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Paper presenta*on by Janique Bertschi
20.05.2014
1 IRES = internal ribosome entry site, eIF4A = eukaryo*c ini*a*on factor-‐4A
What is the paper about?
2
What is the paper really about?
INR = insulin-‐like receptor 3
= insulin
?
cap-‐binding complex forma*on
mRNA transla*on
The alterna*ve way of transla*on ini*a*on: IRES
IRES = internal ribosome entry site 4
• well known from viral mRNAs • cap-‐independent
Their Hypothesis:
INR = insulin-‐like receptor , IRES = internal ribosome entry site 5
?
mRNA of e.g. INR:
5‘ UTR 3‘ UTR AAA
IRES
Experiments
6
Does Foxo ac*vate PDCD-‐4 in Drosophila cells ?
7 INR = insulin-‐like receptor , IRES = internal ribosome entry site
?
mRNA of e.g. INR:
5‘ UTR 3‘ UTR AAA
IRES
• Western blot:
• Same on mRNA level
8
Does Foxo ac*vate PDCD-‐4 in Drosophila cells ?
Drosophila cell line with inducible con-‐ stu*vely ac*ve FOXO.
YES, PDCD-‐4 is ac*vated by FOXO in Drosophila cells.
9 INR = insulin-‐like receptor , IRES = internal ribosome entry site
?
mRNA of e.g. INR:
5‘ UTR 3‘ UTR AAA
IRES
How can dINR mRNA be translated if FOXO is ac*ve?
10 INR = insulin-‐like receptor , IRES = internal ribosome entry site
mRNA of INR: 5‘ UTR 3‘ UTR
AAA
cap-‐binding complex forma*on
mRNA transla*on
How can dINR mRNA be translated if FOXO is ac*ve?
• Constructs that were cloned into Drosophila S2 cells expressing a constu,vely ac,ve form of FOXO.
Ø Dicistronic mRNAs : A high Firefly/Renilla ac*vity ra*o indicates IRES ac*vity
Ren = Renilla, FF = Firefly, IRES = internal ribosome entry site 11
cap 5‘ UTR of dINR
How can dINR mRNA be translated if FOXO is ac*ve?
dINR = drosophila insulin-‐like receptor, HCV = Hepa**s C Virus, IRES = internal ribosome entry site 12
Ø IRES ac*vity in the 5‘ UTR of dINR mRNAs mediates resistance to FOXO induces transla*on inhibi*on, comparable to the well-‐characterized IRES from Hepa,ts C Virus.
Summary
INR = insulin-‐like receptor , IRES = internal ribosome entry site 13
mRNA of e.g. INR:
5‘ UTR 3‘ UTR AAA
IRES
Actually, resistance to low levels of eIF4A was tested in more detail in the paper.
What else?
• It was also tested in a mice system if transla*on of their mINR and mIGFR mRNAs is cap-‐independent or requires eIF4A.
Ø Evolu*onary conserved mechanism J Ø Take home: Transla*on of the insulin receptor is con*nued under condi*ons of generally inhibited protein synthesis.
mINR = mouse insulin receptor, mIGFR = mouse insulin-‐like growth factor receptor-‐I
14
Outlook
Interes*ng point: As there are other geneproducts induces by FOXO, they might also have found mechanisms to escape 4E-‐BP and Pdcd4 inhibi*on.
15
16
Thanks!
Supplementary slides
17
inhibits eIF4A
Is dINR s*ll translated (via IRES) if eIF4A is directly inhibited with a small molecule called Hippuristanol?
Ø YES, dINR transla*on is specifically resistant to eIF4A inhibi*on