4. Autophagy in cancer Flashcards

You may prefer our related Brainscape-certified flashcards:
1
Q

Which cell organelles perform degradation?

A

Degradation performed by:
- proteosomes
- lysosomes

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What needs to be degraded in cells? Why degradation mechanisms exist?

A

Need degradation for cellular homeostasis:
- toxic waste
- misfolded proteins
- regulate pathway activity (stop working when protein degraded)
- recycle molecules and cells for building blocks

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

Why are there two organelles for degradation?

A

They degrade different size proteins:
- proteosomes - barrel shaped - can’t fit large proteins in - such as protein aggregates and organelles - only degrade smaller
- lysosomes - can degrade large proteins

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What is needed for degradation in proteosomes to notice proteins meant for degradation?

A

Proteins for degradation are ubiquitinated by ubiguitin ligases -> noticed by proteosomes -> degraded

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What is autophagy?

A

Autophagy - self-degradation - cellular process in which a cell breaks down and recycles its own components, such as damaged organelles, misfolded proteins, or other intracellular debris

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What are the types of autophagy?

A

Types of autophagy:
- Micro-autophagy
- Chaperone-mediated autophagy
- Macro-autophagy (=autophagy) - the mechanism discussed in this lecture

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

Explain the mechanism of autopahgy (=macro-autophagy)

A

Autophagy (=macro-autophagy):
1) Upstream signal for autophagy induction
2) Pre-autophagosome engulfs degradation target
3) ATG8 (ex LC3) activation by fusion with a lipid
4) LC3 integration into pre-autophagosome membrane
5) Autophagosome fusion with lysosome - contains degrading enzymes
6) Degradation + recycling of nutrients

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

Explain autophagosome structure

A

Pre- autophagosome vesicle:
- double membrane
- surface proteins

Autophagosome vesicle:
+ activated ATG8 proteins (ex LC3)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

What is an autophagosome

A

Autophagosome - double-membraned vesicle that plays a crucial role in the process of autophagy - fuses with lysosome for functional degradation

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

Why is autophagosome fusion with lysosome needed for degradation?

A

Lysosomes contain digestive enzymes - inside low pH acidic - protection mechanism if aggressive degradation enzymes spilled - would not be functional in cytosol

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What was the first experiment done to investigate autophagy genes?

A

Random mutagenesis induced in yeast cells -> mutants with active / inactive autophagy -> grown in starvation media (hypothesised that autophagy is needed to survive in starvation) -> some yeats survived, others not -> first autophagy genes defined - autophagy related genes (ATG) - the ones missing in dead mutants with inactive autophagy

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

Explain the ATG proteins

A

Autophagy related genes (ATG) - genes needed to perform autophagy - 2 subfamilies of ATG8 proteins:
- LC3: LC3A, LC3B, LC3C (the ones focuse din this lecture)
- GABARAP
-> these are ubiquitin like molecules

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

What are the functions of ATG proteins?

A

ATG protein functions:
- autophagy cargo recruitment
- role in autophagosome growth and lysosome fusion

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

Explain LC3 (ATG8) protein activation

A

LC3 (ATG8) protein activation - ubiquitin-like conjugation:
1) LC3 inactive - protease cleaves off an end -> exposes glycine
2) cleaved LC3 modified by ubiquitin-like enzymes
3) PE lipid conjugated to LC3 - lipidation => LC3 activated - can integrated into pre-autophagosome membrane

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

What is used to assess lipidation of LC3 (ATG8) as a readout for autophagy?

A

Fluorescence microscopy: change in fluorescence when LC3 tagged

SDS PAGE: aactive / inactive LC3 proteins show up differently by size - active run lower

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

What are the two machinery types in involved autophagy?

A

Core autophagy mechinery: LC3 lipidation complex, ATG5 complex

Signaling autophagy machinery: Vps34 complex, ULK complex

17
Q

What are the signaling mechanisms involved in regulating ULK complex activity?

A

ULK complex - signaling autophagy machinery:
- Inhibits: mTORC1 inhibits ULK -> inhibits autophagy but mTORC1 is inhibited by am. a. starvation + anti-cancer therapy -> then ULK complex active
- Activates: AMPK activates ULK -> low energy activates AMPK -> activates ULK complex and upregulates autophagy

18
Q

Is autophogosome formation a dynamic or static process?

A

Dynamic - operates on levels - a balance must be kept in cells

19
Q

Summary of autophagy pathway

A
20
Q

What is selective autophagy?

A

Autophagy is selective - not all proteins degraded - proteins for degradation selected by receptor proteins - bring together autophagy substrates and autophagy machinery

21
Q

What are the types of substrates in autophagy?

A
22
Q

What happens to cells in autophagy absence?

A

Autophagy absence - higher cellular damage:
- ROS
- protein aggregates
- DNA damage
- inflammation
-> increased cellular damage - activation of growth suppression pathways (ex p53 tumour suppression pathways) => cell cycle arrest (senescence) / apoptosis => organ malfunction, neurodegenerative disease (brain very sensitive to autophagy absence)

23
Q

Which diseases has autophagy been associated with?

A

Cancer

24
Q

What mice experiments are employed for studying autophagy in cancer?

A

Mice experiments used:
- genetically engineered mouse models - edit autophagy genes
- xenografts

25
Q

Explain the experiment of constitutive deletion in studying autophagy importance

A

Constitutive deletion of autophagy improtant genes from the start of life

ATG7 gene deleted -> autophagy inactivation -> mice born but die 2 days after because can’t breastfeed - don’t have a milk pouch

26
Q

Explain the experiment of inducible deletion in studying autophagy importance

A

Inducible deletion of autophagy - not from beginning - deleted upon tamoxifen addition

Died without autophagy pathway from neurodegenerative disease - protein accumulation - no degradation in the brain damages the brain

27
Q

Explain how it was tested that autophagy is essential in starvation survival

A

Autophagy is essential in starvation survival - WT can survive a day without food only water - autophagy mutants die - can’t maintain glucose levels - hypoglycemia - if given external glucose without food - survive

28
Q

What is the underlying molecular cause of cancer?

A

Uncontrolled cell division:
- activation of oncogenes
- mutated tumour suppressor genes

29
Q

What are the factors influencing cancer formation?

A

Factors causing cancer:
- environmental influences
- Natural cell processes
- Inheritance
- Viruses
=> genomic mutations in oncogenes + tumour suppressing genes

30
Q

What is the role of autophagy in cancer?

A

Autophagy both prevents and supports cancer - double-edged sword:

  • Autophagy inhibits cancer - tumour suppression: in normal cells autophagy maintains cellular homeostasis - clears away waste, ROS, recycles nutrients -> absence of autophagy can induce cancer
  • Autophagy supports cancer - tumour maintenance: in cancer cells autophagy helps avoid the immune system by hiding MHC-I proteins - without autophagy in cancer cells -> suppression of growth, cell death
    => potential anti-cancer therapy
31
Q

Explain pancreatic cancer and its cause

A

Pancreatic cancer:
- most common type - pancreatic ductal adenocarcinoma (PDAC)
- treatment involved surgical resection + chemotherapy, radiotherapy
- likely caused by acinar cells - produce enzymes - acquire mutations -> become cancerous

32
Q

What is the progression like of PDAC?

A

Morphologically - loss of structure in ducts

33
Q

How does autophagy impact the development of pancreatic cancer?

A

Autophagy supports cancer development - autophagy deletion prolonged life of cancer mice - autophagy helps cancer cells evade immune system

34
Q

What exactly is the role of autophagy in cancer maintenance?

A

Autophagy promotes immune evasion by degrading MHC-I antigens on cancer cell surface - targets MHCI for lysososmal degradation - immunity can’t recognise and clear the cancer - autophagy inhibition restores MHCI levels - better cancer clearance - extends lifespan

35
Q

How can autophagy be targeted in anti-cancer therapy?

A

Autophagy inhibition - immunity activation can be used as anti-cancer therapy - shrinks tumours

36
Q

What is the current problem with targeting autophagy as anti-cancer therapy?

A

Current available autophagy inhibitors are not specific enough to only target autophagy in cancer cells - when administered also target normal cells -> problems - toxic

Current autophagy inhibitors:
- mTOR activators / inhibtors or mTOR inhibitors
- PI3K inhibitors
- lysosome inhibitors
=> all affect normal cells too - autophagy required for tissue homeostasis - further treatment development needs to make them more specific - not to have off-target effects on healthy cells