Influenza A virus nucleoprotein induces apoptosis in human airway epithelial cells: implications of a novel interaction between nucleoprotein and host protein Clusterin

S Tripathi,N J Cox,W Cao,S Sambhara,P Ranjan,R B Lal,S K Lal,J M Katz,K Sharma,J R Patel,J Batra,A Kumar

doi:10.1038/cddis.2013.89

Abstract

Apoptosis induction is an antiviral host response, however, influenza A virus (IAV) infection promotes host cell death. The nucleoprotein (NP) of IAV is known to contribute to viral pathogenesis, but its role in virus-induced host cell death was hitherto unknown. We observed that NP contributes to IAV infection induced cell death and heterologous expression of NP alone can induce apoptosis in human airway epithelial cells. The apoptotic effect of IAV NP was significant when compared with other known proapoptotic proteins of IAV. The cell death induced by IAV NP was executed through the intrinsic apoptosis pathway. We screened host cellular factors for those that may be targeted by NP for inducing apoptosis and identified human antiapoptotic protein Clusterin (CLU) as a novel interacting partner. The interaction between IAV NP and CLU was highly conserved and mediated through β-chain of the CLU protein. Also CLU was found to interact specifically with IAV NP and not with any other known apoptosis modulatory protein of IAV. CLU prevents induction of the intrinsic apoptosis pathway by binding to Bax and inhibiting its movement into the mitochondria. We found that the expression of IAV NP reduced the association between CLU and Bax in mammalian cells. Further, we observed that CLU overexpression attenuated NP-induced cell death and had a negative effect on IAV replication. Collectively, these findings indicate a new function for IAV NP in inducing host cell death and suggest a role for the host antiapoptotic protein CLU in this process.

Highlights

Many Influenza A viruses (IAVs) proteins such as PB1F2, NS1, M1, M2 and NA are known to modulate the host cell death, invariably by targeting cellular factors.[4,5,6,7,8,9,10] IAV nucleoprotein (NP) has been implicated in viral pathogenesis and host range determination;[11,12] there has been no report of its direct role in influenza virus-induced cell death
It interacts with a number of host cellular factors including nuclear import receptor a importin, nuclear export receptor CRM1, cytoskeletal element F actin and DEAD-box helicase BAT1/UAP56.12,18–20 All these known interactions of IAV NP have been implicated in the intracellular trafficking of the viral genome, viral RNA replication and virus assembly.[13]
Our results suggest a new role for IAV NP in host cell death induction, which is mediated by its interaction with the host antiapoptotic factor CLU

Summary

Introduction

Many IAV proteins such as PB1F2, NS1, M1, M2 and NA are known to modulate the host cell death, invariably by targeting cellular factors.[4,5,6,7,8,9,10] IAV nucleoprotein (NP) has been implicated in viral pathogenesis and host range determination;[11,12] there has been no report of its direct role in influenza virus-induced cell death. Viral proteins often modulate the host apoptotic responses through their interactions with cellular factors.[21] In a screen to identify cellular interactors of IAV NP, we found a novel and highly conserved interaction between IAV NP and host protein Clusterin (CLU). We found that IAV NP weakens the association between CLU

Methods

Results

Conclusion