tetano
Editor, Senior Moderator
J Virol. 2015 Mar 25. pii: JVI.00232-15. [Epub ahead of print]
[h=1]Influenza A Virus Panhandle Structure is Directly Involved in RIG-I Activation and IFN Induction.[/h] Liu G[SUP]1[/SUP], Park HS[SUP]2[/SUP], Pyo HM[SUP]3[/SUP], Liu Q[SUP]4[/SUP], Zhou Y[SUP]5[/SUP].
[h=3]Author information[/h]
[h=3]Abstract[/h] Retinoic acid-inducible gene I (RIG-I) is an important innate immune sensor that recognizes viral RNA in the cytoplasm. Its non-self recognition largely depends on the unique RNA structures imposed by viral RNA. The panhandle structure residing in the influenza A virus (IAV) genome, whose primary function is to serve as the viral promoter for transcription and replication, has been proposed to be a RIG-I agonist. However, it has never been proved experimentally. Here, we employed multiple approaches to determine if the IAV panhandle structure is directly involved in RIG-I activation and type I interferon (IFN) induction. First, in porcine alveolar macrophages, we demonstrated that viral genomic coding region is dispensable for RIG-I-dependent IFN induction. Second, using in vitro synthesized hairpin RNA, we showed that the IAV panhandle structure could directly bind to RIG-I and stimulate IFN production. Furthermore, we investigated the contribution of the wobble base pairs, mismatch, and unpaired nucleotide within the wild-type panhandle structure to RIG-I activation. Elimination of these destabilizing elements within the panhandle structure promoted RIG-I activation and IFN induction. Given the function of the panhandle structure as the viral promoter, we further monitored the promoter activity of these panhandle variants and found that the viral replication was moderately affected whereas the viral transcription was impaired dramatically. In all, our results indicate that the IAV panhandle promoter region adopts a nucleotide composition that is optimal for balanced viral RNA synthesis and suboptimal for RIG-I activation.
[h=4]IMPORTANCE:[/h] The IAV genomic panhandle structure has been proposed to be the RIG-I agonist due to its partial complementarity; however, it has not been experimentally confirmed. Here, we provided direct evidence that the IAV panhandle structure is competent in, and sufficient for RIG-I activation and IFN induction. By constructing panhandle variants with increased complementarity, we demonstrated that wild-type panhandle structure could be modified to enhance RIG-I activation and IFN induction. These panhandle variants posed moderate influence on viral replication but dramatic impairment on viral transcription. These results indicate that the IAV panhandle promoter region adopts a nucleotide composition to achieve optimal balance of viral RNA synthesis and suboptimal RIG-I activation. Our results highlight the multifunctional role of the IAV panhandle promoter region in the virus life cycle, and offer novel insights into the development of antiviral agents aiming to boost RIG-I signaling or virus attenuation by manipulating this conserved region.
Copyright ? 2015, American Society for Microbiology. All Rights Reserved.
PMID: 25810557 [PubMed - as supplied by publisher]
[h=1]Influenza A Virus Panhandle Structure is Directly Involved in RIG-I Activation and IFN Induction.[/h] Liu G[SUP]1[/SUP], Park HS[SUP]2[/SUP], Pyo HM[SUP]3[/SUP], Liu Q[SUP]4[/SUP], Zhou Y[SUP]5[/SUP].
[h=3]Author information[/h]
[h=3]Abstract[/h] Retinoic acid-inducible gene I (RIG-I) is an important innate immune sensor that recognizes viral RNA in the cytoplasm. Its non-self recognition largely depends on the unique RNA structures imposed by viral RNA. The panhandle structure residing in the influenza A virus (IAV) genome, whose primary function is to serve as the viral promoter for transcription and replication, has been proposed to be a RIG-I agonist. However, it has never been proved experimentally. Here, we employed multiple approaches to determine if the IAV panhandle structure is directly involved in RIG-I activation and type I interferon (IFN) induction. First, in porcine alveolar macrophages, we demonstrated that viral genomic coding region is dispensable for RIG-I-dependent IFN induction. Second, using in vitro synthesized hairpin RNA, we showed that the IAV panhandle structure could directly bind to RIG-I and stimulate IFN production. Furthermore, we investigated the contribution of the wobble base pairs, mismatch, and unpaired nucleotide within the wild-type panhandle structure to RIG-I activation. Elimination of these destabilizing elements within the panhandle structure promoted RIG-I activation and IFN induction. Given the function of the panhandle structure as the viral promoter, we further monitored the promoter activity of these panhandle variants and found that the viral replication was moderately affected whereas the viral transcription was impaired dramatically. In all, our results indicate that the IAV panhandle promoter region adopts a nucleotide composition that is optimal for balanced viral RNA synthesis and suboptimal for RIG-I activation.
[h=4]IMPORTANCE:[/h] The IAV genomic panhandle structure has been proposed to be the RIG-I agonist due to its partial complementarity; however, it has not been experimentally confirmed. Here, we provided direct evidence that the IAV panhandle structure is competent in, and sufficient for RIG-I activation and IFN induction. By constructing panhandle variants with increased complementarity, we demonstrated that wild-type panhandle structure could be modified to enhance RIG-I activation and IFN induction. These panhandle variants posed moderate influence on viral replication but dramatic impairment on viral transcription. These results indicate that the IAV panhandle promoter region adopts a nucleotide composition to achieve optimal balance of viral RNA synthesis and suboptimal RIG-I activation. Our results highlight the multifunctional role of the IAV panhandle promoter region in the virus life cycle, and offer novel insights into the development of antiviral agents aiming to boost RIG-I signaling or virus attenuation by manipulating this conserved region.
Copyright ? 2015, American Society for Microbiology. All Rights Reserved.
PMID: 25810557 [PubMed - as supplied by publisher]