Lecture 7: Immune Receptors and Signal Transduction Flashcards
Primary T cell Deficiency (TCR Signaling)
- CD40 ligand deficiency
- CD40 deficiency
- CD3gamma deficiency
- CD8 deficiency
- ZAP-70 deficiency
- Ca++ channel deficiency
- CD25 deficiency
- STAT5b deficiency
- Itk deficiency
- DOCK8 deficiency
Nuclear receptors are intracellular transcription factors that are activated by ______ that can cross the plasma membrane
lipid-soluble ligands (estrogen, progesterone, retinoic acid)
Enzymatic phosphorylation of ___, ___, or ____ in the cytosolic portion of the receptor initiates the signal transduction
tyrosine, serine, or threonine
Specific phosphatases usually play a ____ role in signaling transduction
inhibitory
Tyrosine Kinase Families
- Src family (c-Src, Lyn, Fyn, and Lck
- Syk family (Syk and ZAP-70)
- Tec family (Tec, Btk, and Itk)
SH2 domains bind
phosphotyrosine
SH3 binds
proline-rich peptides
PH (Pleckstrin homology) domain binds (note the pleckstrin name derives from platelet and leukocyte C kinase substrate and the KSTR string of amino acids)
inositol phopholipids (PIP3) or other phosphatidylinosiol-derived lipids
SH2 domains are composed of about ___ amino acids while SH3 domains are composed of about ____ amino acids
100 (SH2 domains)
50 (SH3 domains)
The Btk tyrosine kinase recognizes a lipid moiety on the inner leaflet of the plasma membrane termed
phosphatidylinositol triphosphate (PIP3) ( note that the other Tec family kinases are Tec and Itk
Do adaptor proteins have catalytic activity
No
adaptor proteins contain only _____ interaction domains
protein-protein
adaptor proteins are molecular hubs that physically link different enzymes and promote the assembly of complexes of signaling molecules. Ex?
- LAT (linker for the activation of T cells)
- BLNK (B cell linker)
- SLP-76 (SH2 domain-containing linker protien)
- GADS (Grb-2 related adaptor protein downstream of Shc)
____ is an integral membrane protein that functions as an adaptor
LAT (lysophospholipid-Acyl-Transferase)
LAT is phosphorylated and recruits ____ and the ____ adaptor
Phosphoinositide phospholipase C (PLCgamma) and the GADS adaptor
SLP-76 (proline-rich stretch) associates with GADS via _____ domain and recruits _____ after being tyrosine phosphorylated
- SH3 domain
- VAV
_____ proteins are guanine nucleotide exchange factors (GEFs) for GTPases that activate actin cytoskeletal rearrangements and transcriptional alterations
VAV
phosphorylated ITIMs recuruit
tyrosine or inositol lipid phosphatases, which remove phosphate residues from phosphotyrosine moieties or from certain lipid phosphates and thus counteract ITAM-based immune receptor activation
Tyrosine-phosphorylated ITAMs recruit a distinct tyroxsine kinase of the _____ family, which contains tandem SH2 domains that each bind to one of the two phosphorylated YxxL/I motifs of the ITAM
Syk/ZAP-70
The inhibitory receptor _____ is found on B cells and myeloid cells
FcyRIIB
activating receptors have separate polypeptide chains for recognition and associated signaling polypeptide chains that contain cytosolic _____
ITAMs
Inhibitory receptors in the immune system typically have ____ on the cytolsolic portion of the same chain that uses its extracellular domain for ligand recognition
ITIMs
FcepsilonRI is what kind of receptor
high-affinity activating receptor for IgE
What kind of receptor is FCgammaRIIB
- inihibitory Fc receptor for IgG
- found on B cells and myeloid cells
Signaling downstream of TCRs and BCRs is characterized by a similar sequence of events consisting of:
- Receptor ligation typically involves the clustering of receptors by multivalent ligands and results in activation of an associated Src family kinase.
- receptor ligation may also induce the unfolding of the cytoplasmic tail of a polypeptide chain that is part of the receptor. The unfolding event (or conformational change) may allow previously hidden tyrosine residues of a cytosolic ITAM motif to become available for phosphorylation by a Src family kinase
- The activated Src family kinase phosphorylates available tyrosines in the ITAMs of signaling proteins that are part of the receptor complex
- The two phosphorylated tyrosines in a single ITAM are recognized by a Syk family tyrosine kinase that has tandem SH2 domains that each bind to an ITAM phosphotyrosine
- Recruitment of the Syk family kinase to the phosphorylated ITAM results in the activation of this tyrosine kinase and the subsequent tyrosine phosphorylation of adaptor proteins and enzymes that activate distinct signaling pathways downstream of the immune receptor
The TCR complex has ___ signaling chains and ___ ITAMs, and increasing numbers of ITAMs may be phosphorylated with stronger or prolonged bidning of antigen to the TCR
6 signaling chains
10 ITAMs
a coreceptor is a _________ signaling protein on a lymphocyte that can facilitate Ag receptor activation
transmembrane
The coreceptor with its signaling enzymes can
increase ITAM phosphorylation and activation fo the Ag receptor
Coreceptor on B cells
Complement receptor tyep 2 (CR2/CD21)
key inhibitory receptors in T cells
CTLA-4 and PD-1
Inhibitory receptors in B cells
CD22 and FcgammaRIIB
Prototypic costimulatory receptor on T cells
CD28 (which is activated by costimulatory molecules B7-1 (CD80) and B7-2 (CD86) ligands induced on APCs as a resulte of their exposure to microbes)
What is the difference between costimulation and coreceptors
unlike coreceptors, costimulatory receptors do not recognize components of the same ligands as do antigen receptors; signal outputs downstream of costimulatory receptors are integrated with the signals derived from the antigen receptor, and these signals cooperate to fully activate lymphocytes
The TCR complex consists of ______, ____, and ____ the association of these proteins with one another is mediated by
- The TCR complex consists of
- Alphabeta TCR non-covalently linked to CD3 and zeta proteins
- The association of these proteins with one another is mediated by charged residues in their transmembrane regions
the alpha and beta chains of the TCR have carboxyl-terminal cytoplasmic tails that are ___ to ___ amino acids long and there for are
5 to 12 amino acids long and are therefore too small to transduce signals, CD3 and zeta proteins serve as signal-transducing subunits of TCR complex
structure of CD4
- Four extracellular Ig-like domains
- a hydrophobic transmembrane region
- a highly basic cytoplasmic tail 38 amino acids long
Structure of CD8 coreceptors
- is composed of two related chains called CD8alpha and CD8beta
- CD8alpha and CD8beta have:
- a single extracellular Ig domain
- a hydrophobic transmembrane region
- a highly basic cytoplasmic tail that is about 25 amino acds long
- CD8alpha and CD8beta have:
CD8 coreceptors interact with
MHC class I and also Beta2 microglobulin
CD4 and CD8 are T cell coreceptors that bind to ________ of MHC molecules and facilitate signaling by the TCR complex during T cell activation
polymorphic regions
On ag recognition, TCR complex cluster with CD4 or CD8. CD4/CD8-associated Lck becomes active and ____________. Then ZAP-70
- Lck: phosphorylates ITAMs of CD3 and zeta chains
- ZAP-70: binds to the phosphotyrosines of the zeta chains that become self-phosphorylated and activated. It then activates (phosphorylates) various adaptor proteins such as LAT
Ligation of the TCR with Ag and CD29-CD80/CD86 costimulation results in
rapid activation fo phosphoinositide-3-kinase (PI3K)
What is the funciton of PI3K (phosphoinositide-3-kinase)
converts phosphatidylinositol bisphosphate (PIP2) into phosphatidylinositol triphosphate (PIP3)
what is the function of PDK1
PDK1, a PIP3-dependent kinase, phosphorylates and activates a downstream Akt kinase
What is the function of activated Akt
contributes to cell survival by inactivating pro-apoptotic proteins of the Bcl-2 family of apoptotic proteins
List the steps in the Ras-pathway
- upon ag recognition, Lck activates ZAP-70
- ZAP-70 phosphorylates/activates membrane-associated adaptor proteins LAT
- activated LAT binds Grb-2 adaptor protein
- Grb-2 docks the GTP/GDP exchange factor SOS
- SOS converts Ras-GDP to Ras-GTP
- Ras-GTP activates MAP kinase (MEK-1) and ERK
- ERK activates transcription factor AP-1
PLCgamma 1 in T cell signaling
- activated LAT adaptor protien binds PLCgamma-1
- The ZAP-70 activates PLCgamma-1
- activated PLCgamma-1 hydrolyzes membrane PIP2 and generates IP3 (inositol trisphosphate) and DAG (diacyl-glycerol)
- Produced IP3 stimulates an increase in cytosolic Ca2+ released from the ER
- Then, DAG activates the enzyme PKC
- Then, PKC and Ca2+ ions induce numerous cellular responses
what are the three major groups of MAP kinases in mammalian cells
- ERK (extracellular signal-regulated protein kinases)
- p38 MAP kinases
- JNK, c-Jun NH2-terminal kinases
ELK is a transcritpion factor that activates transcription of transcriptional factor ____
Fos
The p38 and JNK MAP kinases are activated by ____ from the Rho fmaily GTPases
Rac-GTP
Protein Jun in combination with Fos forms the
AP-1 early response transcription factor
The alternative Pathway of NF-kBeta pathway
- is engaged by a restricted set of cell-surface receptors
- LTbetaR
- BAFF-R
- CD40
- This pathway culminates in the activaiton of IKKalpha
- IKKAlpha directly phosphorylates RelB/p100 (NF-kBeta 2/p100)
- phosphorylation induces a partial proteolysis of p100 to p52 by the proteasome
- the p52 protein dimerizes with RelB to translocate into the nucleus
NFAT is a transcrition factor required for the expression of genes encoding
- IL-2
- IL-4
- TNF
- and other cytokines
NFAT is activated by
calcium-calmodulin-dependent phosphatase calcineurin
anergy can be induced by substimulatory levels of Ags in the absence of
- costimulatory signal provided by soluble cytokines
- interactions between costimulatory receptors on T cells and counter-receptors on APCs
when TCR engagement (signal 1) occurs in the absence of co-stimulation, calcium-mediated signals induce the activation of NFAT only. NFAT alone elicits
the expression of a distint set of anergy-inducing genes
CD3 is composed fo three polypeptide chains (__, ___, and ___) arranged in two pairs
- gamma, delta, epsilon
- two pairs ( gammaepsilon and deltaepsilon
what is Talin is a protein associated with
a protein associated with LFA-1
PKC-sigma is associated with the
TCR complex
