B3.059 - Signal Tranduction Flashcards
What do kinases do
Add phosphates
What do phosphatases do
Take a phosphate from something
Whats an example of a receptor that exhibits kinase activity
Growth factor receptors
What type of receptors associate with kinases all the time (not an intrinsic part of the receptor)
Cytokines receptors
What type of receptor associates with receptors after ligand binding
Antigen receptors (B and T cell signaling)
What are JAKs
Two near identical phosphate transferring domains that have kinase activity and negatively regulate the kinase activity
What type of kinase is JAK
Tyrosine kinase
JAKs associate to what type of membrane
Proline rich region of proximal receptor
What are JAKs two domains
Box 1 and 2
What are STATS
Signal transducers and activators of transcription
How are STATS phosphorylated
By JAK, RTK, c-src
What do STATs bind to
GAS
What provides the nuclear localization signal in STATs
Coiled coil domain
What domain for JAK is critical for its ability to associate once its been phosphorylated
SH2 domain
What cytokines utilize the shared gamma common chain and what JAKs do they use
IL2R, 4R, 7R, 9R, 15R, 21R
JAK1 and 3
General model of signal transduction mediated by most class I and class II cytokines receptors
- Binding of cytokines causes dimerization of receptors and activation of JAK kinases
- Activated JAK kinases phosphorylate receptor sites and create docking sites for STAT molecules
- The phosphorylated STATs dimerize and translocate to the nucleus where they activate specific genes
What are type 1 interferons
IFN alpha and beta
JAK 1, TYK2
STAT1 and 2
Type 2 interferon
IFN gamma
JAK1 and 2
STAT1-STAT1
IL2 has a high has what type of receptor
High affinity
What JAKs does IL2 use and what STATs
JAK1, 3
STAT5a, STAT5b
IL2 receptors subfamily utilizes what subunit
Common gamma subunit aka CD132
Patients missing the gamma common chain have what
Severe X linked SCID
Patients with X linked SCID don’t produce what cytokines and what effect does that have
IL7 (don’t produce T cells) and IL15 (don’t produce NK cells)
What do X linked SCID patients have normal levels and what does that indicate
B cells, indicating a common gamma chain isn’t required for B cell production
How is specificity achieved
Unique ligand binding receptors
What phosphatases/molecules prevent phosphorylation
SHP1, SHP2 (SH2 domain) SHIP (SH2 domain) CD45 SOCS PIAS
What do SOCS and PIAS do and how does that differ from SHIPS/SHPs
They prevent further phosphorylation, while SHIPs/SHPs can dephosphorylate
What is a kinase inhibitory region and what has it
SOCS1 and SOCS3
It inhibits JAK kinase activity, prevents phosphorylation
Whats a SOCS box
Helps target the entire cytokines receptor complex for ubiquitin mediated proteosomal degradation
How does the KIR inhibit JAK kinase activity
Binds activation loop of JAK catalytic domain and functions as a pseudosubstrate
What is high SOC3 associated with
M1 macrophage polarization
What is a high SOCS1 to SOCS3 ratio associated with
M2 macrophage polarization
What does ruxolitinib do
Inhibits JAK1 and JAK2
Reduces spleen size (size of extramedullary hematopoeisis)
What disease does ruxolitinib treat
Myelofibrosis
What does Tofacitinib do
Inhibits JAK3
Interferes with IL2 and IL4 signaling
What is tofacitinib used for
Rheumatoid arthritis
Where are TLRs found
Macrophages, dendritic cells, detect a wide range of ligands
What does TL4 sense
LPS
What 2 pathways does TLR4 use
Myd88 dependent
Myd88 independent
Which TLR4 pathways is the fast pathway
MyD88 dependent
Which TLR4 pathway is the slow pathway
MyD88 independent
What does the fast pathway for TLR4 stimulate the creation of
Pro inflammatory cytokines
What does the slow TLR4 pathway stimulate the transcription of
Type 1 interferons
How does NFkB mediated gene transcription work
Requires phosphorylation of IkB by IKK complex to liberate NFkB translocate to the nucleus to regulate gene expression
What do CD4 T cells increase production of
Cytokines producers
What do CD8 T cells increase production of
Cytotoxic mediators
What is always associated with CD4/8 receptors
Lck
What is CD45
A phosphatase
What does Lck do
Phosphorylate ITAMs in CD3 chains recruiting ZAP 70 to receptor complex, which phosphorylates many linker/adaptor proteins of the distal T cell activation pathway
What are some important things that Zap 70 phosphorylate seems
LAT and Slp76 providing a scaffold for downstream signaling events
What does the PLC gamma mediated pathway increase the production of
Calcium and IL2 production
What does IL2 do
Promotes T cell growth and survival, differentiation into effector cells and memory cells and is required for T reg cells
How does PLC gamma induced increase of calcium cause induction of IL2
It generates PIP3 and DAG which activate PKC required for NFkB activation
What doe IP3 do
Opens calcium channels to allow Ca2 release from ER into cytosol, leading to aggregation of STIM 1 allowing calcium from extra cellular environment to come in and replenish stores
Describe the role of NFAT in IL2 production
NFAT is dephosphorylated by calcium entry which activates it, allowing it to enter the nucleus and activate gene transcription
What does cyclosporine/tacrolimus do
Prevents dephosphorylation of NFAT leading to suppression of IL2 transcription used for transplant patients
How are cyclosporine and Tacrolimus different in their mechanism
Tacrolimus binds FK506 blocking CaN inhibiting NFATc activation/movement to nucleus so no IL2 is produced
Cyclosporine does something similar except it binds Cpn and blocks CaN which would normally activates NFATc through dephosphorylation
What are ITIMs
Immunorecptor tyrosine based inhibitory motifs (PD-1, BTLA)
What does CTLA-4 do
Outcompetes CD28 on T cells so provides inhibitory signal
What does ipilimumab do
Targets CTLA4
What does pembrolizumab (Keytruda) do
Targets PD-1
What do T reg cells
Maintain self tolerance
Suppress self reactive lymphocytes
Where do T Regs develop
Thymus
What is the outcome of B cell activation
Production of memory cells Ig class switching Terminal differentiation into Ab secreting plasma cells
What are important in T cell dependent B cell activation
Cytokines produced by CD4 T cells
