Immunology Chapter 7

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Immunology Chapter 7
2012-03-24 22:24:12
Immune Receptor Signaling

Chapter 7
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  1. What is a protein kinase and which 3 amino acids are targeted by them?
    • 1. An enzyme that phosphorylates a protein
    • 2. Threonine, Serine, Tyrosine
  2. How does a ligand:receptor interaction activate a protein kinase
    • 1. Kinase domain may be intrinsic to the receptor or noncovalently bound
    • 2. Ligand:receptor binding causes receptor dimerization which causes kinase domains to phosphorylate each other
    • 3. Activated kinase phosphorylates downstream substrates
  3. What does a protein phosphatase do and what role can it play in signal transduction?
    • 1. Dephosphorylation
    • 2. May switch a signal off or on
  4. What are the basic features of a tyrosine kinase interacting with scaffolds and adaptors?
    • 1. Scaffolds - phosphorylated at several phosphorylation sites which recruits signaling proteins to bind to it
    • 2. Adaptors (e.g. Grb2) - bring two proteins together; binds protein (e.g. Sos) at one site (e.g. SH3) and binds kinase at another site (e.g. SH2)
  5. What are the basic aspects that regulate G proteins and how do they fit into a typical signal transduction pathway?
    • 1. Resting state - G protein (e.g. Ras) bound by GDP
    • 2. Activation - GEF's (guanine-exchange factors, e.g. Sos) catalyze exchange of GDP for GTP (on/off switch)
    • 3. Active G protein binds/recruits effectors to membrane
    • 3. Inactivation - G protein hydrolyses GTP to GDP.
  6. What are 3 ways proteins are recruited to membranes?
    • 1. Phosphorylated tyrosine kinases recruit signal proteins themselves or via adaptors or scaffolds
    • 2. G proteins can be activated and bind to membrane and recruit signal proteins
    • 3. Receptor activation can modify membrane phospholipids to recruit; PI 3-kinase phosphorylates PIP2, which produces PIP3 in the membrane, which recruits signal proteins Akt and Itk
  7. What is the role of ubiquitin conjugation in the regulation of signal transduction pathways?
    • 1. Ubiquitin ligases (e.g. Cbl) covalently binds ubiquitin to membrane proteins
    • 2. Poly-ubiquination (K48 linkages) targets for degradation by the proteosome
    • 3. Mono- or di-ubiquination targets for degradation by lysosome
    • 4. Result - signal inhibition by permanent degradation (compared to reversable phosphorylation-dephosphorylation)
  8. Define second messenger
    Small molecules/ions produced in response to a signal that activates another protein target or pathway stage
  9. How does calcium function as a second messenger and how does calmodulin function?
    • 1. Calcium is released in response to the a signal and binds/activates calmodulin via shape change
    • 2. Activated calmodulin is able to bind effector proteins
  10. What molecules comprise the CD3 component of the complete TCR?
    • 1. TCRα:β heterodimer
    • 2. 2 - ε chain
    • 3. 1 - δ chain
    • 4. 1 - γ chain
    • 5. 1 - ζ homodimer
    • 6. Each CD3 chain has one ITAM domain (signaling) and the ζ homodimer has 3/chain
  11. How does the TCR transduce a signal via ITAMs?
    • 1. Motif - YXXL/IX6-9YXXL/I
    • 2. Tyrosines become phosphorylated when ligand binds receptor which recruits signaling proteins
    • 3. Tyrosine spacing fits binding of tandem SH2-containing signaling protiens (e.g. Syk and ZAP-70)
  12. What polypeptides constitute the complete BCR?
    • 1. Light chain
    • 2. Heavy chain
    • 3. Igβ:Igα disulfide-linked heterodimer bound to the heavy chain each with a single ITAM on its cytosolic tail
  13. Describe the role of the co-receptors in T cell activation
    • 1. CD4 and CD8 co-receptors bind MHCII and MHC I respectively
    • 2. Stabilize peptide:MHC complex long enough to allow signaling
    • 3. CD4/CD8 recognition of MHC molecules causes Lck to phosphorylate ITAM tyrosines on TCR cytosolic tails
  14. What is the basic role of Lck in T cell signal transduction
    • 1. Lck kinase is constitutively associated with co-receptors (CD4/CD8)
    • 2. CD45 dephosphorylates SH2, releasing the Lck kinase domain
    • 3. CD4/CD8 recognition of MHC molecules causes Lck to phosphorylate ITAM tyrosines on TCR cytosolic tails
    • 4. ITAM phosphorylation recruits SH2 domains of signaling proteins (e.g. ZAP-70 and Syk)
    • 5. Lck phosphorylates signaling proteins which then bind substrates
    • 6. Csk phosphorylates the SH2 regions of Lck and inactivates it
  15. What is the role of PLC-γ in producing second messengers?
    • 1. ZAP-70 P LAT and SLP-76
    • 2. Gads brings SLP-76:LAT together
    • 3. Gads:SLP-76:LAT complex recruits PLC-γ
    • 4. Itk P PLC-γ activating it
    • 5. Activated PLC-γ cleaves PIP2 to generate the second messengers diacylglycerol (DAG) and inositol trisphosphate (IP3)
  16. What is the role of calcium, calmodulin and calcineurin in activating NFAT?
    • 1. IP3 opens calcium channels to allow calcium entry from ER
    • 2. Calcium binds/activates calmodulin
    • 3. Calmodulin binds transcription factor calcineurin
    • 4. Calcineurin is a phosphotase that acts on the T-cell transcription factor NFAT
  17. How does Ras stimulate the protein kinase cascade to result in AP-1 activation
    • 1. Ras initiates the Ras-MAPK cascade (a series of phosphorylations)
    • 2. Ras-MAPK cascade results in transcription of FOS gene to make c-FOS
    • 3. phosphorylated cJUN and c-FOS dimerize to form active AP1 TF
  18. Describe how PKC-θ activates the TH NFκB
    • 1. DAG recruits PKC-θ to the membrane where it P CARMA1
    • 2. CARMA1 creates scaffold with BCL10 and MALT1
    • 3. This scaffold recruits and activates TRAF-6
    • 4. TRAF6 poly ubiquitinates itself which recruits TAK1
    • 5. TAK1 P IκB causing it to ubiquitinate which targets it for degradation by the proteosome
    • 6. IκB degradation releases NFκB which activates transcription in nucleus
  19. How are the intracellular signaling pathways produced by the TCR and its co-receptor integrated?
    • 1. Lck facilitates ZAP-70 binding to TCR and CD3 and activates it
    • 2. ZAP-70 recruits PLC-γ which is activated by Itk
    • 3. Itk cleaves PLCγ into DAG and IP3
    • 4. IP3 ultimately activates NFAT
    • 5. DAG ultimately leads to activation of NFκ and AP-1
    • 6. NFAT, NFκ and AP-1 are all required transcription factors for IL-2 gene
  20. What is the function and location of CD28 and B7.1 and B7.2 molecules
    • 1. CD28 is a co-stimulatory receptor located on the the surface of naive T-cells
    • 2. B7.1 and B7.2 molecules are ligands for CD28 found on APCs such a DCs
    • 3. Binding of CD28 by B7.1 and B7.2 molecules induces CD28 phosphorylation
    • 4. This activates PI 3-kinase to produce PIP3
    • 5. PIP3 recruits PDK and Akt activating PDK to P Akt
    • 6. PIP3 also recruits Itk allowing it to P PLC-γ
  21. What are the results of BCR activation and what constitutes the B cell co-receptors
    • 1. 1. TFs NFκB, NFAT, and AP-1 induce transcription leading to cell proliferation and differentiation
    • 2. CD19, CD21, CD81
    • 3. Binding of C3dg to CD21 complexes with CD19 which causes it to be P which recruits Src kinases to initiate signaling
  22. How does CTLA-4 function and what motifs are needed for down regulation of lymphocyte activation?
    • 1. CTLA-4 binds B7.1 and B7.2 to inhibit activated T cells
    • 2. The GVYVKM motif is phosphorylated and binds co-stimulatory ligands
    • 3. The motif is unphosphorylated and binds AP-2 which removes it from the cells surface
  23. What are the 4 major families of cytokines and their basic receptor types?
    • 1. Hematopoietins - erythropoietin and growth hormone
    • 2. Heterodimeric w/common chain - IL-3, IL-5 and GM-CSF (share common β chain); IL-2, IL-4, IL-7, IL-9, IL-15 (common &gamma chain); IL-10, IL-13, IFN-α, IFN-β, IFN-γ (no common chain)
    • 3. TNF - TNF I & II, CD40, Fas, CD30, CD27, nerve growth factor
    • 4. Chemokine - CCR1-10, CXCR1-5, XCR1, CX3CR1
  24. Why does a defect in the common β chain of cytokine receptors cause X-linked severe combined immunodeficiency (SCID)?
    Mutations result in inactivation of signaling pathways for IL-2, 7, & 15 which are required for normal lymphocyte development.
  25. Describe the JAK-STAT pathway of signal transduction
    • 1. Cytokine receptors have two chains, the cytoplasmic chain binds Janus kinases (JAKs)
    • 2. Cytokine binding dimerizes the receptors which P the JAKs and the cytoplasmic domains
    • 3. Tfs (STATs) bind activated tails and are P by JAKs
    • 4. Activated STATs dimerize and translocated to nucleus to initiate transcription of lymphocytes
  26. How does the Fas-FasL interaction induce the apoptotic pathway?
    • 1. Trimeric FasL binds and trimerizes Fas
    • 2. Clustering of death domains recruits adaptor protein FADD
    • 3. FADD recruits Pro-caspases that cleave each other and activate into caspases
  27. What is a caspase and the death domain?
    • 1. Caspase - protease that cleaves proteins at aspartic acid residues; important in apoptosis
    • 2. Death domain - cytoplasmic domain of the Fas protein
  28. What are the two outcomes of the TNF-TNFR-1 interaciton
    • 1. TNF binding trimerizes TNFR, allowing it to bind TRADD
    • 2. Death - TRADD recurits FADD, which recruits caspases
    • 3. Transcription - TRADD recruits RIP and TRAF2 to induce transcription of pro-inflammatory genes
  29. What is the intrinsic pathway of apoptosis?
    • 1. Cytochrome c is present in the mitochondria of normal cells
    • 2. When programmed cell death is induced, the mitochondria swells and leaks cytochrome c which binds Apaf-1
    • 3. Apaf-1:cytochrome c complex activates pro-caspases 9 and 3 which cleaves I-CAD, releasing CAD
    • 4. CAD enters the nucleus and cleaves DNA