RNA interference and other cell-autonomous defenses IFN-induced - PowerPoint PPT Presentation

RNA interference and other cell-autonomous defenses

IFN-induced antiviral mediators / λ IFN system as well as many IFN-induced antiviral mediators are absent in plants What constitutes antiviral response in plants (nematodes and insects)? RNA interference?

RNA interference http://www.nature.com/focus/rnai/animations/

Players of today’s lecture C. elegance Drosophila Arabidopsis thaliana Vertebrates

Types of dsRNAs siRNAs miRNAs (siRNAs)

Major steps and mediators of si/miRNA pathways Insect antiviral system

Evolution of si/miRNA pathway Substrate specificity of Dicers Dicer family Arabidopsis DCL1; -2; -3; -4 miRNA siRNA (22, 21, 24 nucleotides) Drosophila Dicer-1 Dicer-2 miRNA siRNA C. elegant, vertebrates Dicer-1 miRNA; siRNA

Sources of dsRNAs Plants and worms RNA-dependent Secondary siRNAs RNA polymerases (RDRPs)

Transitivity (generation of secondary siRNAs)

Dicer Products (mature dsRNAs) monophosphate in primary siRNAs di- or triphosphates in secondary siRNAs

Dicer Products (mature dsRNAs) methylated

Executor complex - RNA-induced silencing complex (RISC) Multisubunit (multifunctional) complexes Argonaute (Ago) dsRNA-binding proteins (DRBs) Nucleases (dicers) Helicases … C. elegans – 26; Arabidopsis - 10 Drosophila (5 Ago) Ago-1 Ago-2 miRNA siRNA

Inhibition of translation

Inhibition of transcription

Role of RNA interference in antiviral response Evidence: Virus-derived (vi-siRNAs) accumulate during infections (plants) Viruses produce suppressors of RNA silencing (vSRS) siRNAs miRNAs (lsiRNAs?) Indirect antiviral effect Direct antiviral effect Inhibition of suppressors of various proteins of defense response

siRNA mediated immunization

siRNA mediated antiviral response (race for survival)

Viral evasion of RNA silencing Viruses (plant viruses) produce vSRS: sequestering dsRNAs (dsRNA-binding properties) inhibition of vi-dsRNA processing targeting 3’ methylation (stability of siRNAs is affected) competing with Ago for ssRNA binding binding Ago directly and preventing slicing targeting Ago (RISC) for degradation degradation of primary vi-dsRNAs inhibition of RDRP and generation of secondary vi-dsRNAs dsRNA spread? …

Is RNA silencing involved in antiviral response in organisms other than plants? Animal viruses: Use miRNA system for their advantage (HCV replication) Encode multiple vmiRNAs However: Encode vSRS proteins miRNAs (IFN-induced miRNAs) inhibit viral replication vi-miRNAs target cellular (or viral genes) for the inhibition

Additional reading: review by Ding & Voinnet (2007) Cell 130 , p413-426 Student assignment: read and prepare to discuss paper by Marques et al. (2006) Nat Biotech 24 , 559-556