The guanylate binding protein-1
b'The endothelium is among the largest organs in the body. Stimuli originating from the blood or from neighbouring cells, like inflammatory cytokines (IC), lead to structural and functional alterations of vascular endothelial cells (EC). These alterations are often referred to as \\u201cEC activation\\u201d. Activated EC play a key role in different physiological processes like during immune response, in menstruation and in pathological processes like inflammation, allergy, viral infections, atherosclerosis and tumour angiogenesis.\\nThe human guanylate binding protein-1 (GBP-1) is a protein of the family of large GTPases. GBP-1 is characterized by a high turnover GTPase activity. Previous work showed that GBP-1 mRNA expression is induced by IC in EC and that GBP-1 is the specific mediator of the anti-proliferative effect of IC on EC in vitro.\\nThe main goals of this work were first, to investigate whether GBP-1 may be a molecular marker of IC-activated EC at the protein level in vitro. Second, to investigate GBP-1 expression in human healthy and/or disease tissues and to determine whether GBP-1 may be a molecular marker of IC-activated EC in vivo.\\nTo this goal mono- and poly-clonal antibodies against GBP-1 were generated. In vitro studies showed that GBP-1 expression in EC is induced by IFN-, IFN-, IL-1, IL-1 or TNF- but not by other cytokines, chemokines or growth factors. Moreover, simultaneous addition of bFGF and VEGF and IC reduced the IC-induced GBP-1 expression. This indicated that GBP-1 characterizes cells that are preferentially exposed to IC.\\nIn vivo studies using immunohistochemistry and immunofluorescence showed that GBP-1 expression is highly associated with vascular EC in a broad range of human tissues. This was confirmed by the simultaneous detection of GBP-1 and the EC-associated marker CD31. Notably, GBP-1 expression was undetectable in healthy skin. In contrast, GBP-1 was highly expressed in vessels of skin diseases with a high inflammatory component including psoriasis, adverse drug reactions and Kaposi\\u2019s sarcoma. This indicated that GBP-1 characterizes IC-activated EC in vivo. Further immunohistochemical studies on Kaposi\\u2019s sarcoma demonstrated that GBP-1 expression and EC cell proliferation are inversely related. This indicated that GBP-1 may also mediate the anti-proliferative effect of IC on EC in vivo.\\nFinally, GBP-1 was found to be secreted by EC stimulated with IFN- and IFN- in vitro. This finding was confirmed by immunoprecipitation of GBP-1 from cell culture supernatants and by a novel ELISA developed for the detection of GBP-1 in solution. Further characterization of the mechanism of secretion demonstrated that GBP-1 release is due to an\\n3\\nSummary energy-dependent mechanism and is not due to cell death. Most importantly, circulating GBP-1 could be detected in increased concentrations in the blood of patients that were subjected to IFN\\u2013-therapy or in patients with inflammatory diseases.\\nThese findings indicated that GBP-1 is a novel marker of inflammatory vessel activation. Specifically, the serological detection of GBP-1 may open new perspectives for the early detection of inflammatory activation of EC in patients with inflammatory diseases.'