Abstract
ABSTRACTTissue transglutaminase (TG2) is the ubiquitously expressed member of transglutaminase family and shown to play a critical role in the development and progression of drug resistance malignancies. We have previously showed the association of TG2 upregulation with progression and metastasis of renal cell carcinoma (RCC) and low disease-free survival. In the present study we further investigate the role of TG2 in cell adhesion, migration and invasion of RCC by silencing TG2 expression in Caki-2 and A-498 primary site and Caki-1 and ACHN metastatic site RCC cell lines. Downregulation of TG2 expression led up to a 60% decrease in actin stress fiber formation and adhesion to β 1 integrin (ITGB1) substrates fibronectin, collagen type I and laminin in both primary and metastatic site RCC cell lines. In addition, treatment with siRNAs against TG2 impaired the migration capacity and cellular invasiveness of ITGB1 substrates in all 4 RCC cell lines. Lastly, the knockdown of TG2 in metastatic Caki-1 cells diminished the expression of CD44, CD73-and CD105 cancer stem cell-like markers. We conclude, for the first time, that TG2 expression is critical for cancer cell adhesion, migration, invasiveness and cancer cell-stemness during RCC progression and dissemination. Therefore, combined targeting of TG2 with drugs widely used in the treatment of RCC may be a promising therapeutic strategy for RCC.
Highlights
Tumor cell migration and invasion can transform a primary tumor into a metastatic and life-threatening disease, which is mostly resistant to therapeutic agents
Given that TG2 cooperatively operates with b 1 integrins in the organization of cell adhesion and migration,[6,9] here we have further investigated the main role of TG2 in cell adhesion, migration and invasion of renal cell carcinoma (RCC) using primary site A-498 and Caki-2 and metastatic site Caki-1 and ACHN RCC cell lines. siRNA downregulation of TG2 was performed to assess the significance of TG2 in cell adhesion, migration and invasion of all 4 RCC cell lines on b 1 integrin substrates of FN, collagen type I (Col1) and laminin (LM)
Endogenous TG2 was silenced in these cell lines using targeted siRNAs and the formation of actin stress fibers in TG2 knockdown cells were analyzed by fluorescence microscopy using FITC-phalloidin staining
Summary
Tumor cell migration and invasion can transform a primary tumor into a metastatic and life-threatening disease, which is mostly resistant to therapeutic agents. TG2s other pleiotropic functions include GTPase/ATPase, protein disulfide isomerase, and protein kinase activity.[6,8] independent from its catalytic activity, TG2 once bound to FN can act as a ligand for the heparan sulfate chains of syndecan-4 (SDC4) and lead to the activation of b1 integrin (ITGB1) through inside-out signaling.[9]
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