The role of tissue transglutaminase active site mutants in the cell cycle and drug response

Renal cell carcinoma (RCC) accounting for 85 percent of all kidney cancer cases constitutes 2 percent of all cancer-related death worldwide. The rapid development of the disease and poor survival rate entitles RCC as one of the most prevalent and carcinogenic neoplasms in urologic diseases. Despite recent advances in cancer treatment, recurrence of tumor, chemoresistance, and metastasis remain to be significant consequences of aggressive RCC. As a result, new treatment alternatives that necessitate the discovery of novel therapeutic targets are still needed. From this point of view, tissue transglutaminase TG2 draws attention due to its role in the progression, development, survival of various neoplasms including RCC. TG2 can gain these roles owing to its enzymatic activities which are GTPase and transamidase activities. Accumulating evidence showed that the GTPase activity of TG2 mostly participates in anti-apoptotic functions in cells while transamidase activity of TG2 is generally required for its interaction with the cell adhesion receptors. Therefore, in this study, TG2-variants which are transamidase active type TG2-R580A, transamidase-deficient, and low GTP-binding active form TG2-C277S and GTP-binding-active TG2-W241A were expressed in the RCC cell line to elucidate the role of transamidase and GTP-binding function of TG2 in the regulation of cell cycle and drug resistance of RCC. Based on our data, catalytically inactive transamidase domain-containing but GTPase active form TG2-W241A expressing RenCa showed the highest cell proliferation rate and increased cell cycle profile. In addition, although being subjected to a well-known mTOR inhibitor, everolimus, TG2-W241A RenCa cells were the only group that was not cytotoxically affected by this drug treatment. The fact that TG2-W241A expressing cells continued to proliferate whilst being exposed to everolimus suggested that the GTP-binding activity of TG2 may be important in circumventing cell death. Overall, these findings showed for the first time the indispensable role of the GTP binding function of TG2 on cell proliferation and everolimus resistance in RCC. This project was funded by FP-7 TRANSPATH 289964 grants.