Transcript 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!