Signaling Chapter 12, pp. 433-460, 471-472 February 20, 2014

1. BC368 Biochemistry of the Cell II Signaling Chapter 12, pp. 433-460, 471-472 February 20, 2014

2. Signal transduction • Binding of acetylcholine to its receptor opens the ion channel. • Signal = acetylcholine • Response= ions flow

3. Signal transduction Feedback Regulation Amplification

4. Types of signals

5. Fig. 12-1 Properties of signal transduction

6. Fig. 12-1 Properties of signal transduction

7. Fig. 12-1 Properties of signal transduction

8. Fig. 12-1 Properties of signal transduction

9. Fig. 12-1 Properties of signal transduction • In other words, signaling proteins can interact with more than one target, forming complexes with different properties.

10. Types of chemical signals • Cells communicate with each other by sending out signaling molecules. • In order to respond to the signal, target cell must have a receptor. • Mechanism of signal transduction depends on the chemistry of the transmitter.

11. Interfering with chemical signals • Some molecules interfere with the normal signaling pathway.

12. Interfering with chemical signals • Some molecules interfere with the normal signaling pathway. • Agonists bind to the receptor and mimic the effects of the normal signal.

13. Interfering with chemical signals • Some molecules interfere with the normal signaling pathway. • Agonists bind to the receptor and mimic the effects of the normal signal. • Antagonists act as competitive inhibitors of the normal signal.

14. Types of signal transducers ✓

15. Nuclear receptors • Nonpolar signal molecules can pass through the plasma membrane. Steroid hormones Thyroid hormones

16. Nuclear receptors • Nonpolar signal molecules can pass through the plasma membrane. • Receptor can be in cytosol or nucleus. • Hormone-receptor complex acts in the nucleus to affect gene expression.

17. Nuclear receptors

18. Problems with steroid signaling • Females who produce excess testosterone can have hyperandrogenism. Caster Semenya 2009 World 800-Meter Champion • Individuals who have a defective testosterone receptor have androgen insensitivity. Jazz singer Eden Atwood X,Y Genotype

19. Anabolic Steroids • Anabolic steroids are testosterone agonists used to build skeletal muscle and stimulate bone growth. • Their use in sports was pioneered by East Germany, which had a systematic governmental doping program from 1965 to 1990.

20. Anabolic Steroids • At the first world swimming championships, in 1973, East German women won 10 of the 14 gold medals available, setting eight world records. • Three years later at the Montreal Summer Olympics, the East German women won 11 of 13 events. llona Slupianek Shot Put World Record Holder 1980 –1984

21. Mifepristone (RU486) • Progesterone signaling supports gestation.

22. Mifepristone (RU486) • Progesterone signaling supports gestation. • RU486 (“the abortion pill”) is a progesterone antagonist.

23. Thyroid Hormones • The thyroid normally produces T3 and T4, hormones that help in regulation of metabolism. • Heavy athletic training may suppress the body's production of thyroid hormones.

24. Thyroid Hormones • In 1996, endocrinologist Dr. Jeffrey Brown diagnosed sprinter Carl Lewis with exercise-induced hypothyroidism and prescribed levothyroxine (T4). • Brown’s patients have won 15 Olympic gold medals.

25. Thyroid Hormones • In 1996, endocrinologist Dr. Jeffrey Brown diagnosed sprinter Carl Lewis with exercise-induced hypothyroidism and prescribed levothyroxine (T4). • Brown’s patients have won 15 Olympic gold medals.

26. Types of signal transducers ✓ ✓

27. G-protein coupled receptors

28. GS-protein pathway: β-adrenergic receptor

29. cAMP: second messenger

30. G-protein activation • A GTP Switch protein is active when GTP is bound; inactive when GDP is bound.

31. G-protein activation • When α subunit binds GTP, it separates from β and γ. • Activated α subunit finds AC and turns it on. • Intrinsic GTPase activity turns α subunit off- it finds β and γ.

32. Activation of AC • Activated AC makes cAMP. • One target of cAMP is protein kinase A (PKA).

33. Activation of Protein Kinase A • PKA is active only when 4 cAMP are bound, freeing the two catalytic subunits. • Active PKA has many effects, depending on cell type.

34. Activation of Protein Kinase A

36. Inhibitory G proteins

37. Case Study Peter T., a teacher aged 42, had just returned from Calcutta. Within 24 h of his arrival, he had suddenly developed diarrhea. It was not associated with pain, and as it was watery and voluminous, P.T. took plenty of tea to make up the body fluid. As his condition worsened, with fluid losses up to 1 L/h and with vomiting and muscle cramps, he called his doctor. On examination, P.T. was apathetic, his cheeks were hollow, and his eyes sunken; no peripheral pulse was palpable, he was cyanotic and in a state of profound shock. He had tachycardia and his respiration was rapid and shallow. The diarrheal fluid was colorless and turbid, like “rice water.” An isotonic solution containing Na+, K+, Cl-, and HCO3- was infused intravenously at a rate of 100 mL/min until a strong pulse was restored and thereafter in quantities sufficient to maintain normal pulse, blood pressure, and skin turgor. When the patient stopped vomiting, a solution of similar composition but containing 2% glucose was given by mouth. Microscopic examination of the diarrheal fluid established the presence of masses of typical short, comma-shaped rods of Vibrio cholerae. A course of antibiotic therapy was started. After 24 h the fluid loss began to decline and the patient made a rapid and complete recovery. He was estimated to have lost about 20 L of fluid containing 2.8 mol NaCl.

38. Box 12-2 Toxins that Target G proteins • Vibrio cholerae produces the cholera toxin, which ADP-ribosylates GSα, inhibiting GTPase activity. Net result: cAMP is high

39. Toxins that Target G proteins • Bordetella pertussis produces the pertussis toxin, which ADP-ribosylates GIα, inhibiting nucleotide exchange. GI Pertussis toxin GI Net result: cAMP is high GI is kept off, so AC is on and cAMP levels increase

40. Drugs that Enhance cAMP • Caffeine and theophylline inhibit cAMP phosphodiesterase. cAMP phosphodiesterase Net result: cAMP is high

41. Termination of Response Pathway can be terminated at any step! • Removal of signal • Desensitization of receptor • Hydrolysis of GTP (promoted by GTPase activator proteins [GAPS]) • Degradation of 2nd messenger • Hydrolysis of phosphates

42. Fig. 12-8 Mechanisms of Desensitization Strategy #1: Receptor Level

43. Mechanisms of Desensitization Strategy #2: Downstream Effects • Morphine receptor works through GI. • Body responds to morphine by increasing AC and PKA expression.

44. Gq activates phospholipase C

45. DAG and IP3 DAG IP3

46. DAG and IP3

47. DAG and IP3

48. ~Fig. 12-10 Gq acts through DAG and IP3

49. DAG/IP3 as Second Messengers http://www.youtube.com/watch?v=2bbBrpgeheY

50. Ca2+ as Second Messenger • Variable Ca 2+ increases depending on the amount of IP3