Cell Proliferation/apoptosis Flashcards
describe how cell proliferation occurs?
- growth factors bind to their cytokine receptors
e.g. EGF/ PDGF - activated intracellular signalling
- change in gene transcription
e.g. up/down-regulation of gene transcription - knock-on effects on DNA replication, cell cycle, mitosis etc.
how can cell proliferation drive cancer progression?
down-regulation of cytokine signalling to initiate/stop gene transcription
what are proto-oncogenes?
normal genes that control proliferation/growth that can become oncogenes due to mutations/increased expression
what are some examples of oncogenes/tumour-inducing agents?
- Gene amplification/over expression: HER2 in breast cancer
- Translocations resulting in hybrid oncogene: BCR-ABL in leukemia
- Missense mutations resulting in constitutively active protein: EGFR in lung cancer, B- RAF in melanoma
describe tumour cells compared to normal cells, in terms of genes.
increase no. of proto-oncogenes
increase gene transcribed
increase gene expression
what receptors do growth factors bind to?
mainly tyrosine kinase receptors
Tyr R
describe Tyr R ?
dimer receptor
what happens when growth factors bind to the Tyr R ?
becomes phosphorylated
causes…
- conformational change
- dimerisation
- activation of tyrosine kinase activity
how can additional receptors bind to Tyr R?
Tyr R is activated and phosphorylated
phosphorylated residues allow various cytoplasmic receptors to join
what are some examples of Tyr R?
PGDF receptor
EGF receptor
Insulin
IGF receptor (insulin-like GF)
what are some examples of growth factors?
platelet-derived growth factors
epidermal growth factors
insulin
insulin-like growth factors
transforming growth factors (TGF-a and TGF-b)
what are some examples of receptors that bind to Tyr R?
RAS pathway
serine/threonine kinase cascades
P.I./lipid signalling pathway
other tyrosine kinases
phospholipase Cy
which receptors that bind to Tyr R drive gene proliferation?
RAS pathway
serine/threonine kinase cascades
other tyrosine kinases
what happens to Tyr R in cancerous tumour?
- amino acid changes/partial deletion
= change tyr activity
= loss of ‘receptor domain’
= GF independent signalling - gene amplification/over-expression
- increased expression of normal receptors
- overexpression of aberrant receptors
what is HER2?
an epidermal growth factor receptor (EGFR)
amplifaction/duplication of HER2 gene in breast cancer
what is BCR-ABL?
a fusion kinase = BCR- ABL increases cell proliferation
- BCR = promotes cell survival
- tyr kinase
- GTP regulator - ABL = promotes cell survival
- cytoplasmic Tyr Kinase
what happens when BCR and ABL genes fuse?
BCR loses GTP regulation
ABL loses inhibitory domain which inactivates ABL
= INCREASES BLOOD CELL PROLIFERATION = leukemia
what genes are apart of the RAS family?
h-ras
k-ras
n-ras
why is the RAS family important?
Most commonly mutated oncogene
what is a common oncogenic mutation in the RAS cycle?
reduced GTPase-activating proteins = no inactivation of RAS = increased cell proliferation due to constant RAS signalling
what does activated RAS do?
phosphorylated MEK which phosphorylates ERK = phosphorylates to activated transcription factors
where is B-RAF mutations common?
melanoma (80%)
lung
colorectal cancers
where do B-RAF mutations occur?
RAS cycle
what is cell apoptosis?
programmed cell death,
allows elimination of damaged cells
what mediates cell apoptosis? and how?
caspases (caspase-9 into caspase-7 & caspase-3) by cleaving cellular proteins and indirectly cellular DNA
describe cell apoptosis method
- Condensation of nuclei and fragmentation of chromosomal DNA
- Condensation and fragmentation of cytoplasm
- Release of mitochondrial cytochrome C
- Membrane blebbing
- Phagocytic clearance
how is apoptosis controlled?
in healthy cells - BCL2 represses apoptosis
apoptotic stimuli inhibit BCL2
what are apoptotic stimuli?
pro-apoptotic receptor
cellular stress (DNA damage, loss of growth factors, anoxia, infection and oxidative stress)
what is p53?
transcriptional factor responds to DNA damage
1. promotes apoptosis if damages are not reparable via activation of pro-apoptotic genes
2. suppresses anti-apoptotic factors
what are the 4 main outcomes of an activated p53?
- angiogenesis
- growth arrest
- DNA repair
- apoptosis
what are some treatments relating p53?
chemotherapy that induces larger levels of DNA damage to induce p53- dependent apoptosis
whats MDM2?
negative regulator of p53
degrades p53
negative feedback
what happens if MDM2 is overexpressed?
loss of p53 activity due to larger degradation
where is cytochrome C released from?
mitochondria via BAX/BAK pro-apoptotic genes
what do caspase 3 and caspase 6 do?
DNA fragmentation and protein cleavage
why is cytochrome c released ?
detects levels of intrinsic stress
what does BCL-2 do?
repress cellular apoptosis by suppressing BAX/BAK = inhibit cytochrome C release
what is the expression of BCL-2 in cancerous cells?
over expressed
How do we target treatments to control proliferation/cell death?
- target RTKs
- target BCL-2/BCL-XL
how do we targets RTK?
- target antibodies to receptor
- inhibit ligand binding
- inhibit dimerisation
- induce cell killing of tumour cells
- inhibit phosphorylation - small molecules inhibit RTK (intracellulary)
what antibodies target RTKs?
- trastuzumab (HERCEPTIN)
- blocks internalisation
- partial block of downstream signalling
- promotes antibody-dependent cytotoxicity = kills tumour cells - pertuzumab
- blocks dimerisation and activation
- effective when HER2 is activated not overexpressed - cetuxumab
- blocks EGF binding - panitumumab
- blocks EGF binding
what are HER2 targeted treatment?
trastuzumab - mAb
pertuzumab - mAb
lapatinib - small molecule
for breast cancer
what are EGFR targeted treatment?
cetuximab - colorectal cancer
panitumumab - colorectal cancer
erlotinib - lung cancer
what is erlotinib?
reversible ATP competitor (small molecules) IN EGFR inihibitor
resistance can occur EGFR
what are BCR-ABL inhibitors?
IMATINIB drug - some ppl experience resistance and relapse
used in CML - Chronic myelogenous leukemia
MOA of BCR-ABL inhibitors?
competitively inhibit of ATP binding to active site = inhibit TYR K
