Resistance to the mTOR Inhibitor Temsirolimus Alters Adhesion and Migration Behavior of Renal Cell Carcinoma Cells through an Integrin [alpha]5- and Integrin [beta]3-Dependent Mechanism

• Published in: Neoplasia (New York, N.Y.) N.Y.), 2014-04, Vol.16 (4), p.291-300
• Main Authors: Juenael, Eva, Makarevic, Jasmina, Reiter, Michael, Mani, Jens, Tsaur, Igor, Bartsch, Georg, Haferkamp, Axel, Blaheta, Roman A
• Format: Article
• Language: English
• ISSN: 1522-8002
• DOI: 10.1016/j.neo.2014.03.011

Inhibitors of the mammalian target of rapamycin (mTOR) have improved the treatment of renal cell carcinoma (RCC). However, chronic drug exposure may trigger resistance, limiting the utility of these agents. The metastatic behavior of RCC cells, susceptible (RCC super(par)) or resistant (RCC super(res)) to the mTOR inhibitor temsirolimus, was investigated. Adhesion to vascular endothelium or immobilized collagen and fibronectin was quantified. Chemotactic motility was evaluated with a modified Boyden chamber assay. Integrin a and [beta] subtype receptors were analyzed by flow cytometry and Western blot analysis. The physiological relevance of the integrins was then determined by blocking studies and small interfering RNA knockdown. Adhesion to endothelial cells and to fibronectin (not to collagen) and chemotaxis were enhanced in RCC super(res) compared to RCC super(par). RCC super(res) detached from fibronectin and motile activity further increased under retreatment with low-dosed temsirolimus. [alpha]5 integrin was diminished inside the cell and at the cell surface, whereas the [beta]3 subtype was reduced intracellularly but elevated at the plasma membrane. In RCC super(par), blocking [alpha]5 surface receptors enhanced RCC-collagen but reduced RCC-fibronectin interaction, whereas the opposite was true for RCC super(res). Chemotaxis of RCC super(par) but not of RCC super(res) was strongly diminished by the [alpha]5 antibody. Blocking [beta]3 significantly lowered chemotaxis with stronger effects on RCC super(res), compared to RCC super(par). Importantly, [beta]3 knockdown reduced chemotaxis of RCC super(par) but upregulated the motile behavior of RCC super(res). Temsirolimus resistance is characterized by quantitative alterations of integrin [alpha]5 and [beta]3 expression, coupled to functional changes of the integrin molecules, and forces a switch from RCC adhesion to RCC migration.