Role of targeting integrin-linked kinase in suppression of invasion and metastasis through downregulation of epithelial to mesenchymal transition in renal cell carcinoma

Abstract

Renal cell carcinoma (RCC) is the most common malignancy in the kidney and advanced RCC is related to a poor prognosis. Anti-angiogenic targeted therapies inhibit the progression of RCC, but have no or negative effects on invasion and metastasis of tumor cells. Integrin-linked kinase (ILK) is a serine/threonine kinase implicated in the regulation of cell growth and survival, cell cycle progression, epithelial-mesenchymal transition (EMT), invasion and migration, and angiogenesis. However, the role of ILK in RCC has not been evaluated. Here, we investigated the role of ILK on cancer progression and metastasis and the therapeutic potential of ILK inhibition in RCC. Our investigation revealed that ILK is expressed at a low level in normal cells (HK-2) and low-stage RCC cells (UMRC-6), but highly expressed in advanced and metastatic cells (UMRC-3 and Caki-1). Caki-1, a metastatic RCC cell line showed higher expression of molecular EMT markers including Snail and Zeb1, but decreased activity of glycogen synthase kinase 3 beta (GSK3β). Knockdown of ILK using small interference (si)-ILK inhibited tumor proliferation, but the inhibition rate was minimal and cell cycle progression was not significantly affected. However, ILK knockdown suppressed the formation of stress fibers and focal adhesions in UMRC-3 and Caki-1 cells, and impeded phenotypic EMT markers, including cell migration and invasion, in Caki-1 and UMRC-3 cells. Finally, in vivo knockdown of ILK suppressed the progression, invasion and metastasis of primary RCC in nude mice. Immunohistochemical studies showed that Snail, Zeb1, vimentin, and E-cadherin were downregulated upon ILK knockdown. Critically, in advanced RCC, ILK is highly expressed and its expression is related to EMT-related proteins. Thus, ILK is essential for invasion and metastasis in RCC and regulates vimentin expression by regulating EMT-related transcription factors Snail and Zeb1. These results suggest the potential of ILK inhibition as an anti-metastasis therapy for advanced RCC.