Human erythrocyte and endothelial cells contain tbs ce transglutaminase that can regulates inflammation a nd platelet function by binding and releasing nitric oxde

Nitric oxide (NO) plays an important role in vascular biology. NO modifies proi eins through nitrosylation of free cysteine residues and such modifications play an impo tant role in signaling and protein function. Tissue transglutaminase (tTG) is an extracellul ir as well as intracellular enzyme that is expressed in erythrocytes, bone marrow stem cells and endothelial cells. Tissue TG exhibits a Ca2-dependent transglutaminase activity (TC ase) that cross-links proteins and is involved in wound healing, tissue remodeling and extrace] ular matrix (ECM) stabilization. Since tTG is in close proximity to sites of NO produc tion, has 18 free cysteine residues and also utilizes cysteine for catalysis, we investigated whether NO could bind and regulate tTG activity. In addition, the effects of nitrosylution of tTG on platelet aggregation and leukocyte adhesion to endothelial cells were also investigated. We report that TGase activity is regulated by NO through an unique Ca2dependent mechanism. Tissue TG can be polynitrosylated by the NO-carrier, snitrosocysteine (CysNO). In the absence of Ca2, up to eight cysteines were nitrosy ated and the nitrosylation did not modify TGase activity. However, tTG nitrosylated in the absence of Ca2 was 6-fold more susceptible to inhibition by Mg-GTP. Further, Ca'2 caused release of NO from nitrosylated tTG by an allosteric mechanism. The cys :eine residue that regulated the calcium dependent release of NO was localized to Cys521. In the presence of Ca2, up to 15 cysteines were found to be nitrosylated and this modifie ition resulted in an inhibition of TGase activity. When endothelial cells in culture were incu lated with tTG and stimulated to produce NO, the exogenous tTG was S-nitrosylated. In vivo and upon shear-activation of endothelial cells, NO groups are bound by cysteine thic Is of tTG. Furthermore, nitrosylated tTG (240 nM) inhibited platelet aggregation induce d by ADP. In conclusion, we provide evidence that Ca2 plays an important role in the bin ling, release, and inactivation of tTG by NO. This demonstrates a novel role for d 2 in regulating the biochemical and biologic function of tTG in vascular biology. The re le of tTG as a regulator of NO trafficking within the cytoplasm of erythrocytes and the ;CM of vascular tissue is currently under investigation.

Duke Scholars

Author Mark Wesley Dewhirst Radiation Oncology