Lecture 27 Flashcards
What are the differentiating characteristics of Necrosis and Programmed Cell Death?
Necrosis typically occurs in large areas (many cells) and is initiated my injury and leads to cell swelling/lysing. The cell contents leak out leading to inflammation. These things do not happen in PCD. In PCD, which typically occurs in one cell or small clusters of cells, the cell shrinks rather than swells, and the membrane blebs but does not rupture. The shrunken cell fragments into intact pieces called apoptotic bodies that are phagocytized.
What are the biochemical characteristics of apoptotic cells?
- Extensive protein cleavage.
- DNA cleavage leading to DNA ladder effect on gel.
- Extensive protein cross-linkage via activation of
transglutaminase. - Externalization of phosphatidylserine to signal phagocytosis.
Where does the term Caspase come from?
C - because they have Cysteine in their active sites, and Asp - because they cleave proteins at C-terminus side of aspartate residues.
In what form are caspases synthesized?
They are synthesized as proenzymes so as to regulate their activity.
Which organelle plays a critical role in the “Suicide” or intrinsic PCD pathway?
The mitochondria
What are the steps in the Suicide/ INTRINSIC apoptosis pathway?
Without trophic factors, cytosolic Bad is dephosphorylated and can outcompete Bax from binding with Bcl2 on the mitochondrial membrane. That allows Bax to complex with itself forming pores in the mitochondrial membrane –> Cytochrome C can leak out of the mitochondria and combine with Apaf-1 which can then form the septameric Apoptosome using dATP and ATP –> the CARD (caspase recruitment domain) recruits Procaspase 9 –> Procaspase 9 undergoes conformational change and autocleavage to form tetrameric Caspase 9 –> Caspase 9 cleaves/activates Caspase 3
What are the steps in the Death receptor ligand EXTRINSIC Apoptosis pathway?
FasL (death signal) binds Fas (death receptor) (TNF-alpha binding TNFR1 acts the same) which trimerizes and undergoes conformational change –> Fas then binds Death Domain containing adaptor proteins (Disc) –> recruits and activates Caspase 8 –> cleaves and activates Caspase 3 –> cleaves ICAD from CAD –> CAD cleaves DNA.
How does the Perforin Granzyme Apoptosis Pathway work, and which cells are implicit to this pathway?
This pathway involves Cytotoxic T Lymphocytes (CTLs) that insert Perforin into cell membranes –> perforin forms a pore through which the CTL injects granzymes that activate Caspase 10 and directly activate Caspase 3 –> Caspase 10 also activates Caspase 3 –> ICAD cleavage from CAD –> CAD cleaves DNA.
What does Caspase 3 act on?
- ICAD (Inhibitor of Caspase Activated DNase) –> to form CAD –> CAD cleaves DNA
- Nuclear Lamins –> Fragmentation of Nucleus
- Cytoskeletal proteins –> disrupts cell signaling + transport and leads to cell fragmentation/blebbing
What is p53’s role in the Intrinsic PCD pathway?
In response to excessive cell damage, p53 acts as a TRANSCRIPTION FACTOR and upregulates production of Bax, such that there is much more Bax than Bcl2 –> Bax can complex with itself rather than binding Bcl2 –> forms pores for Cytochrome C to leak out and combine with Apaf-1, so on and so forth.
Pyroptosis is typically induced by infectious derived signals called ____ or host derived DAMPs. Canonical pyroptosis requires assembly of the ______, a scaffolding for activating caspase__ (4/5 in the non-canonical pathway) (similar to the way the apoptosome activates caspase 9). The activated caspases activate ________ D which forms membrane pores for release of pro-inflammatory cytokines IL-___ and IL-___. This leads to cell swelling, rupture, and inflammation.
PAMPs
Inlfammasome
Caspase 1
Gasdermin D
IL-1beta
IL-18
