Requirement for transglutaminase in the activation of latent transforming growth factor-β in bovine endothelial cells

Abstract

A hitherto unknown function for transglutaminase (TGase; R-glutaminyl- peptide: amine γ-glutamyltransferase, EC 2.3.2.13) was found in the conversion of latent transforming growth factor-β (LTGF-β) to active TGF- β by bovine aortic endothelial cells (BAECs). The cell-associated, plasmin- mediated activation of LTGF-β to TGF-β induced either by treatment of BAECs with retinoids or by cocultures of BAECs and bovine smooth muscle cells (BSMCs) was blocked by seven different inhibitors of TGase as well as a neutralizing antibody to bovine endothelial cell type II TGase. Control experiments indicated that TGase inhibitors and/or neutralizing antibody to TGase did not interfere with the direct action of TGF-β, the release of LTGF-β from cells, or the activation of LTGF-β by plasmin or by transient acidification. After treatment with retinoids, BAECs expressed increased levels of TGase coordinate with the generation of TGF-β, whereas BSMCs and bovine embryonic skin fibroblasts, which did not activate LTGF-β after treatment with retinoids, did not. Furthermore, both TGase inhibitors and a neutralizing antibody to TGase potentiated the effect of retinol in enhancing plasminogen activator (PA) levels in cultures of BAECs by suppressing the TGF-β-mediated enhancement of PA inhibitor-1 (PAI-1) expression. These results indicate that type II TGase is a component required for cell surface, plasmin-mediated LTGF-β activation process and that increased expression of TGase accompanies retinoid-induced activation of LTGF-β.