UW-M Cell Biology (Bio Sci 315) Cell Signaling & Signal Transduction Steroid hormones (also thyroid hormone) enter cells to regulate gene expression. Signal molecules too big or polar to enter a target cell transmit information by signal transduction,

UW-M Cell Biology (Bio Sci 315) 1. large or very polar extracellular ligand (e.g., hormone) 1. large or very polar extracellular ligand (e.g., hormone) changes in enzyme activity Signal Transduction Themes: intracellular 2nd messengers Protein phosphorylation 3. intracellular 2nd messengers 4. protein phosphorylation changes in cytoskeletal organization changes in ion permeabilty activation of replication regulation of transcription 2. cell surface receptor 2. cell surface receptor Membrane depolarization

UW-M Cell Biology (Bio Sci 315) Overview of the 3 Main Signal Transduction Pathways: e.g., neurotransmission e.g., cAMP mediated flight or fight response (glycogen breakdown, muscle contraction) e.g., regulation of many genes

UW-M Cell Biology (Bio Sci 315) G-protein Mediated cAMP synthesis    GTP GDP  GTP ATP cAMP +PPi    GTP ATP cAMP +PPi GDP Pi When the [hormone] drops…

UW-M Cell Biology (Bio Sci 315) c-AMP: a second messenger

UW-M Cell Biology (Bio Sci 315) ATP cAMP +PPi    GTP GDP Pi Index card assignment Watch the animation. Collaborate with your classmates to describe what’s happening, why it might happen, and how these events are useful. Write your response in your own words on an index card.

UW-M Cell Biology (Bio Sci 315) cAMP and the Fight-or-Flight Response; activation of PKA cAMP adrenaline inactive adenylyl cyclase inactiveactive protein kinase A phosphorylase kinase p p glycogen phosphorylase glycogen glucose-1-phosphate Liver cell amplification cascade cAMP active ATP inactive active

UW-M Cell Biology (Bio Sci 315) Caffeine keeps you awake because it 1.Prevents the synthesis of cAMP. 2.Prevents the breakdown of cAMP. 3.Inactivates the enzyme protein kinase A. 4.Inhibits the enzyme glycogen phosphorylase Caffeine inhibits the enzyme phosphodiesterase, which normally breaks down cAMP.

UW-M Cell Biology (Bio Sci 315) Heart muscle contraction mediated by acetylcholine- stimulated G-protein signal transduction pathway

UW-M Cell Biology (Bio Sci 315) Which of the following is not a second messenger resulting from G-protein- mediated signal transduction? 1.IP 3 2.cGMP 3.diacyl glycerol 4.Ca++ 5.protein kinase C

UW-M Cell Biology (Bio Sci 315) SER IP 3 (inositol triphosphate) Ca ++ G-protein mediated signal transduction is mediated by several 2 nd messengers: DAG (diacyl glycerol) OH protein kinase C Ultimate effects cAMP protein kinase A Adenylate cyclase Phospholopase C

UW-M Cell Biology (Bio Sci 315) Phospholipase C-mediated effects: Liver glycogen breakdown (vasopressin) Pancreatic amylase secretion (acetylcholine) Platelet aggregation (thrombin) Protein kinase C effects include: neurotransmitter release cell growth & division cell differentiation glycogen hydrolysis fat synthesis

UW-M Cell Biology (Bio Sci 315) Plant derived phorbol esters are carcinogenic because they mimic DAG, leading to... constant PKC activity constant cell growth & division

UW-M Cell Biology (Bio Sci 315) PK-A and PK-C (activated by G- protein mediated signal transduction) are serine-threonine kinases because they place phosphates on these amino acids in target proteins.

UW-M Cell Biology (Bio Sci 315) Receptor tyrosine kinase mediated signal transduction does not involve G-proteins does involve phosphorylation of proteins … at tyrosines

UW-M Cell Biology (Bio Sci 315) ligands inactive tyr kinase monomer …cross-phosphorylation of tyrosines Receptor Tyrosine Kinase Activation ATPADP Phosphorylated tyrosines on activated signaling proteins  cell response P- -P active tyr kinase dimer X X X

UW-M Cell Biology (Bio Sci 315) ligands inactive tyr kinase monomer cross- phosphorylation of tyrosines MAP (mitogen-activated protein) kinase activation: ATPADP P- -P active tyr kinase dimer X X X adaptor protein Ras-activatingprotein GDP GTP Ras inactive active MAP kinase-kinase-kinase active MAP kinase-kinase MAP kinase nucleus P- translocation to nucleus…

UW-M Cell Biology (Bio Sci 315) P|P| MAP kinase nucleus Transcription factors Other nuclear proteins P- DNA binding Changes in protein activity changes in gene activity Cell proliferation, differentiation

UW-M Cell Biology (Bio Sci 315) Many human cancers have mutations affecting the Ras protein. Which of the following kinds of mutations could account for this? 1.One resulting in less Ras gene transcription 2.One resulting in tighter binding of GDP to the Ras protein 3.One resulting in an inability to hydrolyze GTP 4.One resulting in an inbility to phosphorylate MAP kinase-kinase- kinase

UW-M Cell Biology (Bio Sci 315) Some final thoughts on signal transduction Signal Transduction is mediated by other kinds of receptor-enzymes Signals include protein hormones, growth factors and cytokines (the latter are signals between nearby cells). Signalling pathways can be direct, like those discussed here, or… They can be complex, requiring the cooperation of two or more signal molecules and the integration of intracellular signalling pathways.

UW-M Cell Biology (Bio Sci 315) PPT presentation ends here

UW-M Cell Biology (Bio Sci 315) Signal transduction themes: 2nd messengers & protein phosphorylation extracellular signal intracellular second messenger Signal Transduction …binds to inactive protein kinase activated protein kinase phosphatase ATP Pi ADP

UW-M Cell Biology (Bio Sci 315) Plant derived phorbol esters are carcinogenic because they mimic DAG, leading to... constant PKC activity constant cell growth & division