Article
Characterisation of the secretion pathway of Guanylate Binding Protein-1
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Published: | April 16, 2008 |
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Introduction: The guanylate binding protein-1 (GBP-1) belongs to the family of large GTPases which consists of 7 highly homologous proteins. The best characterized member of this family is GBP-1. The crystal structure of GBP-1 shows that the protein consists of two different domains, a N-terminal globular domain and a C-terminal helical domain. GBP-1 can be induced by interferon (IFN)-γ in many different cell types in vitro but is almost exclusively expressed in endothelial cells (EC) in vivo. In EC GBP-1 shows a granular cytoplasmic distribution which is a characteristic feature of secreted proteins.
Materials and methods: Recombinant expression of different proteins in primary EC, immunoprecipitation, immunoblotting, ELISA
Results: We found that GBP-1 is secreted from IFN-γ-stimulated EC in a time and concentration dependent manner. GBP-1 secretion was inhibited with glyburide, an inhibitor of alternative secretion pathways via ABC-transporters, but not with monensin, an inhibitor of the classical secretion pathway. GBP-1 was selectively secreted from EC but not from fibroblasts, smooth muscle cells or keratinocytes. Furthermore, GBP-1 was the only secreted member of the GBP-family. Important motifs regulating the secretion of GBP-1 were identified via expression of different mutants of GBP-1 in EC.
Conclusion: GBP-1 is the first GTPase which was found to be secreted from eukaryotic cells. It will be of high interest to investigate the extracellular functions of secreted GBP-1 in the future.