BIO135 Hedgehog Notes.txt

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BIO135 Hedgehog Notes.txt
2012-05-17 05:53:50
BIO135 Hedgehog Notes

BIO135 Hedgehog Notes
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  1. In the notch pathway, ___ and Jagged are ___.
    Delta, ligands
  2. Notch is composed of ___.
    • NECD - Notch extracellular domain
    • transmembrane domain
    • NID - Notch intracellular domain
  3. ___ cleaves the NECD from the ___.
  4. What is ADAM?
    A desintegrin and metalloprotease
  5. The NICD makes its way to the ___ and generally results in ___.
    • nucleus
    • transcription, cell division, differentiation
  6. Hh are ___, a ___.
    • ligands
    • family of secreted proteins
  7. Hh generally functions in ___.
  8. In adult cells Hh can lead to ___.
  9. Hh homologues in vertebrates include ___.
    sonic, desert, Indian Hh
  10. What is the receptor for Hh?
  11. What are the receptors for Hh in mammals?
    • Hip1
    • Patched1
    • Patched2
  12. Besides Patch and Hip, what else is needed for Hh pathway activation?
  13. The ultimate target of Hh in the fruitfly is ___, a ___.
    • cubitus interruptus (Ci)
    • transcription factor
  14. What vertebrate homologue most closely resembles Drosophila Hh?
  15. How do Shh, Dhh, and Ihh differ?
    Typically by potency - Shh>Ihh>Dhh
  16. What role in develoment does Hh play?
    cellular proliferation, growth, and axon path finding
  17. What are examples of human developmental disorders from Hh?
    • Holoprosencephaly
    • Greig cephalopolysyndactyly syndrome
    • Pallister-Hall Syndrome
    • Gorlin's syndrome
  18. What are some cancers triggered by malfunctioning Hh?
    • Basal cell carcinoma
    • Rhabomyosarcoma
    • Medulloblastoma
    • Small cell lung cncer
    • Pancreatic cancer
  19. What are some components of the Hh pathway?
    • Patch(Ptc) - membrane receptor
    • Smoothened (Smo) - intermembrane protein
    • Intracellular Hh Signaling complex (HSC)
  20. Describe Patch.
    • Membrane receptor which activates Smo when bound to Hh.
    • After binding, Ptc levels decrease as a result of endocytosis
  21. In vertebrates, Ptc does not have ___, so it needs ___.
    • Dimer
    • Hip
  22. Describe Smoothened.
    Intermembrane protein that when activated relays signals to HSC
  23. In vertebrates, Smo is always ___.
    at the cell membrane
  24. Describe HSC.
    • Coastal 2 (Co2) - kinesin-related protein
    • Fused (Fu) - Ser/Threo kinase
    • Supressor of fused (Su/Fu)
    • Cubitus Interruptus (Ci)
  25. What are three Ci homologs as activators in mammals?
    Gli1, Gli2, Gli3
  26. Since Gli acts only as an activator, it does not get ___.
  27. What happens to Ci when there is no Hh?
    HSC truncates Ci which becomes a repressor
  28. What happens when Hh binds to Ptc?
    Production of Ci which becomes an activator
  29. In the Drosophila wing imaginal disc, Ci is truncated where?
    In all but cell fate 1 nearest the posterior
  30. In the Drosophila wing imaginal disc, Hh concentration results in activation where?
    In all but cell fate 5 (nearest the Anterior) which results in repressor.
  31. In the Drosophila wing imaginal disc, how does Hh concentration affect expression?
    [Hh] is proportional to activation
  32. What is involved in Hh processing?
    • Autocleavage
    • Binding of cholesterol to C end
    • Addition of palmitate to amino terminus
  33. Describe the binding of Hh to cholesterol.
    • Critical for target cell intake
    • Critical for signal transduction after Hh binds to Ptc
    • If binding is inhibited, Hh doesn't work
  34. In the absence of Hh, Ptc ___.
    blocks the phosphorylation and stability of Smo.
  35. What type of receptor does Smoothened have?
    G protein coupled receptor
  36. When there is no Ptc, ___.
    Smo is found in endosomal vesicles
  37. Upon Hh binding to Ptc, ___.
    Smo is released and localizes to the cell membrane
  38. Smo multimers may be required for ___.
    high level signaling
  39. With Hh present, Ci__ is processed to ___ or ___.
    • 155
    • Weak activator - Ci^act
    • Strong activator - Ci*
  40. If no Hh is present, Ci__ is formed.
  41. How is Ci phosphorylated?
    • PKA
    • Glycogen synthase Kinase 3-beta
    • Casein Kinase 1-gamma
  42. Upon phosphorylation, Ci is ___ by ___, a ___.
    • ubiquitinated
    • Slimb (supernumerary limbs)
    • proteosome for cleavage
  43. Describe Coastal 2 (Cos2)
    • Possibly a microtubule-motor
    • Interacts with Smo
    • Responsible for moving Smo
  44. How do Cos2 and Smo interact?
    • Cos2 binds Fu to Smo
    • Their interaction is critical for hh pathway signalling
  45. Where does Cos2 move Smo?
    • cell membrane upon Hh pathway activation.
    • Intracellular vessicles in the absence of Hh ligand
  46. Describe Fused (Fu)
    • Has kinase activity, i.e. might phosphorylate Cos2 and Su(Fu) upon Hh pathway activation.
    • Binds to Cos2 and Su(Fu) via carboxy terminus domain
  47. Describe Suppressor of Fused
    • May be antagonistic to Fu
    • No a.a. homology to known proteins
    • Binds Fu and Ci, but not Cos2
  48. What evidence is there that Su(Fu) and Fu might be antagonistic?
    Su(Fu)- and Fu- flies yield a wt phenotype
  49. What are possible functions of Su(Fu)?
    • May inhibit Ci activation
    • Nuclear translocation of Ci
    • Transcriptional regulation in vertebrates
  50. Describe Hh pathway at no/low [Hh].
    • Ptc on cell membrane repressing/sequestering Smo at vesicle with HSC-A inactive.
    • HSC-R on MT picking up vesicle leading to truncated Ci^75 by Su(Fu).
    • Ci^75 to nucleus as repressor
  51. Describe Hh pathway at medium [Hh].
    • Hh binds Ptc at cell membrane permitting Smo/HSC-A to go to cell membrane
    • HSC-R not at MT
    • HSC-A allows Ci^act into Nucleus for low activation with possible low amount of Ci^75.
  52. Describe Hh pathway at high [Hh].
    • Hh sequesters Ptc to vesicle permitting Smo Multimer/HSC-A to go to cell membrane
    • Fu phosphorylates Cos2/SuFu
    • SuFu leaves HSC
    • Cos2 drives Ci to Smo
    • HSC-R not present/inactivated.
    • HSC-A allows Ci* to be processed untruncated into Nucleus by SuFu for high activation
  53. Research shows that Hh signalling malfuction is responsible for:
    • Formation of tumors
    • Survival of tumors
  54. In mammals, absence of Hh leads to ___.
    • Gli forms MT-attached complex with Fu and SuFu
    • Gli remains in cytoplasm
  55. In mammals, if Hh is present, ___.
    • Hh binds to Ptc
    • Smo is activated (no longer supressed)
    • Processing of Gli is activated
    • Gli is translocated to nucleus
  56. In mammals, the negative feedback regulators in the Hh pathway are ___.
    Ptch, Hip, Gli
  57. What genes are for cell proliferation?
    • Cyclins D1 and D2 (mammalian) -> mitosis
    • cMyc
  58. What are three target proteins?
    • Cyclin B - Mitotic P Factor (MPF) - nuclear translocation
    • P21 inhibition - tumor supression
    • PDGF pathway activation (MAPK) - cell division
  59. What are two types of genetic problems w.r.t. cancer?
    • LOF for tumor supression - Ptc and SuFu
    • Overexpression of oncogenes - Shh and Smo
  60. LOF of SuFu leads to ___.
  61. LOF of Ptc1 leads to ___.
    cell nevus carcinoma
  62. Heterozygous Ptc mice ___.
    develop tumors
  63. Blocking Smo blocks ___.
    binding of Hh
  64. What should be inhibited for cancer treatment?
    Smo, Gli
  65. What are inhibitors of Smo?
    • Cyclopamine - binds to Smo, but difficult to synthesize and toxic
    • KAAD - modified cyclopamine - less toxic
  66. How do you inhibit Gli?
    • Forskolin - PKA activator - used in different pathways as well
    • RNAi - Not feasible for treatment