The guanylate binding protein-1

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 “EC activation”. 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. The 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. The
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. To 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. In
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’s sarcoma. This indicated that GBP-1
characterizes IC-activated EC in vivo. Further immunohistochemical
studies on Kaposi’s 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. Finally, 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 3 Summary 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–-therapy or in
patients with inflammatory diseases. These 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.