Lecture 31 - an alternative view by Rodwan Halimi XD Flashcards
How can knowledge of heat stress assist humans?
Hsp levels can be used as an indicator of stress.
Therapeutic uses of this can be carried out. (induce heat shock response to fight certain problems)
How can knowledge of heat stress assist humans?
Hsp levels can be used as an indicator of stress.
Therapeutic uses of this can be carried out. (induce heat shock response to fight certain problems)
What are the types of DNA damage that can occure?
Single strand breaks can occur in response to ROS or to UV radiation. This is easily repairable due to availability of the other strand to use as a template.
Double strand breaks are more severe because if unrepaired they can kill cell and if misrepaired can result in chromosomal translocation.
What are the types of DNA damage that can occure?
Single strand breaks can occur in response to ROS or to UV radiation. This is easily repairable due to availability of the other strand to use as a template.
Double strand breaks are more severe because if unrepaired they can kill cell and if misrepaired can result in chromosomal translocation.
What is the response that the cell undergoes to repair double strand breaks in DNA?
1) Detects double-strand break.
2) Cellular functions are altered and to stop cell division until break is repaired. Cell is killed if damage is severe and not repairable.
What are the types of responses that cells undergo in response to DNA double stranded damage?
Senescence (permanent cell cycle arrest)
DNA repair
Apoptosis
Tolerance
Checkpoints activation
What is the point of the DNA damage response?
Maintains genomic stability
Ensures cell cycle arrest, DNA repair. and apoptosis/survival decision making.
What are the players in the response to DNA double strand breaks?
Sensors: continuously survey chromatin for DNA damage.
Transducers: relay and amplify signal
Effectors: receive signal and repair in response to the signal. They arrest the cell cycle or cause death of the cell.
What is the MRN1/MRE11 complex?
A nuclear protein complex sensor of DNA double strand breaks; it is composed of:
MRE11, RAD50, and NBS1 and it governs the activation of downstream kinase ATM in response to DNA breaks. ATM phosphorylates histone 2Ax.
This complex is recruited rapidly and is retained at break site if histone is phosphorylated as well as other proteins such as PARP1, and MDC1.
What is ATM?
ATM is the kinase responsible for phosphorylation of histone 2Ax. It also phosphorylates various other protein substrates including Chk2.
The ATM is the gene mutated in the condition known as ataxia-telangiectasia. This is caused by a loss of kinase activity of ATM which results in ataxia.
*ATM is a nuclear protein. It has a kinase domain similar to that of the PI3 family of lipid kinases but it is not a lipid kinase
What are some complications of Ataxia - telangiectasia?
immunodeficiency
Extreme sensitivity to ionizing radiation
high rate of malignancies
How is ATM activated?
Activation requires double stranded DNA with blunt ends or short overhangs.
2nd phase of activaion requires MRN as a cofactor.
What are the advantages to sequential activation of kinases?
Amplification of the signal
Diversification of the signal
What is the function of Chk1/Chk2?
Chk1/Chk2 - nuclear protein kinase amplify DNA damage response.
What are the domains present on Chk1/Chk2?
SCD: SQ/TQ cluster domain. SQ and TQ are motifs that can be phosphorylated by PI3K kinases and ATM/ATR
FHA
Kinase domain
NLS domain localises it to the nucleus
During normal growth Chk2 is not active. How is it activated?
After DNA damage it needs to be phosphorylated at multiple sites for activation. Phosphorylation is done by the PI3K family and by ATM and ATR.
What is the result of phosphorylation of the SCD domain of Chk2?
Phosphorylation of Chk2 at the SCD domain results in dimerisation of the protein and activation of kinase domain. After activation of the kinase domain the dimers dissociate and are active.
What is the sequence of events that takes place in response to double stranded DNA damage?
1) MRN1/MRE11 detects dsDNA damage and activates ATM/ATR.
2) ATM/ATR are kinases that are similar to PI3K kinases and they activate Chk1/Chk2 by binding to their SCD domain.
3) Chk2 undergoes a conformational change and dimerises and then is activated.
4) Dimer separates and the individual monomers are active kinases which activate p53.
5) p53 is a transcription factor that can activate p21 transcription. (it is in low amounts due to Mdm2 activity.
6) p21 transcription results in p21 protein which inhibits cyclin-dependent protein kinases
7) cyclin-dependent protein kinases inhibit the cell cycle from continuing.
What is the function of p53?
p53 is a transcription factor which drives transcription of target factors. p53 is phosphorylated by Chk2 and as a result it stabilises p53 preventing it from being degraded by mdm2.
Why are normal cell levels of p53 low?
in a normal cell p53 levels are very low due to being destroyed by mdm2 via ubiquitination.
What is the function of p53?
p53 activates transcription of p21 mRNA. p21 is translated and forms p21 protein which inhibits cyclin-dependent protein kinases and as a result cell cycle is arrested.
What are some other problems that could result from DNA damage?
increased inflammation
Decreased regeneration
Impaired cellular metabolism
Suppression of endcrine function
growth retardation
insulin resistance and type 2 diabietes
