Transfection of influenza A virus nuclear export protein induces the expression of tumor necrosis factor alpha

•The role of influenza virus NEP and NS1 proteins on TNF-α expression was analyzed.•Transient transfection was performed to express NS1 and NEP proteins.•NEP but not NS1 induced TNF-α biosynthesis through promoter activation.•TNF-α promoter activation is reduced by Raf/MEK/ERK and NF-kB inhibitors.•We propose a new role for NEP in the transcriptional regulation of TNF-α expression.

Influenza A virus genomic segments eight codes for non-structural 1 (NS1) protein that is involved in evasion of innate antiviral response, and nuclear export protein (NEP) that participates in the export of viral ribonucleoprotein (RNP) complexes, transcription and replication. Tumor necrosis factor alpha (TNF-α) is highly expressed during influenza virus infections and is considered an anti-infective cytokine. NS1 and NEP proteins were overexpressed and their role on TNF-α expression was evaluated. Both TNF-α mRNA and protein increased in cells transfected with NEP but not with NS1. We further investigate if NS1 or NEP regulates the activity of TNF-α promoter. In the presence of NEP the activity of TNF-α promoter increased significantly compared with the control (83.5 ± 2.9 vs. 30.9 ± 2.8, respectively; p = 0.001). This effect decreased 15-fold when the TNF-α promoter distal region was deleted, suggesting the involvement of mitogen-activated protein kinases (MAPK) and NF-kB response elements. This was corroborated by testing the effect produced on TNF-α promoter by the treatment with Raf/MEK/ERK (U0126), NF-kB (Bay-11-7082) and PI3K (Ly294-002) cell signaling inhibitors. Treatment with U0126 and Bay-117082 reduced the activity of TNF-α promoter mediated by NEP (41.5 ± 3.2, 70% inhibition; and 80.6 ± 7.4, 35% inhibition, respectively) compared to mock-treated control. The results suggest a new role for NEP protein that participates in the transcriptional regulation of human TNF-α expression.