autophagy Flashcards
what is macro autophagy
→ a mechanism to digest intracellular material
-> exchange in cytosol → engulfs into cell
why do cells need degredation
- homeostasis - was to rid of damaged components
- signalling - changing protein composition
- reprogramming cells
- removing damaged components
- recycling nutrients
ubiquitin system of degredation
- proteosome - certain proteins in cytosol that target degradation
- proteosome recognises cargo protein → degradation
different types of autophagy
- macroautophagy
- chaperone autophagy
- microautophagy
chaperone autophagy
receptor on surface of lysosome that recognise target proteins with spectific amino acids
microautophagy
direct engulfment of cytoplasmic cargo at a boundary membrane by autophagic tubes, which mediate both invagination and vesicle scission into the lumen
compare proteasome, macroautophagy and chaperone mediated autophagy
proteasome = no lysosomes and targets individual proteins
macroA = targets many proteins simultaneously
chaperone mediated = lower capacity, targets one protein at a time, specific subset targets
functions of macroautophagy
nutrient recycling
- upregulated during cell starvation -> smaller
cellular remodelling
- erythropoisis = loss of nucleus/other organelles
- remove sperm-derived mitochondria = rid of male mito = so dont have double
removal of damaged components
- mitochon, induction of autophagosomes etc
dietary restriction hypothesis
eating less -> live longer?
constant diet = yes e.g eat2 inhibition
fall off = no
how can autophagy target bacteria
trap bacteria in cytosol as a back up mechanism
how can autophagy be used in disease
- cancer - inhibit autophagy
- aging - boost autophagy
- pathogens - mechanisms for survival
how to make an autophagosome
- yeast - useful model organism
- one vacuole inside cell
- take mtuant where you dont have enough proteases - degradation activity is compromised - vacuole fills with vesicles - autophagosomes form
use of identifying the Atg genes
- disruption of autophagy to investigate its functions
- start on dissecting how the machinery works
- observed of autophagy in live cells
groups of autophagy machinery
- kinase - turns process on and off
- P13K
- defines where phagosomes form
- complex module
- addition of new lipids
- fuse with vesicles
- expand membrane
- snares
- recognise autophagosomes and allows fusion
what is selective autophagy
- ubiquitin tag
- adaptor proteins
- scafolding
- ubuqitn binding domain and atg8 protein domain (lipidated and encorporated into the membrane)
- adaptors → bind ubuiqitn and agt8 and drag into the membrane
Functions of autophagy:
- recycling nutrients
- damaged protein
- cellular remodelling
- intracellular pathogen removal
Functions of autophagy:
- recycling nutrients
- damaged protein
- cellular remodelling
- intracellular pathogen removal
Functions of autophagy:
- recycling nutrients
- damaged protein
- cellular remodelling
- intracellular pathogen removal
proteinopathies in neurodegeneration
- huntington and parkinsons diseases have ubuquitin aggregates found in brain
cause of huntingtons disease
- monogenic
- polyglutamine (polyQ) expansion in Huntingtin protein = amplification of gene, causing protein aggregation
- more glutamines = earlier onset
function of huntington protein
- protein/neurone maintenance
- accumulation of protein = forms aggresomes = clump
mechanisms of toxicity during protein misfolding
- loss of normal function
- toxic oligomer
- aggresomes
- adapter sequestration
- proteosomal damage
what is parkinsons
- affects dopaminergic neurones
- Main neuropathology is aggregates of α-synuclein (Lewy Bodies)
mutation causing parkinsons
a-synuclein mutations
-> α-syn normally degraded by chaperone-mediated autophagy, if not it accumulates in cytosol and blocks lysosomes from degrading
how can mitochondrial dysfunction contribute to parkinsons
- parkinsons may be caused by mitochondrial-derived oxidative damage
- damaged mitochondria can accumulate
- mitochondria are the main source of Reactive Oxygen Species (ROS)
- ROS damages cellular components
enzymes regulating mitophagy
PINK1
- mitochondrial kinase
- LOF
- linked with early onset
PARKIN
- Cytosolic E3 ubiquitin ligase = adds ubiquitin
- AR
- early onset
function of mitochondrial enzymes
- kinase and u ligase allow targeting of damaged mitochondria to allow autophagy
- without these enzymes you accumulate damaged organelles and products
- ROS:
Oxidative damage
Protein misfolding
Damaged organelles
role of autophagy in cancer
- autophagy is tumour suppressive and prevents dna damage in cells
- Autophagy is unregulated in hypoxic, nutrient-poor tumour regions
- blocking autophagy causes necrosis / apoptosis
beclin1 (Atg6) gene role
- important gene for autophagy
- gene that is monoallellically deleted in 40-75% of ovarian, breast and prostate carcinomas
what does unregulated autophagy cause
Autophagy is unregulated in hypoxic, nutrient-poor tumour regions
what does blocking autophagy cause
necrosis / apoptosis
effect of beclin 2 on surface of mitochondria
inhibition of apoptosis and interacts with beclin 1 = death
effect of beclin 1
autophagosome formation -> survival
what genes are linked to tumour survival via autophagosome formation
vps34 and UVRAG
list 2 strategies for autophatic therapy
inhibition of authophagy = increases apoptosis = prevent tumour growth in cancers
how does autophagy inhibit apoptosis
Bcl-2 inhibits apoptosis by blocking activation of Bax (and Bak) to prevent MOMP and subsequent release of cytochrome c and other apoptogenic proteins from the mitochondria
what affects autophagy activation
genes
beclin and bcl2
membrane permeabilisaiton/caspase activation
anti-oncogenic autophagy processes
cell homeostasis
damage removal
reduced ROS/genotoxicity
reducing inflammation
pro-oncogenic autophagy processes
survival during oxygen/nutrient shortage
prevention of apoptosis
survival during chemotherapy
how do issues with autophagy cause neurodegeneration
impaired autophagosome formation
disrupted cargo recognition
disrupted lysosomal function
autophagic cargo
inhibited autolysosome formation
autolysosome secretion
how does mitophagy contribute to neurodegeneration
ROS, ocidative damage, protein misfolding, damaged organelles -> inhibits mitophagy and ubuquitination of mitochondria => damaged mitochondria accumulate
how is autophagy tumour suppressive
decreased damaged organelles, protein toxicity, ROS = less oxidative stress, DNA damage, tumourigenesis
how can autophagy be manipulated in huntingtons treatment
induction of autophagy in HD cells cales accelerated breakdown of huntintin aggregates -> neuroprotection
how is a-syn normally degraded
chaperone-mediated autophagy
