unintentional cell death
necrosis
requires ATP, changes in gene expression, and proteins synthesis
apoptosis
Progression of Apoptosis: cell shrinkage and rounding then chromatin undergoes condensation forming patches against the nuclear envelope called
pyknosis
Progression of Apoptosis: nuclear envelope becomes discontinuous and DNA is fragmented and this is called
karyorrhexis
Progression of Apoptosis: nucleus breaks into discrete chromatin bodies due to degradation of DNA and the cell membrane shows irregular bud called
blebs
Progression of Apoptosis: cell breaks apart into several vesicles called what before being phagocytised by neighboring cells
apoptotic bodies
apoptosis role during development
tissue remodeling (digit formation), elimination of transitory organs and tissues, nervous system formation
three main component of apoptotic pathway
regulators, adapters, effectors (caspases)
inhibit apoptosis or initiate apoptotic pathway
regulators
bind to procaspases and either facilitate proteolytic of procaspases to active caspases directly or by cause the aggregation of procaspase resulting in self activation
adapters
serve to execute apoptosis by targeting various cellular components and enzymes
effectors (caspases)
how are procaspases activated
they are activated by proteolytic cleaving hence forming active caspase (large and small subunit) and prodomain(cleaved off) then a bunch of active caspases can activate other procaspases
stimuli that activate apoptosis
Genotoxic damage Viral infection Microtubule disruption ER damage Hypoxia Hypoglycemia Reactive oxygen species Mitochondrial damage Death receptor activation Growth factor withdrawal Anoikis (detachment from ECM)
intrinsic pathway is responsible for eliminating cells in response to
genotoxic damage, mitochondrial damage, absence of growth factors, loss of substrate adhesion etc
what is the intrinsic pathway of apoptosis
cell and DNA damage activate protein kinases that phosphorylate and activate p53 (TF)
p53 binds to DNA and causes transcription of BAX and cell cycle inhibitor p21
BAX inserts into mito membrane and causes release of cytochrome C from mito
cytochrome C binds to the adapter protein Apaf-1 causing aggregates and binds procaspase (apoptosome complex)
procaspases are cleaved to form active form –> caspases
extrinsic pathway is responsible for elimination of
unwanted cells during development, termination of immune responses, and immunosurveillance
extrinsic pathway uses what caspases for initiation of apoptosis
caspases 8 and 10
extrinsic pathway is initiated by activation of
Tumor Necrosis Factor (TNF) receptor family of “cell death receptors” such as the Fas receptor
extrinsic pathway: first step
killer lymphocytes express FAS ligands on their cell surface
extrinsic pathway: how do killer lymphocytes bind to target cells
through the FAS Death receptors
extrinsic pathway: once the FAS ligand and its receptors are bound…what do they do next
they recruit adaptor molecules through binding between the receptor death domain and the adapter cell domain —>procaspases aggregate by binding to the “death effector domain” of the adaptor hence forming DISC (Death-inducing signaling complex)
extrinsic pathway: what happens after procaspases have aggregated at the death effector domain
they are cleaved to form active caspase 8 which then activate other procaspases —> lead to apoptosis
how are extrinsic and intrinsic pathways coupled
Death Receptors activate Bid which subsequently activates Bak and Bax
what pathway is activated in response to viral infected cells
perforin/granzyme pathway
perforin/granzyme pathway: what secretes perforin and granzyme
cytotoxic T cells
perforin/granzyme pathway: what does perforin do
forms pore in target cells
perforin/granzyme pathway: what does granzyme do
they enter the cells through the perforin and activate caspase 10 into resulting in inactivation of apoptotic inhibitors and activate caspase 3 to execute apoptosis
target of caspases
apoptosis regulators, cell adhesion molecules, cytoskeletal proteins, and nuclear structural proteins
what can inhibit apoptosis
binding of extracellular survival factors to cell surface receptors —> activation and production of apoptotic inhibitors such as Bcl-2 and the inactivation of proapoptotic proteins such as Bad
cells that require constant signaling to prevent apoptosis
nerve cells during development
p53 can induce apoptosis by increasing expression of
pro-apoptotic Bcl2 family members, FAS receptors (CD95), IGFBP-3
dna fragmentation in apoptotic cells facilitated by
caspase activated Dnase enzyme that cleaves at internucleosomal sites
cleavage typically occurs at ____ intervals resulting in a ladder effect when apoptotic DNA is visualized by gel electrophoresis.
180 bp
how are DNA cell fragmentation detected in cells in situ
using DNA end labeling techniques such as
TUNEL
Changes in the plasma membrane of an apoptotic cell results in the exposure of
phosphatidylserine
what type of assays can be used to detect active caspase
caspase assay
labeled antibodies for ______ can label apoptotic cells
annexin 5
cancer cells express high levels of proteins and low levels of what proteins
high level of apoptotic inhibitors Bcl2
low levels of apoptotic cells p53
common neurodegenerative disorder
Alzheimers
Alzheimer’s is characterized by the presence of
senile plaques, neurofibrillary tangles, and massive loss of neurons
genes implicated in alzheimers
amyloid precursor protein (APP)
apolipoprotein E
presenilins 1 (PS1) and 2 (PS2)
in alzheimers brain, there is increased levels of
proapoptotic Bak and Bad protein
amyloid precursor protein (APP), presenilins 1 and 2 (PS1 and PS2) are cleaved by
caspase 3 (its activity increased)
HIV infection leads to inactivation of what proteins
anti apoptotic protein Bcl2 and activation of procaspases
HIV infection promotes what pathway in CD4+ cells
extrinsic FAS mediated apoptosis
HIV proteins such as tat, nef and vpr may induce apoptosis by interacting with
p53