The role of tissue transglutaminase (dTG) in renal cell carcinoma cell adhesion and cell migration

Transglutaminase (TG2) catalyzes Ca+2 dependent post-translational modification of proteins by forming covalent ε (γ-glutamyl) lysine linkages. TG2 also plays an important role in cell adhesion and migration by acting as a novel adhesion protein interacting with integrins and syndecan-4 (SDC4). Together with β1 integrin (ITGB1), TG2 expression has been shown increase in cancers with epithelial origin providing an enhanced drug resistance and metastatic potential. Renal Cell Carcinoma (RCC) is a common type of epithelial cancer comprising 90% of kidney cancer cases. In primary RCC tumors TG2 expression was found to be decreased while an increase in association with ITGB1 and SDC4 expression was found to be evident in the metastatic RCC tumors. This thesis aims to dissect the molecular mechanisms of TG2-induced metastatic potential in RCC using model cell lines. For this purpose, in primary A-498, Caki-2 and metastatic ACHN, Caki-1 RCC cell lines the role of TG2 in RCC cell migration and invasion on ITGB1 specific substrates was examined using Wound Scratch and Transwell Invasion Assay, respectively. The role of TG2 in the focal contact formation and cell adhesion was also analyzed through actin-stress fiber staining with FITC-labeled Phalloidin. Results indicated that while the fastest migration potential was found to be in metastatic Caki-1 and ACHN, the silencing of TG2 decreased their migration potential by %50. Results from Transwell experiments indicated that primary Caki-2 cells possessed the highest migration potential on fibronectin, while the metastatic RCC cell lines demonstrated the highest migration on collagen type I and laminin. Down-regulation of TG2 using siRNA technology led to a significant 50%-60% decrease in the invasive potential of all RCC cell lines suggesting that TG2 is not only important in cell migration but also in intravasation and extravasation stages of metastasis.