The existence of an inactive form of transglutaminase within metastasising tumours

Separation by anion exchange chromatography of detergent extracts from a poorly metastatic HSV-2-induced hamster fibrosarcoma, its highly metastatic variant and a highly metastatic rat fibrosarcoma indicated the presence of an inactive form of transglutaminase antigen, when eluent fractions were assayed for transglutaminase activity and antigen. This inactive antigenic transglutaminase was clearly separable from the particulate and cytosolic forms of the transglutaminase enzyme. Unlike tumours, its presence could not be demonstrated in extracts from normal rat liver. Measurement of activity levels during tumour growth indicated that the progression of the two highly metastatic tumours was accompanied by a decrease in cytosolic transglutaminase activity, whilst the activity of this enzyme form remained constant in the poorly metastatic tumour. Measurement of antigen levels indicated an inverse relationship between the level of inactive transglutaminase and the level of cytosolic transglutaminase activity, suggesting that the two forms are inter-related. Gel filtration indicated the molecular weight of the inactive form to be greater than both the particulate and cytosolic forms, and it was estimated to be 120,000. Partial proteolysis of the semi-purified inactive form, by either trypsin or thrombin, led to its activation and to the appearance of a transglutaminase similar in molecular weight and ionic mobility, both by anion-exchange chromatography and electrophoresis, to the cytosolic transglutaminase.