2. Cell Communication-I Pin Ling ( 凌 斌 ), Ph.D. Department of Microbiology & Immunology, NCKU ext 5632; lingpin@mail.ncku.edu.tw Reference: “Mechanisms of Cell Communication”, The Cell (5th edition), Chapter 15

3. Outline General principles of cell communication Signaling through G-protein-coupled cell surface receptors (GPCRs) and small intracellular mediators Signaling through enzyme-coupled cell-surface receptors Signaling pathways dependent on regulated proteolysis of latent gene regulatory proteins Signaling in plants Your involvement is the key to success in this lecture.

4. Features of Cell Communication 1.A single host cell (E. Coli) or multicellular organisms need to communicate with environmental cues (stimuli), then leading to appropriate responses. 2.How to do “Communication” with environmental cues? => Signaling Transduction

5. What is Signaling Transduction? Conversion of a signal from one physical or chemical form into another. The process initiated by recognition a Signal by a Sensor (receptor, kinase or enzyme) in the cell, then converting to one or more cellular responses through a series of signal transmission.

6. Inputs Responses Signals Cellular Responses (Proliferation, Differentiation, & Apoptosis) Signaling Cascades Cell Signaling Transduction Regulates Cellular Responses Human

7. Receptors Signal Transducers Effectors A simple scheme of signal transduction Molecules involved in this process, called Signaling Molecules

8. Figure 15-2 Molecular Biology of the Cell (© Garland Science 2008) Budding yeast cells responding to a mating factor (Pheromone) Budding yeast

9. Features of Cell Communication-I 1.Signal molecules bind to surface or intracellular receptors. 2.There are four types of cellular signaling: (1) Cell contact, (2) Paracrine, (3) Synaptic, and (4) Endocrine. 3.Extracellular signal molecules can act over short or long distance. 4. Extracellular signals can act slowly or rapidly to change the behavior of a target cell.

10. Cell surface vs intracellular receptors

11. Four types of intercellular signaling

12. Signaling via gap junctions

13. Strategies for long-range signaling

14. Early vs later responses to extracellular signals

15. Features of Cell Communication-II 1. Each cell is programmed to respond to the combinations of extracellular signal molecules. 2.Different cell types respond differently to the same extracellular signal molecules. 3.The same cell type can act differently depending upon signal concentration. 4.Examples of intracellular signaling, e.g. NO signaling, Nuclear receptor signaling.

16. Combinations of total signals decide the cell fate

17. Various cellular responses induced by acetylcholine

18. The same cell type can act differently upon signal concentration

19. NO functions in smooth muscle relaxation

20. Steroid hormones & other non- gaseous signal molecules

21. The Nuclear Receptor Family

22. Activation of nuclear receptors by ligand binding

23. Primary & secondary responses by nuclear receptors

24. Outline General principles of cell communication Signaling through G-protein-coupled cell surface receptors (GPCRs) and small intracellular mediators Signaling through enzyme-coupled cell-surface receptors Signaling pathways dependent on regulated proteolysis of latent gene regulatory proteins Signaling in plants

25. Three classes of cell surface receptors

27. Features of intracellular signaling pathways-I 1.Small intracellular signaling molecules => 2 nd messengers, e.g. Ca2+, cAMP, or Diacylglycerol (DAG). 2. Large intracellular signaling molecules => Signaling proteins 3. Signaling proteins act as “Molecular Switches” regulated by post-translational modifications (PTMs). 4. Signaling complex formation enhances the efficiency & specificity of the response. 5. Modular interaction domains mediate interactions between signaling proteins

28. A Signaling cascade: A surface receptor to the nucleus

29. Molecular Switches: Post-Translational Modifications

30. Signal Integration

31. Signaling complex formation by a scaffold protein

32. Signaling complex formation by an activated receptor

33. Signaling complex formation on phosphoinositoide docking sites

34. Signaling complex formation using modular interaction domains

35. Features of intracellular signaling pathways-II 1.Cells can respond abruptly or gradually to an increasing signal. 2.Intracellular signaling networks use feedback loops to regulate the process. 3.Cells can adjust their sensitivity to a signal.

36. Smoothly graded vs switchlike signaling responses-I

37. Smoothly graded vs switchlike signaling responses-II

38. Activation curves for an allosteric protein by various effector concentrations

39. A positive vs negative feedback loop

40. Positive vs negative feedback loop

41. An example of a positive feedback loop

42. Many ways to become desensitized (adapted) to a signal

43. Outline General principles of cell communication Signaling through G-protein-coupled cell surface receptors (GPCRs) and small intracellular mediators Signaling through enzyme-coupled cell-surface receptors Signaling pathways dependent on regulated proteolysis of latent gene regulatory proteins Signaling in plants

44. Signaling through G-protein-coupled cell surface receptors (GPCRs)-I 1.GPCRs are the largest family of cell-surface receptors (700 GRCRs in human). They mediate our sense of sight, smell, and taste. 2.Extracellular signaling molecules acting on GPCRs are varied in structure, including hormones, lipid mediators, & neurotransmitters. 3. All GPCRs have a common structure- a seven transmembrane peptide 4.All GPCRs use G proteins to relay the signal into the cell.

45. Signaling through G-protein-coupled cell surface receptors (GPCRs)-II 5.Some G proteins regulate the production of cyclic AMP. 6.Some G proteins activate an inosital phospholipid signaling pathway via Phospholipase C-beta (PLC-b).

46. GPCRs and G Protein GPCR G Protein:  subunit: GTPase  subunit &  subunit

47. Activation of GPCRs & G Protein

48. cAMP links some GPCR signals to gene expression

49. Some hormones act GPCR via cAMP

50. Activation of cAMP-dep protein kinase (PKA)

51. Some GPCRs activate PKC and cytosolic Ca 2+

53. Ca 2+ -mediated intracellular Signaling 1. Ca2+ functions as an intracellular mediator. 2.Ca2+ enter the cytosol from outside through various Ca2+ ion channel. 3.Ca2+ from the ER enter the cytosol through IP3 receptors or ryanodine receptors. 4.Several mechanisms keep Ca2+ in the cytosol low in resting cells. 5.Ca2+ oscillations affect a cell response. 6.Ca2+/Calmodulin-dep protein kinase mediate cellular responses (learning & memory in the nervous system).

54. Ca2+ functions as an intracellular mediator

55. Multiple ways to keep Ca2+ low in the cytosol

56. Vasopressin-induced Ca2+ oscillations in a liver cell Vasopressin GPCR PLC-  Ca2+ oscillations

57. Activation of CaM-kinase II

58. CaM-kinase II as a frequency decoder of Ca2+ oscillations

59. Smell &vision depend on GPCRs

60. A rod photoreceptor cell & its response to light

61. A rod photoreceptor cell & its response to light

62. Four major families of trimeric G proteins

63. GPCR desensitization depends on receptor phosphorylation

64. “Cell Communication II” to be continued

65. Figure 15-47 Molecular Biology of the Cell (© Garland Science 2008)