Requirement for Transglutaminase in the Activation of Latent Transforming Growth Factor-/3 in Bovine Endothelial Cells

A hitherto unknown function for transglutaminase (TGase; R-glutaminyl-peptide: amine 3,-glutamyltransferase, EC 2.3.2.13) was found in the conversion of latent transforming growth factor-/3 (LTGF-/3) to active TGF-B by bovine aortic endothelial cells (BAECs). The cell-associated, plasmin-mediated activation of LTGF-/3 to TGF-13 induced either by treatment of BAECs with retinoids or by cocultures of BAECs and bovine smooth muscle ceils (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 a neutralizing antibody to TGase did not interfere with the direct action of TGF~, the release of LTGF-B from cells, or the activation of LTGF-B by plasmin or by transient acidification. After treatment with retinoids, BAECs expressed increased levels of TGase coordinate with the generation of TGF-B, whereas BSMCs and bovine embryonic skin fibroblasts, which did not activate LTGF-/3 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-B-mediated enhancement of PA inhibitor-I (PAl-I) expression. These results indicate that type II TGase is a component required for cell surface, plasmin-mediated LTGF-B activation process and that increased expression of TGase accompanies retinoid-induced activation of LTGF-13. T 1sstJ~ type II transglutaminase (TGase; R-glutaminylpeptide: amine -t-glutamyltransferase, EC 2.3.2.13) is a member of the TGase family that catalyze Ca2÷-de pendent acyl transfer reactions between -t-carboxamide groups of the glutamine residues in peptides and either primary amines or e-amino groups of the lysine residues in peptides, resulting in the formation of new "t-amides of glutamic acid or e-(-t-glutamyl)lysine bonds and ammonia (Folk, 1980; Lorand and Conrad, 1984; Greenberg etal., 1991). The molecular structure of type II TGase has been reported (Ikura et al., 1988; Gentile et al., 1991; Nakanishi et al., 1991). Type II TGase has a wide distribution; it is found in liver (Folk, 1980; Ikura et al., 1988), epidermal cells (Lichti etal., 1985), erythrocytes (Signorini et al., 1988), macrophages (Chiocca et al., 1989; Gentile etal., 1991), and many cancer cells including HL-60 myeloid cells (Chiocca et al., 1989). Furthermore, various organs express type II TGase (Folk, 1980) due to its occurrence in ubiquitous cell types such as endothelial ceils (ECs), smooth muscle cells (SMCs), and certain perivascular fibroblasts (Kojima et al,, 1987; Greenberg et al., 1987; Korner etal., 1989; Thom~y and Please address all correspondence to Dr. D. B. Rifkin, Department of Cell Biology, New York University School of Medicine, 550 First Avenue, New York, NY 10016. Fdstis, 1989; Gentile etal. , 1991). Whereas physiological roles of two types of TGases have definitively been described, e.g., the formation of cross-linkages between fibrin molecules by plasma Factor XIIIa (Lorand and Conrad, 1984; Greenberg etal., 1991) and the formation of cross-linked envelopes during epidermal cell differentiation by tissue type I TGase (Thacher and Rice, 1985), the physiological role of type II TGase has not yet been established except for the formation of cross-links in erythrocyte membrane proteins (Folk, 1980; Lorand and Conrad, 1984). One putative role for type II TGase is an involvement in the regulation of cell growth and differentiation (Birckbichler and Patterson, 1978; Chiocca etal., 1989; Suedhoffet al., 1990). This hypothesis was derived from the observation that when cellular TGase levels are high, cell growth is suppressed and/or cell differentiation is induced. In some of the experiments designed to test this hypothesis, cells were treated with retinoids, compounds that have profound effects on the regulation of cell growth and differentiation (Roberts and Sporn, 1984), to increase TGase levels. Recently, retinoids were also shown to increase the production of active TGF-/3 in osteoclasts (Oreffo et al., 1989), keratinocytes (Glick et al., 1989), and ECs (Kojima and Rifldn, 1993). The TGF-/~ family consists of a number of related, but functionally distinct, 25-kD homodimers © The Rockefeller University Press, 0021-9525/93/04/439/10 $2.00 The Journal of Cell Biology, Volume 121, Number 2, April 1993 439-448 439 on A ril 3, 2017 D ow nladed fom Published April 15, 1993