3/17/15&1&Cell&Signaling&II.&&&G2Protein&coupled&receptors&and&Receptor&Tyrosine&Kinase&pathways&Reading:&ECB3&5422551;5552559;&ECB4&5392548;5512558&Learning&Goals:&1. Know&that&G2Protein&coupled&receptors&are&the&most&abundant&cell&surface&receptors&and&play&important&roles&in&almost&every&cell,&but&are&extremely&important&in&the&nervous&system.&&&2. Be&able&to&describe&in&molecular&detail&how&adrenaline&acQvaQon&of&its&G&protein&coupled&receptor&mediates&both&fast&and&slow&responses.&&&3. Know&that&Receptor&Tyrosine&Kinases&(RTKs)&are&the&major&class&of&enzyme2coupled&receptors;&they&regulate&the&growth,&proliferaQon,&differenQaQon&and&survival&of&cells.&4. Know&that&RTKs&are&acQvated&by&dimerizaQon&that&is&sQmulated&by&binding&to&extracellular&signals&followed&by&cross2phosphorylaQon&of&each&subunit&by&the&other;&RTKs&are&inacQvated&by&protein&tyrosine&phosphatases&or&by&removal&through&endocytosis.&5. Know&that&different&acQvated&RTKs&bind&to&different&sets&of&intracellular&signaling&molecules,&and&be&able&to&describe&three&important&RTK&pathways:&the&MAP&kinase&pathway,&mediated&by&the&monomeric&GTPase&Ras,&and&the&cell&survival&and&cell&growth&pathways&mediated&by&PI23&kinase,&Akt&and&Tor.&&Next&prelim&is&Wednesday&March&25.&&It&will&include&the&two&lectures&on&signaling&this&week.&&AcQve&Learning&secQons&this&week&focus&on&review.&&Special&Office&hours:&!Friday!March!20&&&1:0022:15&Joel&&107&SQmson&Sunday!March!22&&&1:0022:00&Kevin&M&&107&SQmson&Monday!March!23&&&1:0022:00&Jae&&&107&SQmson&&&2:0023:00&Dante&&&107&SQmson&Tuesday!March!24&&&1:00&2&2:00&Kevin&H&&&G04&SQmson&*note&different&locaQon*&&&2:00&2&3:00&Lucy&&&107&SQmson&&&3:00&2&4:00&Jen&&&107&SQmson&&&3/17/15&2&Three&types&of&surface&receptors:&&Ion7channel7coupled!receptors!!G7protein7coupled!receptors!!Enzyme7coupled!receptors!Figure 16-15a Essential Cell Biology (© Garland Science 2010) Found&in&Nerve&and&Muscle&cells&Rapid&(mSec)&responses&Receptors&are&ion&specific&Lead&to&rapid&change&in&membrane&potenQal&If&ion&is&calcium,&can&cause&diverse&cellular&changes.&3/17/15&3&Three&types&of&surface&receptors:&&Ion7channel7coupled!receptors!!G7protein!coupled!receptors!!Enzyme7coupled!receptors!√#ac?vated!α!subunit!GTP!hydrolysis!Trimeric&G2Protein&ON&OFF&type of GTP-binding protein for intracellular signaling pathways - relay messages from G-protein-coupled receptorsalso called G proteinsGTP binding activates G protein GTP hydrolysis deactivates G protein3/17/15&4&Figure 16-15b Essential Cell Biology (© Garland Science 2010) (three&subunit&or&trimeric!G7protein)&Receptors&are&always!seven!pass!transmembrane&proteins.&G2Proteins&frequently&signal&via&the&second&messengers&cAMP&and&Ca2+!A) - receptor and G protein are both inactive B) - extracellular signal molecule binds to the receptor -> changes the conformation of the receptor and the bound G protein - alpha subunit is altered. G protein is allowed to exchange GDP for GTP - exchange activates alpha subunit and By complex. - receptor stays active as long as the external signal molecule is bound to it -> so it can catalyze the activation of many molecules of G protein3/17/15&5&ATP&cAMP!cAMP!phosphodiesterase!AMP&(Adenylyl!cyclase)!(modified)&- enzymes activated by G proteins increase the concentrations of small intracellular signaling molecules - signal is amplified at this step because each activated enzyme generates many molecules of these 2nd messengers - signal is relayed onward by the 2nd messenger molecules. - 2nd messenger molecules bind to specific signaling proteins in the cell and influence their activitycyclic AMP (cAMP) is synthesized by adenylyl cyclase and degraded by cyclic AMP phosphodiesterase 1) ATP has 2 phosphate groups removed 2) adenyly cyclase joins to sugar part of AMP molecule 3) dehydration reaction (addition of H20) breaks new bond forming AMP3/17/15&6&The&producQon&of&cAMP&is&rapid&and&dramaQc&–&more&than&20&fold&in&20&seconds.&G2protein&signaling&through&cAMP&in&muscle&cells&triggers&increased&producQon&of&glucose&from&glycogen.&&(We&discussed&this&same&pathway&on&Monday.)&cAMP concentration rises rapidly in response to an extracellular signal adrenaline stimulates glycogen breakdown in skeletal muscle cells1) hormone activates a GPCR 2) GPCR turns on a G protein (Gs) that activates adenylyl cyclase to boost the production of cAMP 3) PKA is activated by the increase in cAMP 4) PKA phosphorylates and activates an enzyme that breaks down glycogen *reaction happens quickly because doesn't involve changes in gene transcription or new protein synthesis3/17/15&7&The&same&signaling&system&&can&influence&gene&expression.&&Note&that&the&response&will&depend&upon&which&transcripQonal&regulators&are&present&in&the&cell.&You&don’t&need&to&learn&this&pathway,&but&it’s&cool!&Other&G2protein&coupled&receptors&acQvate&an&enzyme&that&leads&to&the&producQon&of&Ca2+&increase in cAMP can activate gene transcription 1) increase in cAMP activates PKA 2) PKA moves into nucleus and phosphorylates specific transcription regulators 3) proteins are phosphorylated. then stimulate transcription of a whole set of target genes.3/17/15&8&Phosphorylated&receptors&taken&into&the&cell&by&receptor&mediated&endocytosis&and&sent&to&the&lysosome&or&recycled&to&the&plasma&membrane.&Adapted&from&Figure&16217in&ECB3&How&are&GPRC&receptors&inacQvated?&phosphorylation followed by receptor mediated endocytosis3/17/15&9&Three&types&of&surface&receptors:&&Ion7channel7coupled!receptors!!G7protein!coupled!receptors!!Enzyme7coupled!receptors!√#√#Figure 16-15c Essential Cell Biology (© Garland Science 2010)3/17/15&10&Major&families&of&enzyme2coupled&receptors&Ligand/receptor& Enzyme&or&effector&Cytokines/cytokine&receptors& Tyrosine&kinase&TGF2β/TGF2β&receptors& Serine&threonine&kinase&Wnt/frizzled& Disheveled&(inhibits&S/T&kinase)&Hedgehog/patched& && Smoothened&(inhibits&S/T&kinase)&TNF/TNF&receptors# serine&threonine&kinase&Delta/Notch& protease&(Mul?ple)/Receptor!Tyrosine!Kinases*!Tyrosine!kinase!*Note:&&There&are&also&non2receptor&tyrosine&kinases,&like&src.&&&(Don’t&memorize&this&table)&Figure 16-30 Essential Cell Biology (© Garland Science 2010)