title: Transglutaminase 2 is secreted from smooth muscle cells by transamidation-dependent microparticle formation.
abstract: Transglutaminase 2 (TG2) is a pleiotropic enzyme involved in both intra- and extracellular processes. In the extracellular matrix, TG2 stabilizes the matrix by both covalent cross-linking and disulfide isomerase activity. These functions become especially apparent during matrix remodeling as seen in wound healing, tumor development and vascular remodeling. However, TG2 lacks the signal sequence for a classical secretory mechanism, and the cellular mechanism of TG2 secretion is currently unknown. We developed a green fluorescent TG2 fusion protein to study the hypothesis that TG2 is secreted via microparticles. Characterization of TG2/eGFP, using HEK/293T cells with a low endogenous TG2 expression, showed that cross-linking activity and fibronectin binding were unaffected. Transfection of TG2/eGFP into smooth muscle cells resulted in the formation of microparticles (MPs) enriched in TG2, as detected both by immunofluorescent microscopy and flow cytometry. The fraction of TG2-positive MPs was significantly lower for cross-linking-deficient mutants of TG2, implicating a functional role for TG2 in the formation of MPs. In conclusion, the current data suggest that TG2 is secreted from the cell via microparticles through a process regulated by TG2 cross-linking.
authors.affiliation: Departmentt of Biomedical Engineering and Physics, Academic Medical Center L0-120, University of Amsterdam, PO Box 22660, 1100 DD, Amsterdam, The Netherlands.
authors.forename: Jeroen
authors.initials: J
authors.lastname: van den Akker
authors.forename: Angela
authors.initials: A
authors.lastname: van Weert
authors.forename: Gijs
authors.initials: G
authors.lastname: Afink
authors.forename: Erik N T P
authors.initials: EN
authors.lastname: Bakker
authors.forename: Edwin
authors.initials: E
authors.lastname: van der Pol
authors.forename: Anita N
authors.initials: AN
authors.lastname: Böing
authors.forename: Rienk
authors.initials: R
authors.lastname: Nieuwland
authors.forename: Ed
authors.initials: E
authors.lastname: VanBavel
mesh_terms: D000577:Amides / Q000378:metabolism*; D002460:Cell Line; D005353:Fibronectins / Q000378:metabolism; D005434:Flow Cytometry; D005456:Fluorescent Dyes; D019204:GTP-Binding Proteins / Q000378:metabolism*; D006801:Humans; D009130:Muscle, Smooth / Q000166:cytology / Q000378:metabolism*; D000091345:Protein Glutamine gamma Glutamyltransferase 2; D013347:Subcellular Fractions / Q000201:enzymology; D011503:Transglutaminases / Q000378:metabolism*
chemical_list: D000577:Amides; D005353:Fibronectins; D005456:Fluorescent Dyes; D000091345:Protein Glutamine gamma Glutamyltransferase 2; D011503:Transglutaminases; D019204:GTP-Binding Proteins