Autophagy and Rho GTPases Flashcards
(45 cards)
Describe autophagy
A mechanism to digest intracellular material. Creates a membrane which expands de novo to capture cytosol in a vesicle and digest it
Why is GFP not appropriate for tracking autophagy?
It is pH sensitive, so degrades in acidic environments, such as the lysosome
Why are organelles degraded?
Homeostasis
Removing damaged components
Signalling
Recycling nutrients
Reprogramming cells (differentiation)
Outline the basic ubiquitin/proteasome system (UPS)
Ubiquitin tags cargo proteins to be degraded in the proteasome
Describe chaperone-mediated autophagy
Lysosomal
Low capacity and degrades individual proteins
Typically turns over long-lived proteins
LAMP-2 receptor on the surface of the lysosome recognises specific target proteins by their amino acid tags
Describe the proteasome
2 outer α subunits, 2 inner β subunits
Non-lysosomal
Degrades individual, (typically) short-lived proteins
Describe microautophagy
less well understood than chaperone-mediated
lysosomes invaginate directly on the surface, allowing cargo to get sucking into the lysosome (similar to endocytosis)
What are the 4 functions macroautophagy serves?
Lysosomal
Can remove whole organisms
1. Recycling nutrients
2. Cellular remodelling
3. Removing damaged components
4. Killing intracellular pathogens
How does macroautophagy recycle nutrients?
Under starvation, it causes non-selective bulk degeneration of the cytosol to recycle nutrients for metabolism
Cells lacking autophagy die under starvation
How does macroautophagy promote cellular remodelling?
Autophagy degrades organelles which is essential for some cell differentiation, e.g removing mitochondria from sperm
How does macroautophagy removing damaged components relate to aging?
Lysosomal capacity decreases as we age
Long-lived/highly metabolic cells e.g neurons and muscle are most susceptible to age related degradation.
This pathway is boosted to reduce ageingm cancer, dystrophy and neurodegeneration
What is the dietary restriction hypothesis?
Starvation/exercise leads to autophagy and damage repair
What intracellular pathogens do macroautophagy kill?
Pathogens in the cytosol, e.g MRSA, tuberculosis and viruses
What steps are used to study autophagy?
Disrupting autophagy
Dissecting the machinery
Observing the machinery
What is the kinase complex in autophagy responsible for?
Turning the pathway on/off
How are proteins linked to autophagosome membranes?
Adaptor proteins with Atg8 interacting motif (AIM) and ubiquitin binding domain (UBD) link these.
Some proteins don’t need adaptors as they already have an AIM on them. Phosphorylation regulates this interaction
Outline the steps of autolysosome formation?
- Initiation and expansion of membrane
- Closure of membrane containing Atg8
- Fusion of lysosome
- Acidification and maturation of autolysosome
- Degradation of material
What does neuronal-specific autophagy disruption in mice cause?
Increased apoptosis
Ubiquitinated aggregates accumulating
What neurodegenerative diseases do proteinopathies have a role in?
Huntingin aggregates in Huntington’s
α-synuclein in parkinson’s
Amyloid β plaques in Alzheimers
How does huntington’s disease lead to neurodegeneration?
- > 35 CAG repeats encode a disease forming polyglutamine tract
- This misfolds and aggregates
- The proteins are ubiquitinated, forming an aggresome
- This undergoes Autophagic degradation
What possible mechanisms in Huntington’s make it toxic?
A toxic oligomer which may damage the proteasome
Aggresomes
Adaptor sequestration
Describe parkinson’s disease
Affects 1-2 per 1000
Loss of dopinergic neurons
Main neuropathology is α-synuclein aggregates (Lewy bodies) which are rarely mutated
5-10% familial cases
How do α-synuclein mutations affect autophagy?
α-synuclein is normally degraded by chaperone-mediated autophagy.
An A53T mutation in α-syn blocks LAMP2 on the lysosome, preventing autolysosome formation
What mutations cause mitochondria to accumulate in parkinson’s
PINK1- loss of function in mitochondrial kinase
PARKIN- E3 ubiquitin ligase
