The Nucleocapsid Protein of SARS-CoV Induces Transcription of hfgl2 Prothrombinase Gene Dependent on C/EBP Alpha

Fibrin deposition was universal in the lungs of SARS patients and fgl2 prothrombinase gene, a novel procoagulant, was demonstrated to express highly in a clinically relevant SARS model. To investigate whether and which structural protein of SARS-CoV induced transcription of hfgl2 prothrombinase gene, three eukaryotic expression plasmids expressing nucleocapsid protein (N), membrane protein (M) and spike protein 2 (S2) of SARS-CoV were co-transfected with hfgl2 promoter luciferase-reporter plasmids and beta-galactosidase plasmid in CHO cells, respectively. M, N and S2 protein of SARS-CoV were detected by western blotting and immunohistochemistry analysis. Further assays demonstrated that expression of hfgl2 gene was related with N protein, but not with M or S2 protein in THP-1 cells and Vero cells. N protein significantly induced functional procoagulant activity in comparison with control group. Luciferase assay showed that N protein of SARS-CoV could activate the transcription of hfgl2 promoter compared with the pcDNA3.1 empty vector. Site-directed mutagenesis and EMSA assay further demonstrated that transcription factor C/EBP alpha band with its cognate cis-element in hfgl2 promoter. The results showed that N protein of SARS-CoV induced hfgl2 gene transcription dependent on the transcription factor C/EBP alpha, which maybe contribute to the development of thrombosis in SARS.