The Insulin-Like Growth Factor I Receptor Is Required for Akt Activation and Suppression of Anoikis in Cells Transformed by the ETV6-NTRK3 Chimeric Tyrosine Kinase

Abstract

Signaling through the insulin-like growth factor I receptor (IGF-IR) axis is essential for transformation by many dominantly acting oncoproteins. However, the mechanism by which IGF-IR contributes to oncogenesis remains unknown. To examine this, we compared transformation properties of the oncogenic ETV6-NTRK3 (EN) chimeric tyrosine kinase in IGF-IR-null R⁻ mouse embryo fibroblasts with R⁻ cells engineered to reexpress IGF-IR (R⁺ cells). We previously showed that R⁻ cells expressing EN (R⁻ EN cells) are resistant to transformation but that transformation is restored in R⁺ cells. We now show that while R⁻ EN cells have intact Ras-extracellular signal-regulated kinase signaling and cell cycle progression, they are defective in phosphatidylinositol-3-kinase (PI3K)-Akt activation and undergo detachment-induced apoptosis (anoikis) under anchorage-independent conditions. In contrast, R⁺ cells expressing EN (R⁺ EN cells) suppress anoikis and are fully transformed. The requirement for IGF-IR in R⁻ EN cells is overcome by ectopic expression of either activated Akt or a membrane-targeted form of EN. Moreover, compared to R⁻ EN cells, R⁺ EN cells show a dramatic increase in membrane localization of insulin receptor substrate 1 (IRS-1) in association with EN. Since EN is known to bind IRS-1 as an adaptor protein, our findings suggest that IGF-IR may function to localize EN/IRS-1 complexes to cell membranes, in turn facilitating PI3K-Akt activation and suppression of anoikis.

We thank Renato Baserga for the R⁻ cells and DNA constructs, Jill Kucab and Joan Mathers for technical advisement, and Cristina Tognon, Markus Warmuth, Michael Cox, and Sandra Dunn for helpful discussions.

This work was supported by funds from the Canadian Institutes of Health Research (to P.H.B.S.) and the Johal Program in Pediatric Oncology Basic and Translational Research. M.J.M. was funded by a Canadian Institutes of Health Research doctoral award.