Identification of GPI-anchored protein releasing factor using GPI-anchored GFP

点击翻译按钮获取中文摘要

To clarify the fate of glyeosylphosphstidylinositol (GPI) in mammals, we developed GPI-anchored green fluorescent protein (GFP-GPI) and transgenic mice carrying this fusion constract. When it was introduced to culture cells, the GFP-GPI protein was correctly sorted to plasma membranes and mierosomes depending on GPI biosynthesis. Transgenic mice carrying GFP-GPI were found to show a broad transgene expression. Historogically, a prominent polarized localization of GFP-GPI protein was observed in various epithelia, nervous system and liver, as well as non-polarized presence in non-epthelial tissues.Surprisingly, the GFP-GPI protein showed high level secretion in exocrine glands and testis. What is the biological significance of this phenotype? How are GPI-anchored proteins released from membranes? To answer to these questions, we attempted to isolate which converts GPI-anchored proteins from the membrane attached form to the soluble form.Processing and turnover of transmembrane polypeptides and extra-cellular matrix proteins are performed by particular metalloproteases, contributing to multiple biological processes at the cell surface. However the regulation of -anchored proteins, a class of proteins anchoring to the outer-leaflet of membrane lipid bilayer via glycophospholipid moiety, was not further clarified.Here we found a metalloprotease, the angiotensin converting enzyme (ACE), release GPI-anchored proteins from the cell surface. ACE known to be a key regulator of blood pressure homeostasis cleaves various soluble small peptides, notably angiotensin I and bradykinin, thereby changing their biological activities and leading up-regulation of the blood pressure. The novel activity we found here suggests that ACE also contributes to membrane protein turnover and acts on more broad biological processes.