Molecular characterization of the bovine IER3 gene: Down-regulation of IL-8 by blocking NF-κB activity mediated by IER3 overexpression in MDBK cells infected with bovine viral diarrhea virus-1

The immediate early response 3 (IER3) is a key regulatory factor in the immune response, particularly as related to homeostasis immunomodulation via the nuclear factor kappa B (NF-κB) signaling pathway. The IER3 gene has been identified in mammals and, more recently, in other higher vertebrates. Nevertheless, relatively little is known about this regulator in bovines. Therefore, this study explored, characterized, and compared the genetic context of bovine IER3 to homologous genes in the human, mouse, and canine chromosomes. In silico analysis identified several regions of interest preserved in phylogenetically distant species. Similar analyses were also conducted for interleukin-8, a cytokine in which several putative cis elements were identified for the inducible transcription factor NF-κB. Subsequent challenge assays against the bovine viral diarrhea virus-1 revealed NF-κB signaling pathway activation just 15 min post-infection, a process blocked by the BAY-117085 inhibitor. Similarly, infection strongly increased IER3 expression. Interestingly, IER3 down-regulated interleukin-8 expression, as confirmed by IER3 gene inhibition using small interfering RNA, RT-qPCR, and luciferase assays. In conclusion, this is the first report to present data indicating that bovine IER3 is a strong regulator of immune-marker expression, specifically modulating bovine interleukin-8 activation through the NF-κB/IER3 pathway in response to the bovine viral diarrhea virus.