Induction of IL-8 release in lung cells via activator protein-1 by recombinant baculovirus displaying severe acute respiratory syndrome-coronavirus spike proteins: Identification of two functional regions

The inflammatory response and the intracellular signaling pathway induced by severe acute respiratory syndrome (SARS)-coronavirus (CoV) were studied in lung epithelial cells and fibroblasts. SARS-CoV spike (S) protein-encoding plasmid induced activations of IL-8 promoter and AP-1, but not NF-kappaB in these cells. Mutation of the AP-1, not the kappaB site, abolished the SARS-CoV S protein-induced IL-8 promoter activity. IL-8 release was effectively induced by vAtEpGS688, a baculovirus exhibiting the aa 17-688 fragment of S protein, and this induction was attenuated by the angiotensin-converting enzyme 2 Ab. Recombinant baculovirus expressing different deletion and insertion fragments identified the functional region of S protein from aa 324-688 (particularly the N-terminal aa 324-488 and the C-terminal aa 609-688), which is responsible for IL-8 production. Activations of AP-1 DNA-protein binding and MAPKs after vAtEpGS688 transduction were demonstrated, and SARS-CoV S protein-induced IL-8 promoter activity was inhibited by the specific inhibitors of MAPK cascades. These results suggested that the S protein of SARS-CoV could induce release of IL-8 in the lung cells via activations of MAPKs and AP-1. The identification of the functional domain for IL-8 release will provide for the drug design on targeting specific sequence domains of S protein responsible for initiating the inflammatory response.