Small interfering RNA pathway contributes to antiviral immunity in Spodoptera frugiperda (Sf9) cells following Autographa californica multiple nucleopolyhedrovirus infection

• Published in: Insect biochemistry and molecular biology Vol. 101; pp. 24 - 31
• Main Authors: Karamipour, Naeime, Fathipour, Yaghoub, Talebi, Ali Asghar, Asgari, Sassan, Mehrabadi, Mohammad
• Format: Journal Article
• Language: English
• Published: England Elsevier Ltd 01-10-2018
• Subjects: Animals; Antiviral defense; Argonaute Proteins - antagonists & inhibitors; Argonaute Proteins - genetics; Argonaute Proteins - immunology; Gene Expression Regulation; Genome, Viral; Host-Pathogen Interactions; Host-virus interactions; Insect Proteins - antagonists & inhibitors; Insect Proteins - genetics; Insect Proteins - immunology; Nucleopolyhedrovirus - genetics; Nucleopolyhedrovirus - growth & development; Nucleopolyhedrovirus - metabolism; Ribonuclease III - antagonists & inhibitors; Ribonuclease III - genetics; Ribonuclease III - immunology; RNA, Messenger - antagonists & inhibitors; RNA, Messenger - genetics; RNA, Messenger - immunology; RNA, Small Interfering - genetics; RNA, Small Interfering - immunology; Sf9 Cells; Signal Transduction; siRNA; Small RNAs; Spodoptera - genetics; Spodoptera - immunology; Spodoptera - metabolism; Spodoptera - virology; Viral Proteins - genetics; Viral Proteins - metabolism; Virus Replication; Antiviral defense; siRNA; Host-virus interactions; Small RNAs
• ISSN: 0965-1748; 1879-0240
• DOI: 10.1016/j.ibmb.2018.07.004

Autographa californica multiple nucleopolyhedrovirus (AcMNPV) is a well-known virus in the Baculoviridae family. Presence of the p35 gene in the AcMNPV genome as a suppressor of the short interfering RNA (siRNA) pathway is a strong reason for the importance of the siRNA pathway in the host cellular defense. Given that, here we explored the roles of Dicer-2 (Dcr2) and Argonaute 2 (Ago2) genes, key factors in the siRNA pathway in response to AcMNPV infection in Spodoptera frugiperda Sf9 cells. The results showed that the transcript levels of Dcr2 and Ago2 increased in response to AcMNPV infection particularly over 16 h post infection suggesting induction of the siRNA pathway. Reductions in the expression levels of Dcr2 and Ago2 by using specific dsRNAs in Sf9 cells modestly enhanced production of viral genomic DNA which indicated their role in the host antiviral defense. Using deep sequencing, our previous study showed a large number of small reads (siRNAs of ∼20 nucleotides) from AcMNPV-infected Sf9 cells that were mapped to some of the viral genes (hot spots). Down-regulation of Dcr2 in Sf9 cells resulted in enhanced expression levels of the selected virus hotspot genes (i.e. ORF-9 and ORF-148), while the transcript levels of virus cold spots (i.e. ORF-18 and ORF-25) with no or few siRNAs mapped to them did not change. Overexpression of AcMNPV p35 as a suppressor of RNAi and anti-apoptosis gene in Sf9 cells increased virus replication. Also, replication of mutant AcMNPV lacking the p35 gene was significantly increased in Sf9 cells with reduced transcript levels of Dcr2 and Ago2, highlighting the antiviral role of the siRNA pathway in Sf9 cells. Together, our results demonstrate that Dcr2 and Ago2 genes contribute in efficient antiviral response of Sf9 cells towards AcMNPV, and in turn, the AcMNPV p35 suppresses the siRNA pathway, besides being an antiapoptotic protein.
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•Small interfering RNA pathway (siRNA) induced in response to AcMNPV infection.•Dcr2 and Ago2 genes have antiviral roles in Sf9 cells.•The presence of the p35 gene of AcMNPV enhanced the viral replication through suppression of siRNA pathway.•SiRNA pathway targets the viral transcript thereby attenuating virus replication.