Lecture 12 : Resisting cell death Flashcards
(32 cards)
Three characteristics of apoptosis
- Hormonally regulated
- Programmed
- Contributes to tumor shrinkage by therapies
Four goals of programmed cell death during development
- Elimination of supernumerary cells
- Sculpting tissues&organs
- Homeostasis
- Quality control
Give the name of the 2 classes of apoptotic stimuli and their respective Caspases initiator
- Extrinsic: Caspase 8 and 10
- Intrinsic: Caspase 9
Give the death receptor pathway (extrinsic)
Cytotoxic T lymphocytes (CTL) binds Fas death receptor (on cell membrane) which activates Casp8/10 and then activates Casp 3 (executioner Caspace)
Give the mitochondrial pathway (intrinsic)
Cell injury causes Bcl-2 family activation, mitochondria then releases cytochrome c that bind to Apaf-1 and activates Casp9 (bound to apoptosome)
Which protein released by mitochondria blocks the inhibitor of apoptosis (IAP) proteins ?
DIABLO 😈
What are the changes induced by Casp3 in apoptotic cells ?
- Endonuclease activation
- Membrane bleb (une espèce de bulle qui sort de la cellule)
- addition of ligands for phagocytic cell receptors
Give the ‘Don’t eat- me’ and ‘Eat-me’ signals ?
- Don’t eat-me: CD31
- Eat-me: complexes of PS (phosphatidylserine) with Annexin I
Give the four methods used to detect apoptosis
- Immunostaining of activated casp3
- Annexin V labelling of externalized PS
- Gel electrophoresis of the DNA
- TUNEL assay
What are the main differences between apoptosis and necrosis?
- Apoptosis: no inflammation, cells shrink, chromatin condensed, DNA fragmentation 180 bp ladder
- Necrosis: inflammation, cell swell, chromatin released, DNA fragmentation random
Are mice lacking individual caspases prone to cancer ?
No, however caspases are frequently lost or dowregulated in human cancers
What can overexpression of Bcl-2 in B cells lead to?
Lymphoma (Bcl-2 = B cell lymphoma 2)
Does Bcl-2 overexpression alone lead to cancer?
No, Bcl-2 alone prolongs cellular lifespan, proliferation caused by c-Myc upregulation is also needed
How does Bcl-2 work?
It maintains the impermeability of the mitochondrial membrane (impairs pro-apoptotic signals)
What are the different classes of BH (Bcl-2 Homology) domain proteins?
- the pro-survival class (or anti-apoptotic): it is the Bcl-2 family which has the particularity of containing 4 BH domains (BH1 to BH4).
- the pro-apoptotic class which contains the Bax family (BH123 proteins characterized by the presence of BH1, BH2 and BH3) and the BH3-only family (c’est dans le nom)
How is intrinsic apoptosis controlled (dans une cellule)?
by the ratio between pro- & anti-apoptotic BH domain proteins
How is the fate of the cell affected under stress conditions?
pro-apoptotic BH3-only proteins overwhelm anti-apoptotic factors, this excess of BH3-only proteins induces BH123 protein oligomerization -> cell death
How are BH3-only proteins activated?
they sense diverse stress signals such as UV, hypoxia, genotoxic damage, etc.
How is BH3-only mechanism used for therapy (anti-cancer drugs)? (peut etre supp si vous voulez)
development of BH3-mimics that bind BCL2-like proteins to induce apoptosis
What is promoted by defective apoptosis? What is done to avoid that? (peut etre supp si vous voulez)
- tumor recurrence and drug resistance
- combo therapies: BH3-only mimics + chemotherapy
loss of p53 impairs…
the expression of multiple pro-apoptotic genes: fax, bax, puma; and anti-survival proteins: IGF binding proteins
Ways how cancer cells increase survival signals
- upregulate Bcl-2 or IAPs (inhibitors of apoptosis)
- or hyperactivate the transcription factor NF-kB or Akt acting upstream
explain the centrality of Akt for cell survival
- Akt indirectly regulates both p53 and NF-kB
- it directly phosphorylates Bad (BH3-only) to release the survival factor Bcl-2
- it indirectly stimulates mTOR (and thus mRNA translation)
role of mTOR ( mammalian target of Rapamycin)
increase glycolysis which increases fatty acid synthesis necessary for cell growth
so it promotes cancer
