CHARACTERIZATION OF A TRANSGLUTAMINASE EXPRESSED IN HUMAN PANCREATIC ADENOCARCINOMA CELLS

A soluble tissue type transglutaminase (TGases; R-glutaminylpeptide:am ine gamma-glutamyltransferase, E.C.2.3.2.13) belonging to a group of w idely distributed enzymes which catalyze the reaction between a gamma- carboxyamide group of a protein-bound glutamine residue and various am ino groups was characterized in cell lines derived from human pancreat ic carcinoma. The enzyme activity was measured by incorporation of [H- 3]putrescine into N,N-dimethylcasein. It showed a strong dependency on Ca2+, which could not be replaced by Mg2+ but was 80% inhibited by 0. 7 mm Mg2+ in the presence of optimal Ca2+ concentration (7 mm). The Km -value in regard to putrescine was 2.6 mm. After centrifugation of cel l homogenates at 105000g 95% of the enzyme activity was found in the s upernatant indicating that the TGase in pancreatic tumor cells is solu ble. This was further substantiated by immunohistochemistry showing a homogenous cytoplasmic distribution of the TGase in pancreatic tumor c ells. Molecular sieve chromatography and Western blot analysis using a n antibody against TGase II from human erythrocytes revealed a molecul ar mass of 80 kDa. In Northern blots with a cDNA of TGase II from mous e macrophages a single transcript approximately 3.4 kbp in size was de tected. Polymerase chain reaction analysis using primers for the codin g and 3'-non-coding regions showed in each case a single product with the size expected from the human cDNA of TGase II. Taken these data to gether, we conclude that human pancreatic adenocarcinoma cells express the soluble tissue type TGase II. The enzyme activity of TGase in dif ferent pancreatic tumor cell lines varied between 1 unit to about 17 u nits and this was accompanied by corresponding amounts of protein or m RNA, respectively. This is the first time that a TGase is described an d characterized in human pancreatic adenocarcinoma cells which are der ived from the duct system of this gland. However, in contrast to other cellular systems, only a partial correlation between cellular differe ntiation or metastatic behavior of the tumor cells with their expressi on of TGase was observed.