A novel role of the interferon-inducible protein IFI16 as inducer of proinflammatory molecules in endothelial cells.
The human IFI16 gene is an interferon-inducible gene implicated in the regulation of endothelial cell proliferation and tube morphogenesis. Immunohistochemical analysis has demonstrated that this gene is highly expressed in endothelial cells in addition to hematopoietic tissues. In this study, gene array analysis of human umbilical vein endothelial cells overexpressing IFI16 revealed an increased expression of genes involved in immunomodulation, cell growth, and apoptosis. Consistent with these observations, IFI16 triggered expression of adhesion molecules such as ICAM-1 and E-selectin or chemokines such as interleukin-8 or MCP-1. Treatment of cells with short hairpin RNA targeting IFI16 significantly inhibited ICAM-1 induction by interferon (IFN)-gamma demonstrating that IFI16 is required for proinflammatory gene stimulation. Moreover, functional analysis of the ICAM-1 promoter by deletion- or site-specific mutation demonstrated that NF-kappaB is the main mediator of IFI16-driven gene induction. NF-kappaB activation appears to be triggered by IFI16 through a novel mechanism involving suppression of IkappaBalpha mRNA and protein expression. Support for this finding comes from the observation that IFI16 targeting with specific short hairpin RNA down-regulates NF-kappaB binding activity to its cognate DNA and inhibits ICAM-1 expression induced by IFN-gamma. Using transient transfection and luciferase assay, electrophoretic mobility shift assay, and chromatin immunoprecipitation, we demonstrate indeed that activation of the NF-kappaB response is mediated by IFI16-induced block of Sp1-like factor recruitment to the promoter of the IkappaBalpha gene, encoding the main NF-kappaB inhibitor. Activation of NF-kappaB accompanied by induction of proinflammatory molecules was also observed when IkappaBalpha expression was down-regulated by specific small interfering RNA, resulting in an outcome similar to that observed with IFI16 overexpression. Taken together, these data implicate IFI16 as a novel regulator of endothelial proinflammatory activity and provide new insights into the physiological functions of the IFN-inducible gene IFI16.
Caposio
Patrizia
P
Department of Public Health and Microbiology, University of Turin, Turin, 10126, Italy.
Gugliesi
Francesca
F
Department of Public Health and Microbiology, University of Turin, Turin, 10126, Italy.
Zannetti
Claudia
C
Department of Public Health and Microbiology, University of Turin, Turin, 10126, Italy.
Sponza
Simone
S
Department of Public Health and Microbiology, University of Turin, Turin, 10126, Italy.
Mondini
Michele
M
Department of Public Health and Microbiology, University of Turin, Turin, 10126, Italy; Department of Clinical and Experimental Medicine, University of Piemonte Orientale, 28100 Novara, Italy.
Medico
Enzo
E
Institute for Cancer Research and Treatment, University of Turin, Turin 10126, Italy.
Hiscott
John
J
Lady Davis Institute, McGill University, Montreal H3T 1E2, Canada.
Young
Howard A
HA
Laboratory of Experimental Immunology, Center for Cancer Research, NCI-Frederick, National Institutes of Health, Frederick, Maryland 21702.
Gribaudo
Giorgio
G
Department of Public Health and Microbiology, University of Turin, Turin, 10126, Italy.
Gariglio
Marisa
M
Department of Clinical and Experimental Medicine, University of Piemonte Orientale, 28100 Novara, Italy.
Landolfo
Santo
S
Department of Public Health and Microbiology, University of Turin, Turin, 10126, Italy. Electronic address: santo.landolfo@unito.it.
D002460:Cell Line; D002467:Cell Nucleus / Q000378:metabolism; D049109:Cell Proliferation; D019281:Dimerization; D042783:Endothelial Cells / Q000378:metabolism*; D006801:Humans; D020672:I-kappa B Proteins / Q000378:metabolism; D018799:Intercellular Adhesion Molecule-1 / Q000378:metabolism; D007371:Interferon-gamma / Q000378:metabolism; D007372:Interferons / Q000378:metabolism*; D008954:Models, Biological; D000072000:NF-KappaB Inhibitor alpha; D016328:NF-kappa B / Q000378:metabolism; D009687:Nuclear Proteins / Q000378:metabolism*; D010750:Phosphoproteins / Q000378:metabolism*; D021381:Protein Transport; D034622:RNA Interference
D020672:I-kappa B Proteins; D016328:NF-kappa B; C000606204:NFKBIA protein, human; D009687:Nuclear Proteins; D010750:Phosphoproteins; D018799:Intercellular Adhesion Molecule-1; D000072000:NF-KappaB Inhibitor alpha; C076700:IFI16 protein, human; D007371:Interferon-gamma; D007372:Interferons