Article

New regulatory mechanisms for the intracellular localization and trafficking of influenza A virus NS1 protein revealed by comparative analysis of A/PR/8/34 and A/Sydney/5/97.

State Key Laboratory of Virology, Wuhan Institute of Virology, Chinese Academy of Sciences Wuhan 430071, PR China.
Journal of General Virology (impact factor: 3.36). 12/2010; 91(Pt 12):2907-17. DOI:10.1099/vir.0.024943-0
Source: PubMed

ABSTRACT During influenza A virus infection, the NS1 protein is engaged in different functions in different intracellular compartments. In this study, we showed that the NS1 of A/PR/8/34 localized in different positions from that of A/Sydney/5/97 when transiently expressed in Madin-Darby canine kidney cells. Residue 221 of NS1 was identified to be a new key residue involved in the C-terminal nuclear localization signal (NLS) and nucleolar localization signal (NoLS) of NS1 from A/Sydney/5/97. Analysis of chimeric NS1 and further mutants showed that residues responsible for the binding between NS1 and the cleavage and polyadenylation specificity factor (CPSF) are correlated with the intracellular localization of transiently expressed NS1 proteins. Fluorescence loss in photobleaching imaging revealed that the NS1 protein with both functional NLSs and nuclear export signal (NES) was able to shuttle between the nucleus and cytoplasm. Drug inhibition experiments and fluorescence resonance energy transfer analysis suggested that NS1 was exported out of the cell nuclei via a Crm1-independent pathway. Moreover, it is likely that another cytoplasmic localization-related sequence exists in the NS1 protein other than the leucine-rich NES. These findings provide new insights into the mechanism of intracellular localization and trafficking of influenza A virus NS1 protein, which is important for understanding its function.

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    Article: Non-structural protein 1 of avian influenza A viruses differentially inhibit NF-κB promoter activation.
    Muhammad Munir, Siamak Zohari, Mikael Berg
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    ABSTRACT: Influenza virus infection activates NF-κB and is a general prerequisite for a productive influenza virus infection. On the other hand, non-structural protein 1 (NS1) suppresses this viral activated NF-κB, presumably to prevent expression of NF-κB mediated anti-viral response. NS1 proteins of influenza A viruses are divided into two groups, known as allele A and allele B. The possible functional relevance of this NS1 division to viral pathogenicity is lacking. The ability of NS1 protein from two avian influenza subtypes, H6N8 and H4N6, to inhibit NF-κB promoter activation was assessed. Further, efforts were made to characterize the genetic basis of this inhibition. We found that allele A NS1 proteins of H6N8 and H4N6 are significantly better in preventing dsRNA induced NF-κB promoter activation compared to allele B of corresponding subtypes, in a species independent manner. Furthermore, the ability to suppress NF-κB promoter activation was mapped to the effector domain while the RNA binding domain alone was unable to suppress this activation. Chimeric NS1 proteins containing either RNA binding domain of allele A and effector domain of allele B or vice versa, were equally potent in preventing NF-κB promoter activation compared to their wt. NS1 protein of allele A and B from both subtypes expressed efficiently as detected by Western blotting and predominantly localized in the nucleus in both A549 and MiLu cells as shown by in situ PLA. Here, we present another aspect of NS1 protein in inhibiting dsRNA induced NF-κB activation in an allele dependent manner. This suggests a possible correlation with the virus's pathogenic potential.
    Virology Journal 08/2011; 8:383. · 2.34 Impact Factor
Data provided are for informational purposes only. Although carefully collected, accuracy cannot be guaranteed. The impact factor represents a rough estimation of the journal's impact factor and does not reflect the actual current impact factor. Publisher conditions are provided by RoMEO. Differing provisions from the publisher's actual policy or licence agreement may be applicable.

Keywords

cell nuclei
 
chimeric NS1
 
Crm1-independent pathway
 
cytoplasmic localization-related sequence
 
different functions
 
different intracellular compartments
 
different positions
 
fluorescence resonance energy transfer analysis
 
Madin-Darby canine kidney cells
 
new insights
 
new key residue
 
NS1 protein
 
NS1 proteins
 
nuclear export signal
 
nucleolar localization signal
 
photobleaching imaging
 
polyadenylation specificity factor
 
residues responsible
 
virus infection
 
virus NS1 protein
 

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