Endogenous TNFα Mediates Cell Survival and Chemotherapy Resistance by Activating the PI3K/Akt Pathway in Childhood Acute Lymphoblastic Leukemia.

Expression of endogenous TNFα (enTNF) by tumor cells has been shown to confer a survival advantage and resistance to chemotherapy. Here we report that constitutive activation of the PI3K/Akt pathway is an important mechanism for cell survival and chemotherapy resistance in enTNF+ acute lymphoblastic leukemia (ALL). We analyzed two pediatric ALL cell lines, EU-1 (enTNF+) and EU-3 (enTNF-) for the regulation of Akt by enTNF in association with cell growth and sensitivity to doxorubicin. EU-1 cells constitutively expressed activated/phosphorylated Akt (p-Akt) and were resistant to doxorubicin, whereas EU-3 cells were negative for p-Akt and sensitive to this drug. Treatment of EU-3 cells with supernatant from EU-1 cultures rapidly induced expression of p-Akt. Conversely, treatment with either anti-TNFα or anti-TNF-receptor 2 (TNFR2) antibodies rapidly downregulated constitutive p-Akt in EU-1 cells, and blocked p-Akt induction in EU-3 cells cultured with EU-1 supernatant. Inhibition of p-Akt either by a PI3K inhibitor Ly294002 or by TNF siRNA suppressed EU-1 growth and sensitized these cells to doxorubicin. These results suggest that enTNF produced by EU-1 activates Akt in both EU-1 and supernatant-treated EU-3 cells by binding to cell-surface TNFR2, and that enTNF-activation of the PI3K/Akt pathway may be associated with drug-resistance in pediatric ALL.