HIGH-LEVELS OF TRANSGLUTAMINASE EXPRESSION IN DOXORUBICIN-RESISTANT HUMAN BREAST-CARCINOMA CELLS

Tissue type II transglutaminase (TGase) is a member of the TGase family that catalyzes Ca2+-dependent covalent cross-linking of several amines to the gamma-carboxamide group of protein-bound glutamine residues. The degree of therapeutic efficacy or toxicity of drugs may be related to their ability to serve as a substrate for TGase and their covalent linkage to glutamine residues of regulatory proteins through the catalytic action of this enzyme. Here, doxorubicin (adriamycin)-resistant human breast carcinoma MCF-7(ADR) cells exhibited 40- to 60-fold higher TGase activity than control drug-sensitive MCF-7(WT) cells. The same was observed in vivo: a small proportion of tumor cells became positive for TGase after administration of adriamycin-based chemotherapy to patients with breast carcinoma. Similarly, continuous culture of MCF-7(WT) cells in the presence of adriamycin led to the appearance of the drug-resistant phenotype that was in turn associated with increased expression of TGase. This increase in TGase was specific for adriamycin resistance. Like most known TGases, MCF-7(ADR) TGase was completely dependent on the presence of Ca2+ for its catalytic activity. Based on its immunoreactivity, the TGase in MCF-7(ADR) cells was identified as an 85-kDa tissue-type TGase and was that the increase in TGase activity was due to accumulation of the protein. Two cytosolic proteins of approximately 20 and 30 kDa in MCF-7 cells served as suitable acyl donor substrates in TGase-catalyzed reactions. (C) Wiley-Liss, Inc.