| Purpose: Ewing sarcoma family tumors (ESFT) are highly aggressive pediatric and young adult stem cell tumors for which prognostic biomarkers and novel treatments are needed. New treatments targeting the IGF-1R signaling pathway show promise, but may not be effective in treating all patients. We have assessed the potential clinical significance of BMI-1 expression level on treatments utilizing IGF-1R inhibition.;Experimental Design: BMI-1-positive and -negative ESFT cell lines were identified using PCR, Q-RT-PCR, and western blot analysis. Sensitivity to IGF1-R inhibition was determined using MTS [3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium] assays. Performing gain and loss of function studies assessed the role of BMI-1 on IGF-1R inhibition. The effect of IGF-1 inhibition on cell viability was evaluated by PARP cleavage western blots. Cooperation between BMI-1 and IGF-1 was assessed by performing immunoblotting to detect Akt phosphorylation.;Results: BMI-1 expression is negatively correlated with IGF-1R axis signaling in ESFT. Significantly, although BMI-1-positive cell lines are more sensitive to IGF-1R inhibition than BMI-1-negative cells, overexpressing BMI-1 decreased this sensitivity, while knocking down BMI-1 expression increased the effects of IGF-1R inhibition. PARP cleavage western blots showed that the likely mechanism of decreased viability in cell lines treated with IGF-1R inhibition is apoptosis. Consistent with these data, we have shown that BMI-1 and IGF-1 cooperate to promote Akt phosphorylation.;Conclusion: BMI-1 and IGF-1 signaling cooperate to promote ESFT survival and tumorigenesis through activation of the PI3K/Akt survival pathway. |
