Year: 2007
Type: article
Abstract: Extracellular localization of epimorphin/syntaxin-2In a recent article, Flaumenhaft et al 1 showed that syntaxin-2 is found on the extracellular cell surface on activated platelets.While they conclude that theirs is the first demonstration of extracellular presentation of a syntaxin molecule, it should be noted that the syntaxin-2 protein is identical to epimorphin, which was identified first in 1992 as an extracellular morphogen through the use of function-blocking antibodies in lung and skin organ culture assays 2 and then in 1993 renamed as syntaxin-2, a member of the SNARE family of proteins that mediates intracellular vesicle fusion.3 As an extracellular morphogen, epimorphin has been found to be associated with the extracellular cell surface and also as a secreted molecule, acting to influence developmental processes of a wide variety of tissues including lung, mammary gland, liver, intestine, pancreas, cartilage, and hair follicle.2,[4][5][6][7][8] The function of platelet cell surface epimiorphin/syntaxin-2 is unclear.In the cytoplasm, epimorphin/syntaxin-2 is localized to the inner surface of the plasma membrane as a target SNARE (t-SNARE) and acts to mediate fusion with vesicles that possess the appropriate vesicle SNARE (v-SNARE) proteins.9 Flaumenhaft et al 1 suggest that platelet cell surface epimorphin/syntaxin-2 may play a role analogous with its intracellular function, perhaps by mediating cell-cell fusion events.To accomplish this, the target cells would also need to present extracellular v-SNARE proteins and, to date, there are no indications for extracellular presentation of v-SNARE proteins.Another possibility is that platelet cell surface epimorphin/syntaxin-2 may function as an adhesive or signaling molecule, as it functions in many other cell types.2,[4][5][6][7] Epimorphin/syntaxin-2 has been found to bind ␣V5 and ␣V1 integrins on target epithelial cells and to initiate specific signaling processes 10 ; platelet cell surface epimorphin may similarly facilitate adhesion and/or cell signaling processes with endothelial or other cell types through association with cell surface integrins on these target cells.In either case, the recent studies of Flaumenhaft et al are a key first step in the elucidation of platelet-specific functions controlled by this intriguing molecule.
Source: Blood
Authors: Yohei Hirai, Mina J. Bissell, Derek C. Radisky
Institution: Kyoto University
Language: English
Subfield: Cell Biology
Domain: Life Sciences
Open Access status: bronze
OpenAlex ID: W1998365487