Download P-bodies

Lucie Bartoníčková
ZIB seminar 27th October, 2008
eukaryotic mRNA – subcellular localizations:
polysomes - translating mRNA
stress granules
- mRNA stopped in translation initiation
P-bodies – mRNA for degradation + translation repression
(= „a place to die, a place to sleep“)
mRNP granules (byproducts of mRNA metabolism)
(P granules)
S.cerevisiae
(yeast,mammals)
human cell culture
(also Drosophila, amphibians)
(mammals)
C.elegans - germ cells
rat hippocampal neurons
chicken fibroblast
(mammal neurons)
(Wickens, Science 2003)
interaction with viral life cycles
P-bodies
stress granules
accumulation of some viral RNAs/proteins
Are P-bodies and SGs important for viral life cycles?
Or for limiting viral infection?
How RNA viruses segregate replication & assembly from translation?
CYCLING OF EUKARYOTIC mRNA
stress granule
polysomes
(Parker&Sheth, MolCell 2007)
P-body
P-BODIES
(processing bodies)
cytoplasmic foci: aggregates of translationally repressed mRNPs
translation repression & mRNA degradation
gene silencing
conserved core proteins:
• mRNA decapping machinery
• deadenylase complex
general repression / decay machinery
additional proteins:
species/condition specific: • mi/siRNA repression factors (RISC)
• RNA binding prot-s + translation repressors
• nonsense-mediated decay (NMD) proteins
= degradation of improperly processed mRNA
(premature stop-codons)
proteins affecting viral function - e.g. antiviral APOBEC deaminase
DEGRADATION OF EUKARYOTIC mRNA
deadenylation-dependent pathways
Ccr4p/Pop2p(Caf1)/Not cx
major cytoplasmic
deadenylase
1) deadenylation
P-bodies
2a)
2b)
5´→ 3´exonuclease
proteins involved
in decapping
Ski cx
(= cx of 3´→ 5´
exonucleases)
decapping cx
3´→5´ degradation
decapping + 5´→ 3´ decay
predominant in yeast
predominant in mammals
(adapted from Parker&Sheth, MolCell 2007)
GENE SILENCING
miRNAs
(= microRNAs)
siRNAs
(= short interfering RNAs)
= dsRNase
~ 21- 23 nt
RNA-induced silencing
complex
RNA interference
3ˇuntranslated region
of target mRNA
translation repression
destruction of target RNA
(Lodish et al.,5th ed., adapted from Hutvágner& Zamore 2002)
GENE SILENCING & P-bodies
miRNAs
siRNAs
may target mRNAs into P-bodies
mRNA decay
*
*
*
*
*
*
translation repression
mRNA decay (mainly in plants)
* = P-body components
AGO*= Argonaute proteins – essential components of RISC
characterictic domains: PAZ & PIWI (similar to RNase-H domain)
(Eulalio, Nat Rev Mol Cell Biol 2007)
STRESS GRANULES
transient cytoplasmic bodies induced upon environmental stress
(response to defects in translation initiation)
contain aggregates of mRNA + translation initiation factors
48S preinitiation cx: eIF4 subunits, 40S ribosomal
subunits, poly(A)binding protein 1 (PABP-1)
RNA binding proteins with self-interaction domains
(TIA proteins)
often associated with P-bodies
? mRNA moving between the compartments
P-bodies & VIRUSES
effects of mutations in various core P body components on viral life cycles
group
retrotransposons
+RNA
viruses
retroviruses
virus
studied
virus-like element
in
Ty1 & Ty3
yeast
reduced retrotransposition
Ty3
yeast
enhanced retrotransposition
brome mosaic virus
yeast
reduced translation & rectruitment
to replication
HCV
mammalian
cell culture
reduced replication
HIV
mammalian
cell culture
reduced nuclear export and
translation of unspliced HIV-1
transcripts
phenotype of mutations
a) retrotransposons and P-bodies
retrotransposons
form virus like particles
model: yeast Ty1 (copia-like family) & Ty3 (gypsy-like)
may require P-bodies for life cycle:
Δs in several prot-s
promoting P-body
formation
reduced retrotransposition,
→ altered subcellular distribution
of Ty3 proteins
pop2Δ (deadenylase cx) → enhanced retrotransposition
? role in assembly/maturation of Ty VLPs
tagged Ty3 RNA & proteins accumulate in P-bodies
(Roth, Yeast 2000)
Ty element life cycle
precise function still unclear
b) retroviruses and P-bodies
HIV
cellular proteins:
Crm1p & RNA helicase DDX3 - required for nuclear export of unspliced HIV-1 RNA
→ possible recruitment of HIV-1 genomic RNA to P-bodies for packaging?
(Crm1p required for export of P-body components)
other retroviruses
localisation of viral components (Gag, Pol) to discrete cytoplasmic foci
= ?? P-bodies
c) + RNA viruses
brome mosaic virus
(studied in yeast – complete viral life cycle)
tripartite genome: RNA1, RNA2, RNA3 – capped, lack poly(A)
1) P-body components (generally translation repressors) required for RNA1-3 translation
WHY?
2) P-body components required for RNA1-3 replication (membrane-bound complex)
- concentrating genomic RNAs+proteins
- promoting interaction with membranes
HCV
HCV core protein colocalizes in cytoplasm foci (? P-bodies)
HCV replication enhanced by interaction with liver-specific miRNA
? P-body components important for efficient HCV replication ?
P-bodies & stress granules in ANTIVIRAL DEFENCE
miRNAs
siRNAs
may recruit P-body components to target mRNAs
→ translation repression + mRNA degradation
antiviral APOBEC proteins - accumulate in P-bodies & SGs (during stress)
(apolipoprotein B mRNA-editing enzyme)
= cytidine deaminases
(x retroviruses, retrotransposons)
x (HIV-1 Vif protein → APOBEC3G degradation)
transient SGs formation triggered by some viral infections
SGs may limit viral infections (e.g. VSV ((-)RNA), Sindbis v.(+RNA), HSV (DNA), polio)
x some viruses interfere with SGs formation
Host defence or host defeat?
P-bodies & stress granules – positive x negative influence on viral life cycles
host defence:
repressing function of viral transcripts
promoting viral life cycle:
• viral transcription
• nuclear-cytoplasmic transport + remodeling of viral RNPs
• concentration of mRNAs - ? recruitment of viral mRNAs
for translation, replication, assembly
Thank you for your attention!