The Influenza A Virus Non‐structural Protein NS 1 Upregulates The Expression of Collagen Triple Helix Repeat Containing 1 Protein

Influenza A virus ( IAV ) infection induces a strong immune response and regulates the expression of many host proteins. The collagen triple helix repeat containing 1 ( CTHRC 1) protein is a secreted protein that exhibits increased expression during the viral infection process. However, the regulatory function of IAV on CTHRC 1 expression is obscure. In this study, we investigated the effect of IAV on CTHRC 1 expression and its regulatory mechanism. A total of 106 serum specimens from healthy people and 80 serum specimens from patients infected with IAV were collected. The CTHRC 1 levels in the sera from the IVA patients and healthy individuals were measured using an enzyme‐linked immunosorbent assay ( ELISA ), and the differences were statistically analysed. A549 cells were infected with the IAV or del NS 1 virus. Additionally, A549 cells were cotransfected with a eukaryotic non‐structural NS 1 protein gene expression plasmid and the CTHRC 1 gene promoter reporter plasmid ( pCTHRC 1‐Luc), and, the luciferase activities were assessed. The CTHRC 1 mRNA and protein expression were detected using reverse transcription–polymerase chain reaction ( RT ‐ PCR ) and Western blotting, respectively. The serum CTHRC 1 level was significantly higher in the IAV patients than in the healthy individuals. IAV upregulated the CTHRC 1 mRNA and protein expression. The non‐structural NS 1 protein specifically activated CTHRC 1 gene promoter activity and upregulated CTHRC 1 mRNA and protein expression. The activation function had a dose‐dependent effect, indicating that influenza virus upregulated CTHRC 1 expression through its NS 1 protein.