Cell Signaling & Signal Transduction

1. 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,

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

3. 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

4. g g a a a b b ATP ATP GTP cAMP +PPi cAMP +PPi G-protein Mediated cAMP synthesis GDP GTP When the [hormone] drops… GTP GDP Pi

5. c-AMP: a second messenger

6. Index card assignment g a b ATP cAMP +PPi Watch the animation. Collaborate with your classmates todescribe what’s happening, why it might happen, and how these events are useful. Write your response in your own words on an index card. GTP GDP Pi

7. glycogen glucose-1-phosphate cAMP and the Fight-or-Flight Response; activation of PKA adrenaline Liver cell ATP inactive active cAMP adenylyl cyclase p inactive active cAMP glycogen phosphorylase active p inactive phosphorylase kinase inactive active protein kinase A amplification cascade

8. Prevents the synthesis of cAMP. Prevents the breakdown of cAMP. Inactivates the enzyme protein kinase A. Inhibits the enzyme glycogen phosphorylase Caffeine keeps you awake because it Caffeine inhibits the enzyme phosphodiesterase, which normally breaks down cAMP.

9. Heart muscle contraction mediated by acetylcholine-stimulated G-protein signal transduction pathway

10. IP3 cGMP diacyl glycerol Ca++ protein kinase C Which of the following is not a second messenger resulting from G-protein-mediated signal transduction?

11. G-protein mediated signal transduction is mediated by several 2nd messengers: cAMP protein kinase A Ultimate effects IP3 (inositol triphosphate) OH Adenylate cyclase SER Ca++ Phospholopase C DAG (diacyl glycerol) protein kinase C

12. Protein kinase C effects include: • neurotransmitter release • cell growth & division • cell differentiation • glycogen hydrolysis • fat synthesis • Phospholipase C-mediated effects: • Liver glycogen breakdown (vasopressin) • Pancreatic amylase secretion (acetylcholine) • Platelet aggregation (thrombin)

13. Plant derived phorbol esters are carcinogenic because they mimic DAG, leading to... • constant PKC activity • constant cell growth & division

14. 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.

15. Receptor tyrosine kinase mediated signal transduction • does not involve G-proteins • does involve phosphorylation of proteins • … at tyrosines

16. Receptor Tyrosine Kinase Activation P- X -P P- X -P P- X -P ligands inactive tyr kinase monomer active tyr kinase dimer …cross-phosphorylation of tyrosines ADP ATP Phosphorylated tyrosines on activated signaling proteins  cell response

17. P- X -P P- X -P P- X -P MAP kinase-kinase adaptor protein Ras-activatingprotein MAP kinase translocation to nucleus… MAP (mitogen-activated protein) kinase activation: ligands inactive active active Ras MAP kinase-kinase-kinase inactive tyr kinase monomer active tyr kinase dimer GDP P- GTP cross-phosphorylation of tyrosines ATP ADP P- nucleus

18. MAP kinase Transcription factors Other nuclear proteins DNA binding Changes in protein activity changes in gene activity Cell proliferation, differentiation P | P- P- nucleus

19. One resulting in less Ras gene transcription One resulting in tighter binding of GDP to the Ras protein One resulting in an inability to hydrolyze GTP One resulting in an inbility to phosphorylate MAP kinase-kinase-kinase Many human cancers have mutations affecting the Ras protein. Which of the following kinds of mutations could account for this?

20. 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.

21. PPT presentation ends here

22. Signal transduction themes: 2nd messengers & protein phosphorylation Signal Transduction intracellular second messenger …binds to inactive protein kinase activated protein kinase extracellular signal ATP ADP Pi phosphatase

23. Plant derived phorbol esters are carcinogenic because they mimic DAG, leading to... • constant PKC activity • constant cell growth & division