Week 11 - TNF and NFkB signalling

Question 1

What is NFkB?

Answer 1

• Nuclear Factor Kappa-light-chain-enhancer of activated B cells
• transcription factors
• inactive complex with repressors keeps it inactive in cytoplasm
• translocates to nucleus when active
• binds to kB-sites and activates genes
• for immune defence

Question 2

What is RHD?

Answer 2

• REL Homology Domain
• at N-terminus
• mediates dimerisation and DNA binding
• p65, cRel and RelB members contain Transcriptional Activation Domains (TAD)
• Inhibitory kBs (IkBs) contain ankyrin repeats
• mediate binding to RHDs

Question 3

What are IKKs?

Answer 3

• IKB-Kinase complex
• two types of inactive complexes
• dimers bound to IkB
• or dimers of unprocessed precursors (p100/5)
• phosphorylation by IKKs of serines in IkB or precursors will cause dissociation or ubiquin-mediated recognition for degradation
• canonical pathway

Question 4

What is the alternative NF-kB pathway?

Answer 4

• stimulation of TNF (*Tumour-Necrosis Factor) receptor (TNFR)
• cellular Inhibitor of Apoptosis (cIAP) and TNFR-associated factor 2 (TRAF2) and TRAF3 complex disrupted
• cIAP mediated ubiquitination of TRAF3
• NF-kB-Inducing Kinase (NIK) accumulation
• phosphorylates IKKα
• p100 phosphorylation
• ubiquitinated and processed
• p52 and RelB can translocate to nucleus

Question 5

How does TNFR1 signalling pathway induce survival?

Answer 5

• contains cytosolic Death Domain (DD)
• DD-containing TRADD interacts with DD
• recruits TRAF2 and RIPK1
• recruit IKKs
• phosphorylate IkB leading to degradation
• release of NF-kB
• translocates to nucleus
• binds to pro-survival and anti-apoptotic genes
  -induces inflammatory gene expression
• TRAF2 activates MEKK1
• starts JNK cascade
• activates AP-1
• activates pro-survival, immune resistance, and inflammatory gene transcription (with NF-kB)

Question 6

How does TNFR1 signalling pathway induce apoptosis?

Answer 6

• TNF binding causes conformational change on DD
• recuits apoptosis-related adaptor FADD
• interacts with TRADD
• DD recruits procaspase-8
• procaspase-8 and FADD contain Death Effector Domain (DED)
• induces procaspase-8 molecules to cleave each other
• generates activate caspase-8 as effector caspase
• activates executioner caspases
• initiates apoptosis
• active caspase-8 leads to cytochrome C release
• leads to caspase-3
• carries out apoptosis