Protein Synthesis - Viruses and Cancer Flashcards
EIF4E
translation - recognize cap
EIF4G
translation - scaffolding cap
EIF4A
translation - RNA helicase
EIF2
brings GTP, 40S ribosomal subunit, ATP hydrolysis initiates start, central of regulation
EIF2 regulation
EIF2B = Ras Rho ATPase - controls synthesis, makes GTP –> GDP EIF2 phosphorylated at alpha subunit in response to stress, if it is phosphorylated, it has 100x affinity for EIF2B –> sequester EIF2B, can’t hydrolyze GTP, translation stops! 1/10 as much EIF2B as EIF2, even if just 10% increase in EIF2 phosphorylation blocks synthesis - very small changes!
HCR
phosphorylates EIF2
hemin control repressor - RBC hgb sensor - controls production of heme/globin
coordinate thalessemia if too high or too low
PKR
dsRNA activated kinase - phosphorylates EIF2
viral infection senesor - major action of IFNs
dsRNA is an alarm that a virus is present! we don’t make dsRNA but viruses do
ssRNA - to replicate need dsRNA
GCN2
histidine kinase
phosphorylates EIF2
cells don’t store histidine - if don’t have it - decrease synthesis
PERK
ER stress kinase
phosphorylates EIF2
cells rapidly glycosylated in ER
necrotic of more rapid than ER can accomodate - shut down protein synthesis to catch up
NS1
pathogenic flu makes to evade PKR
NS1 binds dsRNA and masks it so PKR can’t see it, blocks activation of PKR
allows viral gene transcription to occur
adenovirus with EBV
makes a decoy dsRNA - blocks site in PKR so it can’t phosphorylate EIF2 and translation of viral genes can occur
K3L
Pox virus!
Looks like EIF2 - PKR binds K3L instead of EIF2alpha, no EIF2 phosphorylation –> translation
cell thinks it’s phosphorylating EIF2alpha
Internal Ribosome entry
viral mechanism to bypass/avoid inhibition by antiviral responses
when cells are infected –> inactivate cap binding proteins so can’t initiate translation from the cap
viruses are derived from cell mechansism used during stress response to translate certain proteins (wound healing)
this is exploited
4EBP
translation repressor!
binds to 4E - when bound, there is NO translation! inhibitor - makes EIF4E unable to bind to cap
mTOR
protein kinase - phosphorylated EIF4EBP
when EIF4EBP is phosphorylated - it can’t bind to EIF4E - translation occurs!
if growth signals, mTOR is activated –> phosphorylated EIF4EBP –> 4E binds to cap and translation
if tumor growing things (heat shock, hypoxia, infection) –> mTOR is turned OFF –> can’t phosphorylated 4EBP –> binds to 4E –> no translation can occur
Picornaviral RNA translation
no cap!
long 5’ UTR on mRNA
multiple possible translation start sites
single huge polypeptide - replication proteins all on one end
no EIF4E needed - can be transcribed even if 4E isn’t there
Poliovirus translational control
makes 2A and 2C in polypeptide - splice selves out and process polypeptide - splice out rest
2A - has one active site that acts as a translation factor for EIF2E
cleaves 1/3 of EIF4G - the part that binds to 4E!
leaves rest of translation on machinery on 4G but cuts out part that needs to recognize cap
HCV translation
IRES
structural hook - latches ribosome and brings juxtaposition of initiation site
mechanism to avoid dependence on cap for translation - way to bypas 4E but get the rest of the mechanism
cellular IRESes
binds EIF4G and brings it in directly!
no common strucutre - multiple short modules
VEGF
most important mRNA with IRES - stimulates growth
signal protein
PTC299 inhibits - blocks abilitiy of 4G to interact during hyposia
mRNA translation under stress
PTC299
blocks VEGF noncoding/IRES region
used primarily in tumor VEGF mRNA translation!
now antibody mediated - shut off ability for would healing
can drug under hypoxia without cap - drugs will only stop in tumor NOT normal response
in breast ca -IRES only used during hypoxia (stress)
Nonsense mediated decay
premature stop codon
recessive - truncated protein not made and can’t interfere w function of wt protein
dominant - inhibiting response that kills cells - partial protein builds up and kills cells
normal stop almost always in last codon of exon
EJC - exon junction complex - part of mRNA splicing! deposited 20-24 nt upstream of exon exon border
first translation - ribosome removes exon junction proteins bound to mRNA after splicing
EJC sits right by premature stop - EJC is still there! stall
when ribosome idles - really slow (usually instantaneous) - mRNA recruits decay machinery
if see a stop+EJC - that means its a fake stop (real stop wouldn’t still have ejc there to splice)
DMD Drug
for NMD
premature stop –> stall –> ribosome inserts nearest cognate RNA - inserts tryptophan! makes full protein (no decay) but need right codon
miRNA
small noncoding RNA
regulate eukaryotic gene expression at translation/mRNA stability levels
non coding
hiarpin
hybridize to several sites in 3’ UTR
neg regulation of gene expression
if miRNA binds perfectly - degrade mRNA! no expression
if mi has 1+ mismatch - bring and inhibit translation, deadenylation
Drosha
processes miRNA
Exportin5
exports miRNA to the cytoplasm
dicer
in cytoplasm - removes more nt from miRNA
