L6 - Signal transduction of TFs Flashcards
How does cAMP transmit?
Responses to many hormones and neurotransmitters via GPCRs , Adenylate cyclase and PKA
What is the cascade of cAMP signalling?
- cAMP binds PKA and releases catalytic subunit
- PKA phosphor CREB
- CREB recuits HAT CBP (CREB binding protein)
- PKA also phosphorylates many other targets eg inhibits glycogen syn
What are the features of NF-kB?
Activated by all stimuli that elicit an immune response
Induce genes encoding many components of IS eg cytokines
How is p-65/-50 PTMd?
Unusual - sulphydration of a Cys residue
What can also stimulate DNA binding by p65-p50?
Ribosomal protein RPS3
What does IKK do?
Phosphorylates RPS3 so it translocates to nucleus to associate with p65/p50 (requires sulphydration of NF-kB)
What sequesters NF-kB proteins?
By IkB proteins with 6 ankyrin repeats
How do ankyrin repeats sequester NF-kB?
Make extensive contacts with rel homology region of NF-kB and mask nuclear localisation signal, causing cytoplasmic retention
How is the degregulation of NF-kB involved in cancer?
c-Rel gene amplified in B cell lymphomas
NF-kB2 can undergo translocation in lymphomas which truncate p100 precursor, releasing active p52
What is HTLV-1 and how does it spread?
Human T-cell leukemia virus
Transmitted through unprotected sec, contaminated blood transfusions and breastfeeding
What are the internal symptoms of HTLV-1?
Transformed T cells show constitutive nuclear activated NF-kB
Viral protein Tax binds proteasome and stimulates degradation IkB and stimulation of NF-kB1+2
Tax recrits CREB and CBP yo HTLV-1 promoter, stimulating txn
What other viruses also activate NF-kB?
HIV, HBV, EBV
What does mutation of IkB phosphoacceptor sites for IKK make?
A super repressor that is not degraded
What does the super repressor inhibit and what does this cause?
Twist, a bHLH TF required for limb development
Saethre-Chotzen syndrome (defects of hands, feet and cranium [fuse together])
What are STATs and how many are there?
Signal transducers and activators of transcription
7 in humans with unique functions
What are STATs’ function?
- Exist in cytoplasm until activator by receptors for growth factors or cytokines
- Ligand binding to receptors causes phosphor of receptor, creating docking site for STATs
- JAKS phosphorylate STATs and they dimerise and enter nucleus to activate txn
What do gene products of STATs promote?
Cell survival (survivin)
Proliferation (cyclin and c-Myc)
Angiogenesis (VEGF)
What kinds of mutations involving STATs can cause cancer?
Silencing of Tyr phosphatases that reverse STAT activation
Mutations in JAKs cause constitutive action of STAT3
Mut in STAT3 can promote dimerization
What is the positive feedback loop of STATs?
Gene product of STATs can be HIF-1
HIF-1 induces gene for pyruvate kinase M2 (PKM2)
PM2 phosphor STAT3 triggering dimerization and action
Positive feedback driving tumourigenesis
What does PKM2 do and how is this involved in cancer?
Catalyses penultimate step of glycolysis - Watburg effect (cancer cells use aerobic glycolysis to consume glucose at high rate)
What does STAT3 promote?
Migration of prostate cancer cells (activated in 67% of bone metastases)
What is a treatment for STAT3 cancer and details>
LLL12 - binds to phosphor-Tyr docking site and induces apoptosis
What are Wnts?
Small secreted proteins that bind serpentine receptor of Frizzled family at cell surface
What is beta-catenin?
Txn coactivator that is degraded in absence of Wnt signals
What happens when Wnt binds to Frizzled?
Stabilises beta-catenin which enters nucleus, binds T cell factor (TCF) and activates txn of genes eg cyclin D1 and c-Myc
What is APC@>
Adenomatous polyposis coli
Tumour suppressor that binds b-catenin with GSK3 kinase
What does GKS3 do to b-catenin?
Phosphorylates it, targeting it for ubiquitination and proteasomal degradation
How is the action of GSK3 changed by Wnt signalling?
Blocks phos of b-catenin by GSK3 so can enter nucleus
What occurs when APC mutated?
Release of B-catenin and causes colon cancers
What are nuclear receptors used for and why?
Control gradual processes because they lack the speed of kinase cascades
What do nuclear receptors typically look like?
Central DBD and C terminal ligand binding domain.
What is PPARgamma and what is it involved in?
Perozisome proliferator activated receptor
Insulin resitance, diabetes, adipocyre differentiation
What does GOF mutation in PPARgamma cause?
Promote adipocyte differentiation and obesity
How does the oestrogen receptor (ER) activate txn?
- oestrogen triggers conformation change in ER LBD, allowing dimerise and binding to ERE DNA
- ER recirts coactivators
- Acetylated histones attract BRD4 which recruits P-TEFb, which phosphorylates NELF, DSIF and pol2 CTD Ser2 allowing promoter clearance
What is the structure of bromodomains?
Bundle of 4 a-helices joined by two variable loops forming an invaginated hydrophobic pocket for binding acetylated lysine (for reading histone markers)
What are the BET subfamily?
Bromodomain and extraterminal
How is BRD4 involved in cancer?
Chomrosomal translocations drive NUT-midline carcinomas
What are the treatments for BRD4 involved cancers?
BET inhibitors (eg I-BET) selective for BET family and do not inhibit other bromodomains
How is the ER involved in cancer?
ER expression feature of 70% of breast cancers
Gene encoding ER amplified in up to 20% of breast cancers
Are ER breast cancers good or bad (relatively)?
ER+ breast cancers have bettr prognosis because of hormonal therapies
What is a successful anti-oestrogen and how does it work?
Tamoxifen
Changes conformation of helix 12 (attracts coactivators) of oestrogen to attract co-represors
What is AIB1?
Specialised nuclear HAT used by activators with oestrogen (amplified in 10% of breast cancers)
What is a therapy for prostate cancer?
Anti-androgen that binds AR and prevents action
What is CRPC and what is common in it?
Castration resitant prostate cancer
AR gene amplified in 58% of cases
