title: Arginine rich short linear motif of HIV-1 regulatory proteins inhibits dicer dependent RNA interference.
abstract: BACKGROUND
  Arginine Rich Motif (ARM) of HIV-1 Tat and Rev are extensively studied linear motifs (LMs). They are already established as an inefficient bipartite nuclear localisation signal (NLS). The unusual passive diffusion of HIV-1 NLS tagged reporter proteins across the nucleus is due to an unknown competing functionality of ARM. Recent findings about the role of retroviral proteins as a suppressor of RNA interference (RNAi) involving their basic residues hint an interesting answer to this alternate functionality. The present work explores the role of HIV-1 ARM as a uniquely evolved viral motif to combat Dicer dependent RNAi.
  
  
  RESULTS
  We show that RNA binding ARM of both HIV-1 Tat and Rev is a LM with a pattern RXXRRXRRR unique to viruses. Extending the in silico results to wet lab, we proved both HIV-1 Tat and Rev can suppress Dicer dependent RNA silencing process involving ARM. We show, HIV-1 Tat and Rev and their corresponding ARM can bind the RISC loading complex (RLC) components TRBP and PACT confirming ARM as an independent RNAi suppression motif. Enhancement of RNAi in infection scenario through enoxacin increases HIV-1 replication as indicated by p24 levels. Except Dicer, all other cytoplasmic RNAi components enhance HIV-1 replication, indicating crucial role of Dicer independent (Ago2 dependent) RNAi pathway in HIV-1 infection. Sequence and structural analysis of endo/exo-microRNA precursors known to be regulated in HIV-1 infection highlights differential features of microRNA biogenesis. One such set of miRNA is viral TAR encoded HIV-1-miR-TAR-5p (Tar1) and HIV-1-miR-TAR-3p (Tar2) that are known to be present throughout the HIV-1 life cycle. Our qPCR results showed that enoxacin increases Tar2 miRNA level which is interesting as Tar2 precursor shows Ago2 dependent processing features.
  
  
  CONCLUSIONS
  We establish HIV-1 ARM as a novel viral motif evolved to target the Dicer dependent RNAi pathway. The conservation of such motif in other viral proteins possibly explains the potent suppression of Dicer dependent RNAi. Our model argues that HIV-1 suppress the processing of siRNAs through inhibition of Dicer while at the same time manipulates the RNAi machinery to process miRNA involved in HIV-1 replication from Dicer independent pathways.
authors.affiliation: Virology Lab II, National Institute of Immunology, Aruna Asaf Ali Marg, New Delhi, 110067, India. sanket@nii.res.in.
authors.forename: Sanket Singh
authors.initials: SS
authors.lastname: Ponia
authors.forename: Sakshi
authors.initials: S
authors.lastname: Arora
authors.forename: Binod
authors.initials: B
authors.lastname: Kumar
authors.forename: Akhil C
authors.initials: AC
authors.lastname: Banerjea
mesh_terms: D053487:DEAD-box RNA Helicases / Q000037:antagonists & inhibitors*; D015497:HIV-1 / Q000502:physiology*; D054884:Host-Pathogen Interactions; D006801:Humans; D034622:RNA Interference; D043244:Ribonuclease III / Q000037:antagonists & inhibitors*; D054321:rev Gene Products, Human Immunodeficiency Virus / Q000378:metabolism*; D054322:tat Gene Products, Human Immunodeficiency Virus / Q000378:metabolism*
chemical_list: D054321:rev Gene Products, Human Immunodeficiency Virus; C514860:rev protein, Human Immunodeficiency Virus-1; D054322:tat Gene Products, Human Immunodeficiency Virus; C408087:DICER1 protein, human; D043244:Ribonuclease III; D053487:DEAD-box RNA Helicases
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