Immunology Chapter 7

• 1. An enzyme that phosphorylates a protein
• 2. Threonine, Serine, Tyrosine

• 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

• 1. Dephosphorylation
• 2. May switch a signal off or on

• 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)

• 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.

• 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

• 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)

Small molecules/ions produced in response to a signal that activates another protein target or pathway stage

• 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

• 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

• 1. Motif - YXXL/IX_6-9YXXL/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)

• 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

• 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

• 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

• 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)

• 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

• 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

• 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

• 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

• 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

• 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

• 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

• 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

Mutations result in inactivation of signaling pathways for IL-2, 7, & 15 which are required for normal lymphocyte development.

• 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

• 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

• 1. Caspase - protease that cleaves proteins at aspartic acid residues; important in apoptosis
• 2. Death domain - cytoplasmic domain of the Fas protein

• 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

• 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