Transglutaminase 2 is secreted from smooth muscle cells by transamidation-dependent microparticle formation

• DOI: 10.1007/s00726-011-1010-3
• Publication Date: 2011-08-09T11:42:07Z
• Authors: Jeroen van den Akker; Angela van Weert; Gijs Afink; Erik N. T. P. Bakker; Edwin van der Pol; Anita N. Böing; Rienk Nieuwland; Ed VanBavel
• Keywords: 0301 basic medicine; Transglutaminases; Organic Chemistry; Clinical Biochemistry; Muscle, Smooth; Flow Cytometry; Biochemistry; Amides; Cell Line; Fibronectins; 03 medical and health sciences; GTP-Binding Proteins; Humans; Original Article; Protein Glutamine gamma Glutamyltransferase 2; Fluorescent Dyes; Subcellular Fractions

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.