Nitric oxide induces SOCS-1 expression in human monocytes in a TNF-alpha-dependent manner |
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Authors: | González-León M Carmen Soares-Schanoski Alessandra del Fresno Carlos Cimadevila Agata Goméz-Piña Vanesa Mendoza-Barberá Elena García Felipe Marín Elvira Arnalich Francisco Fuentes-Prior Pablo López-Collazo Eduardo |
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Affiliation: | Research Unit, La Paz Hospital, Madrid, Spain. |
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Abstract: | In contrast to the thoroughly characterized mechanisms of positive regulation within cytokine signaling pathways, our knowledge of negative feedback loops is comparatively sparse. We and others have previously reported that IRAK-M down-regulates inflammatory responses to multiple stimuli. In particular, we could show that the nitric oxide (NO) donor, GSNO, induces IRAK-M overexpression in human monocytes. Here we study the expression of another important negative regulator of cytokine signaling, SOCS-1, in human monocytes exposed to GSNO. The NO donor induced significant levels of SOCS-1 mRNA and protein, 6 h and 16 h after stimulation, respectively. Monocytes stimulated with GSNO for longer periods (24 h and 48 h) failed to express IL-6 and IP-10 upon LPS challenge. In addition, and in line with previous reports of NO-mediated induction of TNF-alpha, we have found that exposure to this cytokine induces SOCS-1 mRNA in human monocytes. A blocking antibody against TNF-alpha impaired SOCS-1 expression upon GSNO treatment and re-instated IL-6 and IP-10 mRNA levels after LPS challenge in cultures pretreated with the NO donor. We conclude that NO stimulates SOCS-1 overexpression in a pathway at least partially regulated by TNF-alpha. |
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