RTKs to associate into a dimer - Dimerization brings the kinase domain of one receptor in contact with the other - The kinase domain of one receptor phosphorylates the kinase domain of the other - Each phosphorylated tyrosine serves as a docking site for a different intracellular signaling protein, which helps to relay the signal  Activation of the monomeric GTPase Ras by RTKs Figure 16-31  Intracellular signaling cascades use a combination of mechanisms to transmit the signal Figure 16-32  Receptors can activate multiple pathways and sometimes use common components to transmit their signals Figure 16-36  Intracellular signaling proteins serve to integrate incoming signals – a way to fine-tune a cells response In this case, the target protein needs to be phosphorylated by kinase 1 and kinase 2, which are activated by different upstream signaling pathways Figure 16-44  Untangling cell signaling pathways A signaling pathway involves 3 proteins: Ras (a monomeric GTPase), Protein X, and Protein Y Based on the experiments described below… Is Protein X upstream or downstream of Ras in the signaling pathway? Is Protein Y upstream or downstream of Ras in the signaling pathway? How can you make an overactive (always active) form of Ras? Ras Ras is a is a small, small, monomeric monomeric GTPase GTPase Figure 16-38  Untangling cell signaling pathways A signaling pathway involves 3 proteins: Ras (a monomeric GTPase), Protein X, and Protein Y Based on the experiments described below… Is Protein X upstream or downstream of Ras in the signaling pathway? Is Protein Y upstream or downstream of Ras in the signaling pathway? How can you make an overactive (always active) form of Ras? Ras is a small, monomeric GTPase Figure 16-38 Figure 16-38  Untangling cell signaling pathways A signaling pathway involves 3 proteins: Ras (a monomeric GTPase), Protein X, and Protein Y Based on the experiments described below… Is Protein X upstream or downstream of Ras in the signaling pathway? Is Protein Y upstream or downstream of Ras in the signaling pathway? How can you make an overactive (always active) form of Ras? How? Figure 16-38 Prof. Carole LaBonne Prof. Keara Lane Molecular Biosciences Molecular Biosciences Signaling pathways in Signaling pathways in development and host-pathogen disease interactions Prof. Reza Vafabakhsh Prof. Christian Petersen Molecular Biosciences Molecular Biosciences G protein coupled Signaling pathways in receptors animal regeneration  Fun with cell signaling https://www.jneurosci.org/content/34/47.cover-expansion Planaria have the ability to regenerate Planaria have the ability to regenerate Neoblasts: planarian stem cells that are critical for regeneration https://dev.biologists.org/content/140/5/951 Planaria have the ability to regenerate How do planaria know what cells to regenerate? Cell signaling is critical for proper regeneration wnt and hedgehog are signaling molecules éwnt êwnt éhedgehog  Next class: Exam 2 review session Next lecture: The Cytoskeleton brought to you by Prof. Wignall 31 www.microscopyu.com; Khodjakov – Wadsworth; Cowan – Harvard