miR-17 inhibition enhances the formation of kidney cancer spheres with stem cell/tumor initiating cell properties

// Zsuzsanna Lichner 1,2 , Carol Saleh 1 , Venkateswaran Subramaniam 1 , Annetta Seivwright 2 , Gerald Joseph Prud’homme 1,2 , George Makram Yousef 1,2 1 Department of Laboratory Medicine, and the Keenan Research Centre for Biomedical Scienceatthe Li Ka Shing Knowledge Institute 2 Department of Pathology and Laboratory Medicine, University of Toronto, M5G 1L5, Canada Correspondence: George Makram Yousef, email: // Keywords : Clear cell renal cell carcinoma / microRNA / Cancer stem cell- Tumor initiating cell / Epithelial-to-mesenchymal transition Received : January 23, 2014 Accepted : April 16, 2014 Published : April 16, 2014 Abstract Renal cell carcinoma (RCC) is an aggressive disease, with 35% chance of metastasis. The ‘ cancer stem cell’ hypothesis suggests that a subset of cancer cells possess stem cell properties and is crucial in tumor initiation, metastasis and treatment resistance. We isolated RCC spheres and showed that they exhibit cancer stem cell/ tumor initiating cell-like properties including the formation of self-renewing spheres, high tumorigenicity and the ability to differentiate to cell types of the original tumor. Spheres showed increased expression of stem cell-related transcription factors and mesenchymal markers. miRNAs were differentially expressed between RCC spheres and their parental cells. Inhibition of miR-17 accelerated the formation of RCC spheres which shared molecular characteristics with the spontaneous RCC spheres. Target prediction pointed out TGFβ pathway activation as a possible mechanism to drive RCC sphere formation. We demonstrate that miR-17 overexpression interferes with the TGFβ-EMT axis and hinders RCC sphere formation; and validated TGFBR2 as a direct and biologically relevant target during this process. Thus, a single miRNA may have an impact on the formation of highly tumorigenic cancer spheres of kidney cancer.