SC430 Molecular Cell Biology

1. SC430 Molecular Cell Biology • Welcome to Unit 7 Seminar with Dr Hall-Pogar • Tonight we will discuss • Diseases that result from errors in cell signaling pathways and available treatments • I will be available at AIM:KaplanHallPogar before and throughout the seminar if you have any questions or issues. • We will begin promptly at 8:00pmEST

2. Unit Review • DB • Quiz • Project • Due this Unit 7 • Part I: Protein Synthesis • Part II: Protein Mutations

3. Cell to Cell Communication • Juxtacrine signaling - with each other via direct contact • Paracrine signaling - over short distances • Endocrine signaling - over large distances • Some cell-to-cell communication requires direct cell-cell contactcellsform gap junctions

4. Cell signaling: responding to the outside world • Cells interact with their environment by interpreting extracellular signals via proteins that span their plasma membrane called receptors • Receptors are comprised of extracellular and intracellular domains • The extracellular domain relays information about the outside world to the intracellular domain • The intracellular domain then interacts with other intracellular signalingproteins • These intracellular signaling proteins further relay the message to one or more effector proteins • Effector proteins mediate the appropriate response

5. Receiving the Signal: G-protein Coupled Receptors (GPCRs) • GPCRs are an important and ubiquitous class of eukaryotic receptors (>700 in humans) • The intracellular domain is coupled to a heterotrimeric G-protein • When the G subunit is bound to GDP it is “OFF”; when it is bound to GTP it is “ON” • When the extracellular domain binds to the signal molecule, it causes a conformational change relayed through the transmembrane spans to the intracellular domain • The conformational change relayed to the intracellular domain causes the G subunit to release GDP and bind to GTP thereby activating both the G and G/G subunits

6. What are G-proteins? • G proteins bind GTP: guanosine triphosphate. Control and amplify intracellular signaling pathways Exist in two states 1) bound GTP: active 2) bound GDP: inactive (hormone, GF, drug) Examples of GTPase proteins Ras, Cdc-42 Fig. 15.1

7. GTPases and disease. • Damage to these small GTPase switches can have catastrophic consequences for the cell and the organism. • Several small GTPases of the Rac/Rho subfamily are direct targets for clostridial cytotoxins. • Ras proteins are mutated to a constitutively-active (GTP-bound) form in approximately 20% of human cancers.

8. Insulin Signal Transduction Cascades Insulin Promotes Cell growth, Glucose uptake and storage Insulin Receptors (IR) bind 2 insulin peptide with 2 α chains β chains (auto-)phosphorylate each other P- β subunits now active tyrosine kinases Active RTK initiates a signal transduction cascade RTK phosphorylates Insulin Receptor Substrate-1 (IRS-1) Adaptor proteins Grb2 and Sos bind to P-Tyr-IRS-1 via SH2 domain Sos activates Ras GTPase Ras.GTP activatesProtein Kinase Cascade Ras activates Raf-1 kinase (MAPKKK) Raf-1 kinase activates MEK kinase (MAPKK) MEK kinase activates ERK kinase (MAPKinase) ERK kinase activates Elk1 transcriptional activator

9. Disease caused by • Nature of these defects and how they are induced varies enormously • Examples include pathogenic organisms and viruses (Cholera, peptic ulcers, Chlamydial diseases) • Mutations • Environmental causes • Remodeling of signal pathways • Redundancy built into cell signaling mechanisms offers opportunities for discovering new ways of correcting many disease states

11. Treatment Options • Small molecule inhibitors • Antibodies or receptors • Replacement signal molecules • microRNA