Multicellular Organisms have BIG Communication Problems

1. ? Multicellular Organisms have BIG Communication Problems Oi! We need some glucose! Hey You – divide now!!! Will you PLEASE stop dividing! Come in #7, your time is up!

2. Chapter 6 Signal Signaling

3. Learning Objectives: • 1. Some of the basic characteristics of cell signaling • 2. The types of signal molecules, receptors, molecular switches and effectors; • 3. The different signal transduction pathways; • 4. The convergence, divergence, and cross talking between different signaling pathways.

4. Cell communication…. Cell communication and cell recognition Cell recognition Cell signal…. Cell receptor…. Signal Transduction intercellular receptor signal pathway Signal pathway cell surface receptor signal pathway….. Integrin protein pathway Network signal and signal characteristics

6. Nobel prizes awarded for research in signal transduction 2001 L. H. Hartwell, R. T. Hunt, P. M. Nurse M&P key regulators of the cell cycle 2002 S. Brenner, H. R. Horvitz, J. E. Sulston M&P Apoptosis

7. 6.1 cell communication and cell recognition 6.1.1 Cell communication a Secret chemical signal b Contact-depend signal( 接触性依赖的通讯） c Gap junction signal

9. The Secret chemical Signal Endocrine signaling – signaling molecules act on target cells distant from their site of synthesis by cells of endocrine organs Paracrine signaling – signaling molecules released by a cell only affect target cells in close proximity Autocrine signaling – cells respond to substances that they themselves release, same cell type chemical synaptic Neuronal signaling

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11. 6.1.2 cell recognition • 细胞通过其表面受体与胞内信号物质选择性结合，导致胞内一系列生理生化变化，最终表现为细胞整体的生物学效应 Cells selectively bind with intercellular signal by cell surface receptor,trigger a series of physiologicaland biochemical changes , result in integrated cell effect

12. Signal transduction An extracellular signal can produce a change in the intracellular state of the cell without the initial signal crossing the membrane.

13. 6.1.3 Cell signal Classify by chemical characteristic • Hydrophobicsignal （菑类激素；甲状腺素)can transport through cell membrane ,bind with receptor in cytoplasm and nucleus to form complex • Hydrophilic signal, cannot transport through cell membrane,bind with cell surface receptor and produce second signal ,this process called signal transduction . Gaseous signal NO

15. Gaseous signal :Nitric Oxide In response to a signal from nerve cells, endothelial内皮细胞cells that line blood vessels make and release nitric oxide. Nitric oxide enters muscle cells in the vessel wall causing them to relax and dilate (扩大的) Blood flow increases and more oxygen can reach organs such as the heart. The 1998 Nobel prize was awarded to two U.S. scientists for discovering this mechanism.

16. Nitric Oxide and Carbon Monoxide ◆The nitric oxide (NO) is a major paracrine signaling molecule in the nervous, immune, and circulatory systems. NO is able to diffuse directly across the plasma membrane of its target cells. The molecular basis of NO action, however, is distinct from that of steroid action; rather than binding to a receptor that regulates transcription, NO alters the activity of intracellular target enzymes. ◆一氧化氮是可溶性的气体，产自精氨酸，在一些组织中作为局部介质起作用。NO能够引起血管壁的平滑肌细胞松弛

17. NO

18. classify by signal location • Extracellular • Receptors which have N terminal face outwards and C terminal inside the cell. • When bound to a signal molecule, changes its conformation • Signal molecules are specific to their receptors

19. Intercellular • Mostly triggered by the extracellular signal • Which converts the extracellular into an intracellular signal • Eg. - G protein, GTPase, cAMP, Ca++, Kinases, phosphatases and many more • Also called as second messengers

20. 6.1.4 Second messenger and molecular switch Second messenger: Primitive signal bind with receptor and then trigger second messenger （ cAMP,IP3,DG,)

21. 第二信使至少有两个特征: 是第一信使同其膜受体结合后最早在细胞膜内侧或胞浆中出现，仅在细胞内部起作用的信息分子 能启动或调节细胞内稍晚出现的反应。 目前公认的第二信息有cAMP、DG、IP3、cGMP

22. Molecule switch protein Protein kinase phosphorylation let it open ， Dephosphorylation let it close Protein+GTP=active Protein+GDP=INactive

24. Communication by extracellular signals steps : 1)Synthesis and release of signaling molecules by the signaling cell 2) Transport of the signal to the target cell 3) detection of the signal by a specific receptor protein 4) And change in cellular metabolism or gene expression triggered by the receptor-signaling molecule complex 5) Removal of the signal, often terminating the cellular response

25. 6.2 Cell receptor Receptor: recognition and selectively bind with ligand signal,extracellular siganl change into intercellular physical or chemical signal，triggered a series of process，result in biological effect Membrane Receptor intracellular receptor cell surface receptor Nucleus receptor Cell receptor

26. Receptors • Signal molecules that do not enter the cell bind to cell-surface receptors. • Signal molecules that enter the cell bind to intracellular receptors.

27. intracellular receptor • Transmembrane receptors • That span the thickness of the plasma membrane • Intracellular domain and extracellular domain • Signal trasduction/through small molecules (Ca++) – Ion Channels

28. intracellular receptor

29. Three classes of cell-surface receptors • Ion-channel-linked receptors open an ion channel in response to the signal molecule. • G-protein-linked receptors activate an intracellular G-protein that in turn activates intracellular enzymes. • Enzyme-linked receptors directly activate a membrane bound enzyme.

30. Nuclear receptors • Soluble proteins localised within the cytoplasm or the nuceloplasm • Ligand activated trascription activators • Hormone regulation • Steroid receptors (located within cytosol

31. Defining a Receptor • Specificity – a receptor must be able to distinguish between often closely-related signals • High affinity – signals are often present in low concentrations – effective receptors can often detect nM to pM concentrations • Saturability– a cell has a finite number of receptors and, thus there is a limit to the number of ligand molecules a cell can bind

32. Reversibility – ligand-receptor association is not covalent – as the ligand concentration drops the complex can dissociate • Coupling – the receptor transfers a signal from ligand to cell

33. Coping with Multiple Signals – Receptor ‘Crosstalk’ Suppose a cell receives two signals. Signal A inhibits proliferation, whilst signal B stimulates proliferation… A B kinase …which phosphorylates and inactivates the receptor for signal B - result – no proliferation Signal A activates a kinase…

34. If ‘crosstalk’ only works in one direction (A to B) then signal A will be dominant • If ‘crosstalk’ works in both directions, the outcome will depend on several factors e.g. Timing of signal perception Relative receptor density Relative signal concentration

35. 6.3 intercellular receptor signal pathway • 亲脂小分子与细胞内受体结合 细胞内受体的本质是激素激活的基因调控蛋白，构成细胞内受体超家族

36. steroid hormone(甾类激素)signal pathway primary responsesecondary response

37. A Ion-channel-linked receptors open an ion channel in response to the signal molecule. B G-protein-linked receptors activate an intracellular G-protein that in turn activates intracellular enzymes. C Enzyme-linked receptors directly activate a membrane bound enzyme. 6.4 cell surface signal pathway

39. Types of ion channel A (ion-channel-linked receptor)

40. B G protein -linked signal pathway • 1994 Nobel prize. Discovery of G-protein coupled receptors and their role in signal transduction • 43,409 articles in Medline that mention G proteins. • G  ＋GTP激活态（open ） • G  ＋GDP失活态（close

41. G-protein sructure • G-protein-coupled receptors • C-AMP • G-protein-linked signal pathway

42. 4 subtypes  • binds GTP • activation of 2nd mess.    • less variability • also activates 2nd mess.   G-protein sructure （G-protein subunits）

43. Gq G12/13 Gi/o Gs         G-protein subtypes • inhibition of cAMP production • inhibition of Ca2+ channels • activation of GIRK K+ channels • mediates signalling between GPCRs and RhoA (GTPase) • function under investigation • increased synthesis of cAMP • activation of Ca2+ and K+ channels • activation of PLC leading to • activation of PKC (DAG) • intracellular Ca2+ release (IP3)

44. 1. Basic facts about G proteins • Each G-protein consists of 3 sub-units, sub-units can be together or separated. • Each G-protein has a binding site that can be occupied by either GDP or GTP. • A G-protein is said to be inactive when it is bound to GDP. • A G-protein is said to be active when it is bound to GTP.

45. Small GTP-binding proteins • Ras (growth factor signal cascades). • Rab (vesicle targeting and fusion). • ARF (forming vesicle coatomer coats). • Ran (transport of proteins into & out of the nucleus). • Rho (regulation of actin cytoskeleton)

46. L Effector  G  Signal G-proteins exterior cytosol

47. G-protein-coupled receptors 与配体结合 Extracellular -NH2 e3 e2 -S-S- e1 TM1 TM2 TM3 TM4 TM5 TM6 TM7 D R Y C2 C1 C3 Cytoplasmic G蛋白作用部位 COOH-

48. cAMP ATP  cAMP + PPi

49. Cyclic AMP • Cyclic-AMP is suited to be a transient signal. • Synthesis & degradation of cAMP are both spontaneous, but enzymes are required to synthesize these reactions. • Enzymes that synthesize and degrade cAMP are regulated.

50. G-protein-linked signal pathway • C-1 CAMP signal pathway • C-2 磷脂酰肌醇信号通路(Double messenger pathway)