Transglutaminase 2 is secreted from smooth muscle cells by transamidation-dependent microparticle formation
||J. van den Akker, A. van Weert, G. Afink, E.N.T.P. Bakker, E. van der Pol, A.N. Böing, R. Nieuwland, and E. van Bavel|
||Published August 10, 2011|
||Transglutaminase, microparticle, smooth muscle cell, GFP, flow cytometry|
||van den Akker 2012 Amino Acids Transglutaminase 2.pdf (778 kB)|
||van den Akker 2012 Amino Acids Transglutaminase 2 Supp.pdf (468 kB)|
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.