Lecture 5 - Apoptosis and Cancer Cell Survival

oncogenes can be activated by

gene translocation or gene rearrangement

example of an oncogene that is activated by translocation

BCR/ABL; ABL is a proto-oncogene

what happens to the BCR/ABL fusion protein

the protein is stuck in the on position and thus provides a constant and continuous growth signal to the cells

a different chromosome translocation also resulted in the discovery of this gene. what happens to this gene

BCL2; the translocation results in overexpression of BCL2 genes protein products

BCL2 is was a new type of oncogene that ______ instead of ____

prevents cell death; drives cell proliferation

what are the cell phenotypes when you overexpress a typical oncogene in the presence/absence of growth factors

in +/- growth factor conditions, a typical oncogene would still drive cell proliferation even when cells should not normally proliferate

what are the cell phenotypes in the experiment where they over expressed BCL2 in the presence/absence of growth factors

- in the +growth factors, the cells proliferate

- in the -growth factors, the cells survive but do not proliferate (normal cells would just die)

BCL2 can function synergistically with _______ to induce tumors in transgenic mice

growth promoting oncogenes

research in c. elegant was able to identify

12 separate genes involved in apoptosis

apoptosis was found to occur in ___ and was enhanced by ___

tumors; radiotherapy

CED9 was a gene found in c. elegans to be involved in apoptosis... what happened when it was mutated

lots of cells that shouldn't die died; suggesting it promotes cell survival

CED9 has sequence similarity to

BCL2

expressing human BCL2 in CED9 mutant c. elegans does what

rescues the cell death phenotype from mutant CED9

BCL2 inhibits

cancer cell death

BCL2 protein family can be divided up into two groups

anti-apoptotic and pro-apoptotic

all BCL2 proteins have what type of domain

BH domains

what type of BH domain do all BCL2 family members have

BH3 domain

two proapoptotic BCL2 family proteins and where they are localized to

Bax and Bak; mitochondria

how do Bak and Bax activate apoptosis

forming a pore in the mitochondria outer membrane

once a pore is formed in the mitochondrial membrane, what happens

cytochrome c is released into the cytosol and activates a set of proteases called caspases

what happens once caspases are activated

the cell is committed to dying via apoptosis

5 anti-apoptotic proteins

-BCL2

-BCL-XL

-MCL1

-BCLW

-BFL1

3 pro-apoptotic activator proteins

-BID

-BIM

-PUMA

4 sensitizer proteins

-BAD

-NOXA

-BMF

-BIK

what happens in non-apoptotic conditions/healthy cells

-low levels of sensitizers

-prop-apoptotic activator proteins are bound to the anti-apoptotic proteins (survival proteins) which sequesters the activator proteins

-no Bax:Bak interactions

what three things can lead to high levels of sensitizers

-DNA damage

-growth factor withdrawl

-hypoxia

what are signals that activate sensitizers/ what do they do in the cell

damage signals activate transcription factors for increased expression of sensitizer proteins

sensitizer proteins have high affinity for _____ and outcompetes ______

anti-apoptotic proteins; pro-apoptotic activator proteins for binding

what happens when the activator proteins are displaced from the anti-apoptotic proteins when sensitizers bind

activators will bind to the effector proteins Bax and Bak which will form a pore in the mitochondria leading to cytochrome c release and irreversible commitment to apoptosis

what are Bak and Bax doing under normal/non-apoptotic conditions

inactive state - no pore formed

what is necessary for Bak and Bax to form a pore

pro-apoptotic activators

pro-apoptotic activators are sequestered away from Bak and Bax by

anti-apoptotic BCL2 family members

apoptotic signaling up regulates ______ which can disrupt the interaction between the ____ and ____

pro-apoptotic sensitizers; antiapoptotic proteins and pro-apoptotic sensitizers

how could you detect if cells are undergoing apoptosis

-run a blot for cleaved caspase

-look for DNA fragmentation on a DNA gel

what have cancer cells done in response to apoptosis

hijacked the normal and essential process of apoptosis

what is the apoptotic balancing act between

pro vs anti-apoptotic forces

how are BCL2 family proteins regulated (3)

-transcriptionally

-post-translational modifications

-subcellular localization

how would a BCL2 inhibitor attempt to work

the inhibitor would need to disrupt the interaction between BCL2 and the activator proteins

3 reasons why BCL2 is not a good drug target

-BCL2 is not a kinase so there is not a druggable pocket

-BCL2 is not a cell surface receptor so it is not accessible to antibody-based drugs

-BCL2 is involved in protein:protein interactions with effector proteins

at least one ______ has been found to function in every major subtype of cancer

anti-apoptotic BCL2 family member

what are BH3 mimetic drugs

the drug mimics the BH3 domain to mimic a pro-apoptotic activator bound to the anti-apoptotic proteins, leaving the pro-apoptotic activators to go and activate apoptosis

tumor lysis syndrome

resulting from tumors being lysed at the same time and all cell components are out in the organ