cell signaling Presentation varrious pathways of cell signaling .physiology.pptx

cell signalling

1. Cell signalling DR. SD.KHADHAR PASHA POSTGRADUATE- 1 st YEAR ESIC Medical College, Hyderabad

2. history

3. Alfred Goodman Gilman   American  pharmacologist  and  biochemist . He and  Martin Rodbell  shared the 1994  Nobel Prize in Physiology or Medicine  "for their discovery of  G-proteins  and the role of these proteins in  signal transduction  in cells."

4. Martin Rodbell  American  biochemist  and  M olecular endocrinologist  who is best known for his discovery of  G-proteins . He shared the 1994  Nobel Prize in Physiology or Medicine  with  Alfred G. Gilman  for "their discovery of G-proteins and the role of these proteins in signal transduction in cells.“

5. Earl Wilbur Sutherland Jr. American  pharmacologist  and biochemist . Sutherland won a  Nobel Prize in Physiology or Medicine  in 1971 "for his discoveries concerning the mechanisms of the action of hormones", especially  epinephrine , via  second messengers , namely  cyclic adenosine monophosphate , or cyclic AMP.

6. Edmond Henri Fischer was a  Swiss-American  biochemist. He and his collaborator  Edwin G. Krebs  were awarded the  Nobel Prize in Physiology or Medicine  in 1992 for describing how reversible  phosphorylation  works as a switch to activate  proteins  and regulate various cellular processes. From 2007 until 2014, he was the Honorary President of the  World Cultural Council . 

7. Robert Francis Furchgott  (June 4, 1916 – May 19, 2009) was a  Nobel Prize -winning American  biochemist  who contributed to the discovery of nitric oxide as a transient cellular signal in  mammalian  systems.

8. Louis José Ignarro   American  pharmacologist . For demonstrating the signaling properties of  nitric oxide , he was co-recipient of the 1998  Nobel Prize in Physiology or Medicine  with  Robert F. Furchgott  and  Ferid Murad .

9. Murad's key research demonstrated that  nitroglycerin  and related drugs worked by releasing  nitric oxide  into the body, which relaxed smooth muscle by elevating intracellular cyclic GMP. The missing steps in the signaling process were filled in by  Robert F. Furchgott  and  Louis J. Ignarro  of  UCLA , for which the three shared the 1998 Nobel Prize (and for which Murad and Furchgott received the  Albert Lasker Award for Basic Medical Research  in 1996). In 1999, Murad and  Furchgott  received the Golden Plate Award of the  American Academy of Achievement . He was also a member of the  National Academy of Sciences  among other notable societies.

10. introduction

11. Cell Signaling

12. Signaling events initiated by membrane-associated receptors can generally be divided into six steps: Step 1: Recognition of the signal by its receptor .

13. Step 2: Transduction of the extracellular message into an intracellular signal or second messenger .

14. Step 3: Transmission of the second messenger's signal to the appropriate effector .

15. Step 4: Modulation of the effector ..

16. Step 5: Response of the cell to the initial stimulus . Step 6: Termination of the response by feedback mechanisms at any or all levels of the signaling pathway

17. Why do cells communicate ?

18. How are signals transmitted between cells ?

19. 1.AUTOCRINE

20. 2.PARACRINE

21. 3.ENDOCRINE

22. 4.JUXTRACRINE

23. What are the first messengers ? What are second messengers? Four types of chemicals can serve as extracellular signaling molecules: Amines, such as epinephrine 2. Peptides and proteins, such as angiotensin II and insulin 3. Steroids, including aldosterone, estrogens , and retinoic acid 4. Other small molecules, such as amino acids, nucleotides, ions (e.g., Ca2+), and gases (e.g., nitric oxide)

24. How are signals transmitted across cell membranes into cell interior ?

25. What are receptors? What is downregulation? What is upregulation? What is second messengers? Types of surface receptors 1. Ligand-gated ion channels. 2. G protein–coupled receptors. 3. Catalytic receptors. 4. Receptors that undergo cleavage. Intra cellular receptor 1.Nuclear receptors.

26. 1. Ligand-gated ion channels

27. G-protein Coupled Receptor

28. G proteins G proteins are heterotrimers - α, β, and γ subunits G proteins are members of a superfamily of GTP-binding proteins This superfamily includes the classic heterotrimeric G proteins that bind to GPCRs and small GTP-binding proteins

29. The α subunit binds and hydrolyzes GTP and also interacts with “downstream” effector proteins such as “ Adenylyl cyclase” the βγ complex functioning to anchor the trimeric complex to the membrane. the βγ complex also functions in signal transduction by interacting with effector molecules distinct from those regulated by the α subunits.

30. Moreover, both the α and γ subunits are involved in anchoring the complex to the membrane. The multiple α, β, and γ subunits demonstrate distinct tissue distributions and interact with different receptors and effectors . Because of the potential for several hundred combinations of the known α, β, and γ subunits, G proteins are ideally suited to link a diversity of receptors to a diversity of effectors.

31. The heterotrimeric G protein known as Gs was so named because it stimulates adenylyl cyclase. A separate class of G proteins was given the name Gi because it is responsible for the ligand-dependent inhibition of adenylyl cyclase. The toxin from Vibrio cholerae activates Gs , whereas the toxin from Bordetella pertussis inactivates the cyclase-inhibiting Gi

32. Applied aspect Cholera toxin , a secretory product of the bacterium Vibrio cholerae, A1 fragment catalyzes the ADP ribosylation of Gαs. GTP-bound form and can activate adenylyl cyclase increase in Cl− conductance and water flow and thereby contributes to the large fluid loss characteristic of this disease. pertussis toxin , which is also an AB5 protein Pertussis toxin ADP- ribosylates G α i . This ADP- ribosylated G α i cannot exchange its GDP (inactive state) for GTP no longer release the active α i -GTP, so adenylyl cyclase cannot be inhibited Thus, both cholera toxin and pertussis toxin increase the generation of cAMP.

33. Small GTP-binding proteins More than 100 of these have been identified to date they have been divided into five groups: Ras, Rho, Rab, Arf, and Ran families. These proteins can be membrane associated (e.g., Ras) or may translocate between the membrane and the cytosol (e.g., Rho) The three isoforms of Ras ( NRas , HRas , and KRas ) relay signals from the plasma membrane to the nucleus via an elaborate kinase cascade, thereby regulating gene transcription.

34. Rho family members are primarily involved in rearrangement of the actin cytoskeleton. Rab and Arf regulate vesicle trafficking Ran regulates nucleocytoplasmic transport.

35. G-protein activation

36. RGS (for “regulation of G-protein signaling”) The RGS (for “regulation of G-protein signaling”) family of proteins appears to enhance the intrinsic GTPase activity of some but not all α subunits. RGS proteins promote GTP hydrolysis and thus the termination of signaling .

37. Downstream effects of activated G-protein α subunits

38. βγ subunits can activate downstream effectors The βγ complex then interacts with a particular class of K+ channels, increasing their permeability. This increase in K+ permeability keeps the membrane potential relatively negative and thus renders the cell more resistant to excitation. The βγ subunit complex also modulates the activity of adenylyl cyclase and phospholipase C and stimulates phospholipase A2.

39. G-Protein Second Messengers : Cyclic Nucleotides-cAMP, cGMP cAMP Adenyl cyclase cause the production of cAMP from ATP Once cAMP is formed inside the cell, it usually activates a cascade of enzymes. That is, first one enzyme is activated, which activates a second enzyme, which activates a third, and so forth. In this way, even the slightest amount of hormone acting on the cell surface can initiate a powerful cascading activating force for the entire cell.

40. in the adrenal cortex, ACTH stimulation of cAMP production results in the secretion of aldosterone and cortisol in the kidney, a vasopressin-induced rise in cAMP levels facilitates water reabsorption cAMP exerts many of its effects through cAMP-dependent protein kinase A (PKA). This enzyme catalyzes transfer of the terminal phosphate of ATP to specific serine or threonine residues on substrate proteins. PKA phosphorylation sites are present in a multitude of intracellular proteins, including ion channels, receptors, metabolic enzymes, and signaling pathway proteins.

41. The regulation of phosphorylation events One important control mechanism is the use of regulatory subunits that constitutively inhibit PKA. In the absence of cAMP, two catalytic subunits of PKA associate with two of these regulatory subunits; the result is a heterotetrameric protein complex that has a low level of catalytic activity.

42. Binding of cAMP to the regulatory subunits induces a conformational change that diminishes their affinity for the catalytic subunits, and the subsequent dissociation of the complex results in activation of kinase activity. Free catalytic subunit of PKA can also enter the nucleus, where substrate phosphorylation can activate the transcription of specific PKA-dependent genes

43. Another mechanism that contributes to regulation of PKA is the association of a PKA regulatory subunit with an A kinase anchoring protein (AKAP), which in turn binds to cytoskeletal elements or to components of cellular subcompartments cAMP as a second messenger in regulating glycogen metabolism

44. This coordinated set of phosphorylation and dephosphorylation reactions has several physiological advantages. 1.It allows a single molecule (e.g., cAMP) to regulate a range of enzymatic reactions. 2.It affords a large amplification to a small signal. cAMP is not the only second messenger used by the different hormones. Two other especially important ones are (1) calcium ions and associated calmodulin and (2) products of membrane phospholipid breakdown.

45. Hormones That Use the Adenylyl Cyclase–cAMP Second Messenger System Follicle-stimulating hormone (FSH) Luteinizing hormone (LH) Adrenocorticotropic hormone (ACTH) Thyroid-stimulating hormone (TSH) Calcitonin Human chorionic gonadotropin ( hCG ) Catecholamines (beta receptors) Angiotensin II (epithelial cells) Corticotropin-releasing hormone (CRH) Glucagon Growth hormone–releasing hormone (GHRH) Parathyroid hormone (PTH) Secretin Somatostatin Vasopressin (V2 receptor, epithelial cells)

46. one way that the cell can terminate a cAMP signal is to use a phosphodiesterase to degrade cAMP. In this way, the subsequent steps along the signaling pathway can also be terminated. another powerful way to terminate the action of cAMP is to dephosphorylate these effector proteins. Such dephosphorylation events are mediated by enzymes called serine/threonine phosphoprotein phosphatases.

47. Four groups of serine/threonine phosphoprotein phosphatases (PPs) are known: 1, 2a, 2b, and 2c. These enzymes themselves are regulated by phosphorylation at their serine, threonine, and tyrosine residues. The balance between kinase and phosphatase activity plays a major role in the control of signaling events. PP1 dephosphorylates many proteins phosphorylated by PKA, including those phosphorylated in response to epinephrine.

48. Another protein, phosphoprotein phosphatase inhibitor 1 (I-1), can bind to and inhibit PP1. Interestingly, PKA phosphorylates and induces I-1 binding to PP1, thereby inhibiting PP1 and preserving the phosphate groups added by PKA in the first place.

49. PP2a, which is less specific than PP1, appears to be the main phosphatase responsible for reversing the action of other protein serine/threonine kinases. The Ca2+-dependent PP2b, also known as calcineurin, is prevalent in the brain, muscle, and immune cells and is also the pharmacological target of the immunosuppressive reagents FK-506 (tacrolimus) and cyclosporine.

50. The substrates for PP2c include the DNA checkpoint regulators Chk1 and Chk2, which normally sense The enzymes that remove phosphates from these tyrosine residues— phosphotyrosine phosphatases (PTPs)—are much more variable than the serine and threonine phosphatases.

51. cGMP cGMP is another cyclic nucleotide that is involved in G-protein signaling events. cGMP exerts its effect by stimulating a nonselective cation channel in the retina Light activates a GPCR called rhodopsin, which activates the G protein transducin , which in turn activates the cGMP phosphodiesterase that lowers [cGMP] i . The fall in [cGMP] i closes cGMP-gated nonselective cation channels.

52. G-Protein Second Messengers: Products of Phosphoinositide Breakdown PI molecules can be phosphorylated to yield two major phosphoinositides involved in signal transduction: phosphatidylinositol 4,5-bisphosphate (PI(4,5)P2 or PIP2 phosphatidylinositol 3,4,5-trisphosphate (PI(3,4,5)P3 or PIP3 Certain membrane-associated receptors act through G proteins (e.g., Gq ) that stimulate phospholipase C (PLC) to cleave PIP2 into inositol 1,4,5-trisphosphate (or IP3) and diacylglycerol (DAG)

53. PLCs are classified into three families (β, γ, δ) that differ in their catalytic properties, cell-type–specific expression, and modes of activation. PLCβ is typically activated downstream of certain G proteins (e.g., Gq ) PLCγ contains an SH2 domain and is activated downstream of certain tyrosine kinases. Stimulation of PLCβ results in a rapid increase in cytosolic IP3 levels as well as an early peak in diacylglycerol (DAG) levels. Both products are second messengers.

54. The most important function of DAG is to activate protein kinase C (PKC), an intracellular serine/threonine kinase PKC family members PKCα, PKCβ, and PKCγ require both DAG and Ca2+ for activation PKC can also directly or indirectly modulate transcription factors and thereby enhance the transcription of specific genes

55. G-Protein Second Messengers: Arachidonic Acid Metabolites AA signaling pathways . In the direct pathway, an agonist binds to a receptor that activates phospholipase A2 (PLA2), which releases AA from a membrane phospholipid. In one of three indirect pathways, an agonist binds to a different receptor that activates PLC and thereby leads to the formation of DAG and IP3, DAG lipase then releases the AA from DAG. In a second indirect pathway, the IP3 releases Ca2+ from internal stores, which leads to the activation of PLA2 (see the direct pathway). In a third indirect pathway, mitogen-activated protein kinase stimulates PLA2.

56. The AA may follow any of three pathways to form a wide array of eicosanoids. The cyclooxygenase pathway produces thromboxanes , prostacyclins , and prostaglandins. The 5-lipoxygenase pathway produces 5- hydroxy eicosa tetra enoic acid (HETE)and the leukotrienes. The epoxygenase pathway leads to the production of other HETEs and EETs.

57. 3.Catalytic Receptors A number of hormones and growth factors bind to cell-surface proteins that have—or are associated with—enzymatic activity on the cytoplasmic side of the membrane. Here we discuss five classes of such catalytic receptors 1 . Receptor guanylyl cyclases 2. Receptor serine/threonine kinases 3. Receptor tyrosine kinases (RTKs) 4. Tyrosine kinase–associated receptors 5. Receptor tyrosine phosphatases

58. GUANYLYL CYCLASE RECEPTORS A.THE RECEPTOR GUANYLYL CYCLASE These ligands -atrial natriuretic peptide (ANP), B-type or brain natriuretic peptide (BNP), and C-type natriuretic peptide (CNP). Natriuretic peptide receptors NPRA and NPRB are membrane proteins

59. B.Soluble Guanylyl Cyclase The NO synthase (NOS) family includes neuronal or nNOS (NOS1), inducible or iNOS (NOS2), and endothelial or eNOS (NOS3). nNOS and iNOS are soluble enzymes, whereas eNOS is linked to the plasma membrane.

60. catalytic receptors serine/threonine kinases some receptors are themselves serine/threonine kinases transforming growth factor-β (TGF-β)

61. .The type II receptor first binds the ligand, and this binding is followed by the formation of a stable ternary complex of ligand, type II receptor, and type I receptor. After recruitment of the type I receptor into the complex, the type II receptor phosphorylates the type I receptor, thereby activating the serine/threonine kinase activity of the type I receptor. The principal targets of this kinase activity are SMAD proteins, which fall into three groups. The largest group is the receptor-activated SMADs (SMADs 1, 2, 3, 5, and 8), which—after phosphorylation by activated type I receptors—association with SMAD4, the only member of the second group. This heterodimeric complex translocates to the nucleus, where it regulates transcription of target genes. The third group (SMAD6, SMAD7) is the inhibitory SMADs, which can bind to type I receptors and prevent the phosphorylation of the receptor-activated SMADs.

62. RECEPTOR TYROSINE KINASES(RTK Epidermal growth factor (EGF), platelet-derived growth factor (PDGF), vascular endothelial growth factor (VEGF), insulin and insulin-like growth factor type 1 (IGF-1) fibroblast growth factor (FGF), nerve growth factor (NGF) can all bind to receptors

63. MAPK pathway A common pathway by which activated RTKs transduce their signal to cytosol and even to the nucleus is a cascade of events that increase the activity of the small GTP-binding protein Ras.

64. Tyrosine kinase–associated receptors activate cytosolic tyrosine kinases such as Src and JAK (just another kinase).

65. Receptor tyrosine phosphatases The CD45 protein, found at the cell surface of T and B lymphocytes, is an example of a receptor tyrosine phosphatase

66. 4.Nuclear Receptors Steroid and thyroid hormones enter the cell and bind to members of the nuclear receptor superfamily in the cytoplasm or nucleus This family includes receptors for steroid hormones, prostaglandins, vitamin D, thyroid hormones, and retinoic acid Activated nuclear receptors bind to sequence elements in the regulatory region of responsive genes and either activate or repress DNA transcription

67. 5. Receptors that undergo cleavage . In response to ligand binding, some transmembrane proteins undergo regulated intramembranous proteolysis  which liberates one or more fragments of their cytosolic domain that signal a cellular response by entering the nucleus to modulate gene expression.