Signal Transduction Test 2 Flashcards
Signaling requires a ligand induced clustering of receptors called ____.
cross linking
Intergrins and Src Kinases use what kind of receptor?
Non receptor tyrosine kinase
EGF and Insulin use what kind of receptor?
RTK
Vitamin D and Glucocorticoids use what receptor?
Nuclear hormone receptor. These are lipid soluble and can pass through the membrane to the nucleus to initiate transcription of nuclear hormone target gene
Chemokines and prostaglandins use what receptor?
GPCR
Delta and delta like notch ligands use what receptor?
Notch
What kind of enzyme plays an inhibitory role?
Phosphatases
How can protein modifications impact signal transduction?
Covalent addition of Ubiquitin targets proteins for degradation or drives signal transduction in many cells.
Protein signaling molecules can also be modified by addition of lipids covalently.
What two things are modular proteins built from?
Combinations of interaction domains and catalytic domains
Tyrosine Kinase family Src (Lyn and Lck) has what two domains and what do they bind to?
SH3: proline rich peptides
SH2: phosphotyrosine
Tyrosine Kinase family Syk (Syk and Zap-70) have what domains and what do they bind?
Two SH2 which binds to phosphotyrosine
Tyrosine Kinase family Tec (Btk and Ltk) have what three binding domains and what do they bind?
SH2:phosphotyrosine
SH3: proline rich peptides
PH: binds phospholipids such has IP3
Btk tyrosine recognizes a lipid moiety called ___.
PIP3
Characteristics of Adaptor proteins?
NO catalytic activity
Contain only protein protein interaction domains
Physically link different enzymes and promote assembly of complexes of signaling molecules such as LAT and BLNK
What is LAT?
T cell linker protein for activating T cell signaling
Type of adaptor protein, it is an integral membrane protein
What is BLNK?
B cell linker, adaptor protein for B cell signaling
What is the significance of LAT and BLNK?
They are critical for B and T cell signaling, without LAT there will be no mature T cells
After phosphorylation what does LAT do?
Recruits PLC-Y and GADS
What is SLP-76?
Adaptor in T cell activation. Its proline rich and binds with SH3 domain on GADS leading to the phosphorylation of tyrosine residue
What is VAV?
Adaptor in T cell activation. Recruited by the phosphorylation of the tyrosine residue done by SLP-76. It is a GEF and will replace GDP with GTP activating enzymes/TF
Describe Adaptors in T cell activation together.
When LAT is phosphorylated it recruits PLC-y and GADS adaptor protein. THen SLP-76 associates with GADS via SH3 domain and recruits VAV after being tyrosine phosphorylated. VAV proteins are GEF’s and activate actin cytoskeletal rearrangements and transcriptional alterations
What proteins serve as signaling transducing subunits of TCR complex?
CD3 and Zeta proteins
Zeta chain has 6 ITAMs and CD3 has 2
Where are ITIMs commonly found?
FcyRIIB on B cells and myeloid cells
Describe structure of CD4.
Four extracellular Ig like domains, hydrophobic transmembrane region, highly basic cytoplasmic tail
Describe CD8 structure
Composed of two related chains called CD8alpha and CD8beta, they have a singular Ig domain, hydrophobic transmembrane region and a highly basic cytoplasmic tail
Binds MHC I and interacts with B2 microglobins
CD28 function and ligand and where its expressed?
Signal transduction, ligand is B7-1 and B7-2, expressed on APC’s
CTLA-4 function and ligand and where is it expressed?
Signal transduction (negative regulation), B7-1 and B7-2, expressed on APC’s
PD-1 function ligand and where its expressed?
signal transduction (negative regulation), PD-L1 and PD-L2, antigen presenting cells tumor cells and tissue cells
LFA-1 function ligand and where its expressed?
Adhesion, Ligand is ICAM-1, APC’s and endothelium is where its expressed
What type of TCR signals are required or positive selection of T cells in thymus?
Weak TCR signals
What does a strong TCR signal in the thymus result in?
negative selection of T cells and their death by apoptosis
What initiates the immunological synapse?
TCR recognition of MHC complex
In the immunological synapse adhesion molecules epxpressed by T cells which are ____, interact with _____ on APC’s.
LFA-1 and ICAM
In the immunological synapse what does the LFA-1:ICAM complex do?
Move away from the pMHC:TCR:CD4 complex forming the peripheral circle of molecules involved in the immunological synapse
At the same time the LFA-1:ICAM complex is moving away CD2:LFA-3 complexes and costimulatory CD28:CD80/86 move where?
Towards the pMHC:TCR:CD4 complex
Formation of pMHC:TCR:CD4 complex provides a first signal through what to get to the t cell?
through the TCR associated CD3 complex
Describe T cell activation via LCK.
Ag binds TCR and co receptor cD4 which activates LCK.
LCK phosphorylates ITAMs to activate ZAP70. ZAP70 autophosphorylates after interacting with active Zeta chain and activates LAT and PLC-y.
PLC pathway?
PKC phosphorylates ikBeta and causes dissociation from NFkB and NFkB travels to nucleus acts as transcription factor for gene production. An increase in Ca binds calcineurin and NFAT travels to nucleus as a TF for gene production
NFkB pathway?
Activation via TCR/BCR, TLR, or CD40. PKC activates IKB kinase and phosphorylation of IkB leads to ubiquination. IkB normally binds to NFkB to inhibit it and now that its free it can travel to the nucleus for gene transcription.
Where is CD28 found and what does it bind to?
On tcell and binds with CD80/86, activator of t cells
Where is CD40L found and what does it bind to?
On T cells and CD40 on APC’s, activator of t cells
CTLA-4 what does it bind to where is it found?
On T cells binds to CD80/86, inhibitor of T cells
PD-1 where is it found what does it bind to?
On T cells binds to PDL1 on APC’s , inhibitor of T cells `
What is absolutely required for induction of CTL?
CD4/TH1
In T cell co stimulation what is the primary and secondary signals?
TCR is the primary signal and CD28 binding to CD80/86 is secondary signal (co- stimulatory)
What occurs if correct co stimulation does not occur?
Anergy, T cell unresponsiveness,
Characteristics of Anergy?
Characterized by reduced capacity to synthesize IL-2. Induced by substimulatory levels of Ags in absence of CD28:CD80/86 interactions btw costimulatory receptors on T cells and APC’s. Can be overcome by exogenous IL-2.
What are the B cell co-receptors?
CD19: dominant signaling component of B cells
CD21: complement receptor 2 (CR2)
CD32: Fcy receptor type IIb (FcyRIIB)
What B cell co receptors positively regulate B cell activation?
CD21 and CD19
Also lowers the AG threshold for B cell activation
What B cell co receptor negatively regulates BCR signaling?
CD32 aka FcyRIIB, it contains an ITIM
Early steps in BCR signaling?
Signal is initiated by Ag crosslinking with the BCR and facilitated by co receptor for BCR. Lck kinase associated with Igalpha/IgBeta signaling complex is autophosphorylated. Ag binding causes conformational change in BCR ITAMs making them accessible to kinases Lyn Fyn and Blk which are Lck and Src kinases. These phosphorylate ITAMs of the IGa and IgB. Phosphorylated ITAMs provide docking site for SH2 domains of Syk Tyrosine Kinase. Syk kinase is activated by Lym, Fyn, Blk, and Lck kinase. Active Syk phosphorylates critical tyrosine residues on BLNK, and follows recrutiment of enzymes which activate PLCy2, ras, rac and Btk
TCR complex consists of what?
aB TCR non covalently linked to CD3 and Zeta proteins mediated by charged residues in transmembrane regions
In signaling what is the main function of both CD4 and CD8?
To enhance recruitment of Lck Kinase
What classes of Ig is the BCR associated with?
IgA and IgB they are disulfide linked together and non covalently associated with the BCR
What happens when PlCy and Ras are activated?
They turn on genes for cell growth differentiation and survival
What makes up the B cell c o receptor complex?
CR2-CD19-CD81 because CR2 binds to Ags through attached C3d at same times the BCR binds directly to Ag
What does C3d-CR2 binding do in b cells?
Brings CD19 in proximity to the BCR associated kinases and it becomes tyrosine phosphorylated
What are the mechanisms of CR2 Signaling?
Phosphorylated CD19 activates PI3 kinase which enhances signaling by Ag binding to BCR. PI3 kinase activates Btk and PLCy2 on inner leaflet of PM. Result of this is B cell response is greatly enhacned.
How are B cells regulated?
Through inhibitory signaling by E3 Ubiquitin ligase. They typically recruit and activate phosphatases that counter signaling events induced by Ag receptors.
What kind of binding domain and motif do inhibitory receptors of innate immunity have?
Extracellular ligand binding domain and a cytosolic ITIM motif
Key inhibitory receptors in B cells?
FcyRIIB : attenuator of acrivated B cells, DC’s and Macro
CD22: only found on B cells
If lysine 48 is ubiquinated what happens?
the protein will be targeted for proteasome
If lysine 63 is ubiquinated what happens?
Proteins are NOT targeted for degradation
