Influenza A viral nucleoprotein interacts with cytoskeleton scaffolding protein α‐actinin‐4 for viral replication

Sharma, Shipra; Mayank, Adarsh K.; Nailwal, Himani; Tripathi, Shashank; Patel, Jenish R.; Bowzard, John B.; Gaur, Pratibha; Donis, Ruben O.; Katz, Jacqueline M.; Cox, Nancy J.; Lal, Renu B.; Farooqi, Humaira; Sambhara, Suryaprakash; Lal, Sunil K.

Influenza A virus (IAV), similar to other viruses, exploits the machinery of human host cells for its survival and replication. We identified α‐actinin‐4, a host cytoskeletal protein, as an interacting partner of IAV nucleoprotein (NP). We confirmed this interaction using co‐immunoprecipitation studies, first in a coupled in vitro transcription‐translation assay and then in cells either transiently co‐expressing the two proteins or infected with whole IAV. Importantly, the NP–actinin‐4 interaction was observed in several IAV subtypes, including the 2009 H1N1 pandemic virus. Moreover, immunofluorescence studies revealed that both NP and actinin‐4 co‐localized largely around the nucleus and also in the cytoplasmic region of virus‐infected A549 cells. Silencing of actinin‐4 expression resulted in not only a significant decrease in NP, M2 and NS1 viral protein expression, but also a reduction of both NP mRNA and viral RNA levels, as well as viral titers, 24 h post‐infection with IAV, suggesting that actinin‐4 was critical for viral replication. Furthermore, actinin‐4 depletion reduced the amount of NP localized in the nucleus. Treatment of infected cells with wortmannin, a known inhibitor of actinin‐4, led to a decrease in NP mRNA levels and also caused the nuclear retention of NP, further strengthening our previous observations. Taken together, the results of the present study indicate that actinin‐4, a novel interacting partner of IAV NP, plays a crucial role in viral replication and this interaction may participate in nuclear localization of NP and/or viral ribonucleoproteins. STRUCTURED DIGITAL ABSTRACT: •http://www.uniprot.org/uniprot/P03466 http://www.ebi.ac.uk/ontology-lookup/?termId=MI:0915 with http://www.uniprot.org/uniprot/O43707 by http://www.ebi.ac.uk/ontology-lookup/?termId=MI:0006 (http://www.ebi.ac.uk/intact/interaction/EBI-9512541, http://www.ebi.ac.uk/intact/interaction/EBI-9512553)•http://www.uniprot.org/uniprot/Q8JR21 and http://www.uniprot.org/uniprot/O43707 http://www.ebi.ac.uk/ontology-lookup/?termId=MI:0403 by http://www.ebi.ac.uk/ontology-lookup/?termId=MI:0416 (http://www.ebi.ac.uk/intact/interaction/EBI-9514040)•http://www.uniprot.org/uniprot/Q91U50 http://www.ebi.ac.uk/ontology-lookup/?termId=MI:0915 with http://www.uniprot.org/uniprot/O43707 by http://www.ebi.ac.uk/ontology-lookup/?termId=MI:0006 (http://www.ebi.ac.uk/intact/interaction/EBI-9514006)•http://www.uniprot.org/uniprot/Q5L4H4 http://www.ebi.ac.uk/ontology-lookup/?termId=MI:0407 to http://www.uniprot.org/uniprot/O43707 by http://www.ebi.ac.uk/ontology-lookup/?termId=MI:0007 (http://www.ebi.ac.uk/intact/interaction/EBI-9512166, http://www.ebi.ac.uk/intact/interaction/EBI-9512219)•http://www.uniprot.org/uniprot/C3W6D7 http://www.ebi.ac.uk/ontology-lookup/?termId=MI:0915 with http://www.uniprot.org/uniprot/O43707 by http://www.ebi.ac.uk/ontology-lookup/?termId=MI:0006 (http://www.ebi.ac.uk/intact/interaction/EBI-9513951)•http://www.uniprot.org/uniprot/Q5L4H4 http://www.ebi.ac.uk/ontology-lookup/?termId=MI:0915 with http://www.uniprot.org/uniprot/O43707 by http://www.ebi.ac.uk/ontology-lookup/?termId=MI:0007 (http://www.ebi.ac.uk/intact/interaction/EBI-9512237)•http://www.uniprot.org/uniprot/Q6DPG0 http://www.ebi.ac.uk/ontology-lookup/?termId=MI:0915 with http://www.uniprot.org/uniprot/O43707 by http://www.ebi.ac.uk/ontology-lookup/?termId=MI:0006 (http://www.ebi.ac.uk/intact/interaction/EBI-9513984) •http://www.uniprot.org/uniprot/B2BU63 http://www.ebi.ac.uk/ontology-lookup/?termId=MI:0915 with http://www.uniprot.org/uniprot/O43707 by http://www.ebi.ac.uk/ontology-lookup/?termId=MI:0006 (http://www.ebi.ac.uk/intact/interaction/EBI-9513930) •http://www.uniprot.org/uniprot/Q5L4H4 http://www.ebi.ac.uk/ontology-lookup/?termId=MI:0915 with http://www.uniprot.org/uniprot/O43707 by http://www.ebi.ac.uk/ontology-lookup/?termId=MI:0018 (http://www.ebi.ac.uk/intact/interaction/EBI-9512145, http://www.ebi.ac.uk/intact/interaction/EBI-9512095) •http://www.uniprot.org/uniprot/C9S3S8 http://www.ebi.ac.uk/ontology-lookup/?termId=MI:0915 with http://www.uniprot.org/uniprot/O43707 by http://www.ebi.ac.uk/ontology-lookup/?termId=MI:0006 (http://www.ebi.ac.uk/intact/interaction/EBI-9513909)