Nitric oxide produces HLA-G nitration and induces metalloprotease-dependent shedding creating a tolerogenic milieu
Angel Díaz-Lagares (1), Estibaliz Alegre (1), Joel LeMaoult (2), Edgardo D. Carosella (2) and Álvaro González (1)
(1) Department of Biochemistry, University Clinic of Navarra, Pamplona, Spain
(2) Service de Recherches en Hémato-Immunologie, CEA-DSV-DRM, Institut Universitaire d?He´matologie, Hopital Saint Louis, Paris, France
Human leucocyte antigen G (HLA-G) is a tolerogenic molecule that protects the fetus from maternal immune attack, may favour tumoral immunoescape and is up-regulated in viral and inflammatory diseases. The aim of this work was to discover if nitric oxide (NO) could affect HLA-G expression or function because NO is an important modulator of innate and adaptive immunity.
For this purpose HLA-G expression and function were analysed following treatment with a NO donor or a peroxynitrite donor in various cell lines expressing HLA-G either spontaneously or upon transfection. Results showed NO-dependent nitration of both cellular and soluble HLA-G protein, but not all HLA-G moieties underwent nitration. Endogenous biosynthesis of NO by both U-937-HLA-G1 and M8-HLA-G5 stable transfectants also caused HLA-G nitration.
The NO decreased total HLA-G cellular protein content and expression on the cell surface, while increasing HLA-G shedding into the culture medium. This effect was post-transcriptional and the result of metalloprotease activity. By contrast, NO pretreatment did not affect HLA-G capability to suppress NK cytotoxicity and lymphocyte proliferation.
Our studies show that NO regulates the availability of HLA-G molecules without modifying their biological activities.
CITATION Immunology. 2009 Mar;126(3):436-45