Protein Synthesis - Viruses and Cancer

Question 1

EIF4E

Answer 1

translation - recognize cap

Question 2

EIF4G

Answer 2

translation - scaffolding cap

Question 3

EIF4A

Answer 3

translation - RNA helicase

Question 4

EIF2

Answer 4

brings GTP, 40S ribosomal subunit, ATP hydrolysis initiates start, central of regulation

Question 5

EIF2 regulation

Answer 5

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!

Question 6

HCR

Answer 6

phosphorylates EIF2

hemin control repressor - RBC hgb sensor - controls production of heme/globin

coordinate thalessemia if too high or too low

Question 7

PKR

Answer 7

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

Question 8

GCN2

Answer 8

histidine kinase

phosphorylates EIF2

cells don’t store histidine - if don’t have it - decrease synthesis

Question 9

PERK

Answer 9

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

Question 10

NS1

Answer 10

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

Question 11

adenovirus with EBV

Answer 11

makes a decoy dsRNA - blocks site in PKR so it can’t phosphorylate EIF2 and translation of viral genes can occur

Question 12

K3L

Answer 12

Pox virus!

Looks like EIF2 - PKR binds K3L instead of EIF2alpha, no EIF2 phosphorylation –> translation

cell thinks it’s phosphorylating EIF2alpha

Question 13

Internal Ribosome entry

Answer 13

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

Question 14

4EBP

Answer 14

translation repressor!

binds to 4E - when bound, there is NO translation! inhibitor - makes EIF4E unable to bind to cap

Question 15

mTOR

Answer 15

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

Question 16

Picornaviral RNA translation

Answer 16

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

Question 17

Poliovirus translational control

Answer 17

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

Question 18

HCV translation

Answer 18

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

Question 19

cellular IRESes

Answer 19

binds EIF4G and brings it in directly!

no common strucutre - multiple short modules

Question 20

VEGF

Answer 20

most important mRNA with IRES - stimulates growth

signal protein

PTC299 inhibits - blocks abilitiy of 4G to interact during hyposia

mRNA translation under stress

Question 21

PTC299

Answer 21

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)

Question 22

Nonsense mediated decay

Answer 22

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)

Question 23

DMD Drug

Answer 23

for NMD

premature stop –> stall –> ribosome inserts nearest cognate RNA - inserts tryptophan! makes full protein (no decay) but need right codon

Question 24

miRNA

Answer 24

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

Question 25

Drosha

Answer 25

processes miRNA

Question 26

Exportin5

Answer 26

exports miRNA to the cytoplasm

Question 27

dicer

Answer 27

in cytoplasm - removes more nt from miRNA