Cell metabolism & cancer

Question 1

what was Boveris theory of the origin of cancer cells?

Answer 1

Theodore Boveri theorised that they arose from mutations in the genetic code
(he saw aberrant nuclei in cancer cells

Question 2

what was Warburgs theory of the origin of cancer cells?

Answer 2

Otto Warburg theorised that the driver of tumorigenesis is an insufficient cellular respiration caused by insult to mitochondria.

Question 3

who was right Boveri or Warburg?

Answer 3

Both Boveri and Warburg were correct in their assumptions that genetics and metabolism respectively are important in cancer: DNA mutations alter metabolism and metabolism alters gene expression

Question 4

what is positron emission tomography imaging with 18fluoro-deoxyglucose (FDG-PET)?
how can in be used in the treatment/monitoring of cancer?

Answer 4

an imaging method that identifies locations of high glycolytic activity via FDG
Initially used in brain biology
(bladder heart and brain can also show up)

can be used to monitor the glycolytic levels arfter a particular therapy to determine - can predict long term responses of patients to cancer therapy (eg if they take up less glucose then they could have fewer tmour cells or be less glycolytic which is positive)

Question 5

what did
18FDG-PET in breast cancer subtypes
show us

Answer 5

that they is a correlation between aggressive subtypes and more glycolysis

Question 6

what is the Warburg effect?

Answer 6

The Warburg Effect is defined as an increase in the rate of glucose uptake and preferential production of lactate, even in the presence of oxygen in cancer cells
- switching of the cell from the normal respiratory pathway to aerobic glycolysis

Aerobic glycolysis in the invasive cells is greater than hypoxia-induced (aerobic) glycolysis in the non-invasive line

Question 7

what is the Pasteur effect?

Answer 7

The Pasteur effect reflects the marked difference in cellular capacity for ATP production in the presence and absence of oxygen

Question 8

in the absence of oxygen (anaerobic conditions) cells depend on what for ATP production

Answer 8

glycolysis

Question 9

ultimately what would happen if a cell didnt have ATP

Answer 9

On the cell membrane are ATP dependent sodium transporters for osmosis regulation – these need energy, if you run out of ATP the cell swells and bursts

Question 10

What is the hypothesis of hydroxia mediated selection?

Answer 10

once a tumour outgrows it blood supply and cant get enough oxygen, the cells begin hypoxia driven glycolysis. If they are genetically driven to undergo elevated glycolysis anyway then they will grow better and are the more likely cell line to survive
‘increase aerobia glycolysis makes the tumour cell more able to survive periods of low oxygen availability’ warburg 1956, gatenby&giles 2004

Question 11

why does the cancer become acidic after it becomes adapted to the low oxygen conditions and how does this help invasion?

Answer 11

because glycolysis causes lactate build up
this further changes the cell biology and drives EMT

Question 12

what changes in tumour cells result in them having high rates of anaerobic glycolysis

‘damage to respiration’ & ‘increase in the fermentation’
reversible/ irreversible

Answer 12

reversible:
- biochemical
- gene expression
- HIF1α activation

irreversible:
- FH and SDH mutations
- VHL mutations

Question 13

how/when are HIFs activated?

Answer 13

When oxygen levels are low, Hypoxia Inducible Factors (HIFs) accumulate and bind to gene promotors.
This occurs because they are no longer being ubiquitinised and degraded. In normal conditions PHDs (O2 dependent prolyl hydroxylases) hydroxylate HIF1α, which recruits pVHL, targeting HIF1α for proteosome-dependent degredation)

oxygen depletion activate HIFα increasing expression of glycolytic genes

Question 14

Whats the function of HIFs?

Answer 14

HIFs bind to the promoters of genes such as GLUT1, GLUT3, HK-2, PFK-2, PK2, LDHA, MCT4, PDK-1
These contribute to glycolysis, shut down oxidative phosphorylation in mitochondria, stop O2 & ATP consumption and increase blood supply - all things that help make the cancer more tolerant

Question 15

gives two examples of reversible regulation of glycolysis?

Answer 15

Biochemically lactate production is part of the normal process some of the pyruvate will be converted into lactate. Anaerobic glycolysis is the transformation of glucose to lactate occurs when limited amounts of oxygen (O2) are available

Gene expression and HIF1α activation: activated by depletion of oxygen levels, but when oxygen comes back PHDs will direct their degredation and the process will go back to normal. HIFs bind to the promoters of glycolytic genes

Question 16

give two examples of irreversible regulation of glycolysis

Answer 16

mutations of fumarate hydratase (FH) and succinate dehydrogenase (SDH) - causes impaired mitochondrial synthesis of ATP, fumarate and succinate accumulate which inactivates PHDs causing increased HIFα which increase glycolysis and other hallmarks of cancer

mutations in VHL - VHL is a tumour suppressor gene that targets HIFα for degredation. therefore mutations cause an accumulation of HIFα increasing glycolysis

both lead to pseudohypoxia

Question 17

what is a major difference in the control of proliferation between unicellulat and multicellular organisms

Answer 17

In a unicellular organism control of proliferation is by whether there are nutrient or not
In multicellular organisms there is always enough nutrients so proliferation is controlled by growth signals

Question 18

whats the difference in ATP production between differentiated tissue and proliferative tissue/ tumor?

Answer 18

differentiated tissue uses glucose to do oxidative phosphorylation in presence of O2 (36 ATP/mol) and anaerobic glycolysis in absence of O2 (2 ATP /mol)
tumors and proliferative tissue uses aerobic glycolysis in the presence or absence of O2 (4 ATP/mol)

Question 19

why is lactate needed?

Answer 19

to regenerate NADH

Question 20

what are the benefits of glycolysis in a proliferating cell?

Answer 20

• Glycolysis is inefficient, but it is fast, allowing rapid proliferation.
• The waste product (lactate) is recycled to glucose by the liver (Cori cycle) so is not wasted by the organism.
• This “makes sense” for the organism where localised rapid cell division is required for wound healing or an immune response. [Also embryogenesis]

Question 21

What is Pyruvate kinase M2?

Answer 21

catalyzes the final reaction of glycolysis, in which the high-energy phosphate group is transferred from phosphoenolpyruvate (PEP) to ADP to form Pyruvate, with the production of ATP
specifically found in proliferating cells (eg tumour and embryonic)

expression of PKM2 is up-regulated in most of the cancer cells

Question 22

what does the pentose phosphate pathway do for the cell

Answer 22

makes NADPH for anabolic pathways and ROS protection

in addition to helping DNA & RNA synthesis

Question 23

how do mitochondria generate harmful reactive oxygen species?

Answer 23

1. Pyruvate enters the mitochondria as Acetyl-CoA
2. This enters the TCA cycle where electrons (energy) are donated to NAD+ and FAD to generate NADH and FADH2
3. Electrons from NADH and FADH2 are passed through the electron transport chain to generate the mitochondrial membrane proton gradient that drive ATP synthase
4. Respiratory complexes leak electrons to oxygen to produce superoxide O2-

these can lead to damage to nucleic acids, lipids and proteins

Question 24

superoxide O2- production increases when ETC activity is…

Answer 24

more than ATP demand

Question 25

how are both PKM1 and PKM2 produced from one gene?

how is c-myc involved?

Answer 25

alternative mRNA splicing
(c-myc promotes the expression of spicing factors which promote PKM2 expression)

Question 26

how does Myc drive glucose and glutamine metabolism

Answer 26

Is responsible for glutaminolysis
Myc binds to the promoters and induces the expression of several key regulatory genes involved in glutaminolytic metabolism
it increases the amount of glutamine taken in by the cell and the mitochondrion

Glutaminolysis is the process by which cells convert glutamine into TCA cycle metabolites

Question 27

oncogenic growth factor signalling directly promotes ___ metabolism

Answer 27

anabolic

Question 28

how does P53 suppress glycolysis

and thus promote the pentose phosphate pathway

Answer 28

When induced by stress wild-type p53 regulate the expression & function of a set of genes which.
* suppress glucose import
* promote glucose flux into the pentose phosphate pathway
* suppress the lower stages of glycolysis
* Promotes fatty acid oxidation
* Promote oxidative phosphorylation (OXPHOS)
Mutations of the p53 gene in tumours result in loss of p53 function - so glycolysis is no longer suppressed

Question 29

how do G1/S cyclin/cdks promote glycolysis

Answer 29

• PFKFB3 is an (indirect) activator of PFK1.
  FKFB3 activation is required for glycolysis stimulation upon EGFR activation.
• PFKFB3 is targeted for destruction by APC/Cdh1
• Cdh1 is targeted for destruction by G1/S cyclin/cdks
• Hence G1/S cyclin/cdks promote glycolysis

Question 30

what is the function of pfkfb3

Answer 30

iPFK2 converts fructose-6-phosphate to fructose-2,6-bisP (F2,6BP). F2,6BP is a ‘potent’ allosteric activator of 6-phosphofructokinase-1 (PFK-1), stimulating glycolysis.

PFKFB3 is a critical regulatory enzyme of glycolysis. Its product, F-2,6-P2, is the most potent allosteric activator of PFK-1, the second of three rate-limiting enzymes for glycolysis

Question 31

what is the function of phosphofructokinase-1?

Answer 31

PFK-1 catalyzes the important “committed” step of glycolysis, the conversion of fructose 6-phosphate and ATP to fructose 1,6-bisphosphate and ADP.

Question 32

what are five therapies in development & trials
(metabolism)

Answer 32

• 2-deoxyglucose. Blocks glucose uptake by inhibiting HK2. In clinical trials. (accumulation of pyruvate which is channelled into mitochondria, creating ROS which damage the cancer cell)
• Lactate dehydrogenase A inhibitors. Lead compounds work in mouse models, by inducing ROS – no drugs yet
• MCT4 inhibitors block lactate export. Compounds in development.
• Dichloroacetate. Blocks PDK1 resulting in pyruvate flux into the mitochondria, and thus ROS. Clinical trials. Much in the press. (in pool cleaner some people have self medicated with it, read)
• Metformin; an anti-diabetic drug that inhibits complex I in the mitochondria and results in AMPK activation. Observation from diabetic patients have lead to clinical trials for cancer.

Question 33

what happens when IDH1 is mutuated/?

heterozygous and single amino acid substitutions at arginine 132

Answer 33

IDH1 normally makes alpha ketoglutarate from isocitrate, but a mutation in the gene causes it to make 2-hydroxyglutarate which is an inhibitor of aKG-dependent dioxygenenases ( includes histone and DNA demethylases) as well as HIF prolyl hydroxylases (PHDs)

causing an accumulation of HIF1alpha

Question 34

how does the proliferating cell protect against ROS and increase nucleotide synthesis

Answer 34

Growth factor stimulation can activate tyrosine kinases which inhibits Pyruvate kinase M2, lowering its activity leading to more pyruvate being channelled into lactate production via lactate dehydrogenase A. PKM2 limits ROS production by restricting pyruvate entry into the mitochondria, and increases concentration of glycolytic intermediates to fuel PPP (and serine biosynthesis). (ROS protection and nucleotide synthesis

Question 35

How does HIF make the cell more tolerant

Answer 35

HIF (hypoxia inducible factors) increases expression of genes that contribute to glycolysis (GLUT1, GLUT3), shut down mitochondria oxidative phosphorylation (PDK1), stop ATP consumption and increase blood supply (VEGF), all to make the cell more tolerant.

Question 36

how does growth factor stimulation alter PKM2 function to help tumour cells

Answer 36

Growth factor stimulation can activate tyrosine kinases which inhibits Pyruvate kinase M2, lowering its activity leading to more pyruvate being channelled into lactate production via lactate dehydrogenase A. PKM2 limits ROS production by restricting pyruvate entry into the mitochondria, and increases concentration of glycolytic intermediates to fuel PPP (and serine biosynthesis). (ROS protection and nucleotide synthesis)