apoptosis pt 2

death receptors, caspase-8, necrosis, autophagy

characteristics of tumour necrosis receptor family

• trimeric

• transmembrane receptor

• single transmembrane domain

• cytoplasmic domain has detah domain

FasL

• found on the surface of cytotoxic T cells

• extracellular ligand which binds to CD95

which pro domain does caspase-8 bind to ?

• death domain

• death effector domain

FADD 

• fas associated DD containing protein

• recruited when FasL binds to Fas receptor 

• DD will bind to DD of the receptor

• DED binds to DED of inactive caspase-8

DISC

• death inducing signaling complex

• when FADD binds to the ligand receptor complex and recruits procaspase-8

• cleavage of caspase 8 stabilises the active dimer

role of FADD in necrosis

• inhibit necrosis with caspase-8

• cleaves necrosis promoting kinases

XIAP

• inhibits caspase 3 activation

• found in high levels in hepatocytes 

role of Bid

• responds to activation of death receptors

• substrate of caspase-8. activates to activate Bax or inhibit Bcl-2

• MOMP

• SMAC released which inhibits XIAP

• caspase 3 is released

• apoptosis !

acute lymphoproliferative syndrome (ALPS)

• accumulation of T lymphocytes

• patients suffer from autoimmune conditions and lymphoid tumours

• found to be caused by inactivating mutations in CD95, FasL or caspase-8

problems with injecting FasL

• very cytotoxic

• FasL is found on many cells

• damage to liver

• death 

TRAIL receptors DR4 and DR5

• not as widespread as FasL

• over expressed in tumours

• chemotherapies may sensitise cancer cells to TRAIL

NLR

• detects different pathogens are damage signals PAMPs and DAMPs

• via the c terminal

inflammosome and caspase-1 activation

• key adaptor protein ASC contains CARD and PYD4

• PYD-PYD interactions between ASC and NLR

• central domain of NLR will release ADP, bind ATP, oligomerization

• CARD-CARD with caspase-1

function of activated caspase-1

• process inflammatory cytokines

• Pro-IL1-beta will be cleaved to active IL1-beta to be released by cells

necrotic cell death overview

• DAMPs are released

• passive

• ATP deprivation is a major cause

  • loss of osmotic potentilal, swelling, bursting

how does ischaemia/reperfusion stimulate necrosis 

• loss of blood flow, loss of ATP

• oxygen supply restored in reperfusion

  • but loss of intracellular K+, influx of calcium, inc acidification, PARP activation, opening of permeability transition pore

channels which contribute to PTP and what influences them

• voltage dependent anion channel VDAC

• adenosine nucleotide transporter ANT

• cyclophilin D in the matrix Cyp D

pH influences all of these, acidification opens them all

what inhibits PTP opening

• cyclosporine A binding to cyclophilin D and inhibitng it

• reduces damage following strokes if taken beforehand in mice

effect of over expression of CypD

• inhibits apoptosis

• overexpression of caspase-8

regulation of membrane permeability transition

• Bcl-2 blocks it

• by blocking VDAC and ANT activity

induction of apoptosis from inflammatosome

• release of reactive oxygen species

• DAMPs create inflammatory response

• inflammatory cells bring death receptor ligands

signalling for autophagy

• ATG12 complex turned on when cell senses deprivation of nutrients

• activation of Beclin1/VPS34 complex

  • lipid kinases in complex phosphorylate PIP2→ PIP3

  • ULK1 and P13 kinase complexes lead to membrane nucleation and isolation

• ATG5-12 complex activated

  • phosphatidylethanolamine conjugated on LC3 for membrane insertion

    • drives vacuole formation and elongation

what blocks the formation of new autophagosomes 

• chemical inhibition of Vps34

purposs of mTOR

• kinase which senses nutrient deprivation

• activates autophagy through ATG13 complex

• if no nutrients mTOR is turned off so ATG13 is turned on and vice versa

what does the conjugation of phosphatidylethanolamine depend on

Vps34

what inhibits mTOR activity

AMPK activation

what leads to upregulation of autophagy

• reduction of IP3

parkinsons and mitophagy

• PINK and Parkin mutated in autosomal recessive - mark defective mitochondria

• PINK accumulates and recruits Parkin

• Parkin labels with poly ubiquinon

• binds proteins then targets the damaged mitochondria to the LC3 labelled autophagosomes