Nuclear exclusion of the forkhead transcription factor FOXO3a by protein kinase Akt contributes to cell survival. We investigated the pathological relationship between phosphoylated-Akt (Akt-p) and FOXO3a in primary tumors. Surprisingly, FOXO3a was found to be excluded from the nuclei of some tumors lacking Akt-p, suggesting an Akt-independent mechanism of regulating FOXO3a localization. We provide evidence for such a mechanism by showing that IkappaB kinase (IKK) physically interacts with, phosphorylates, and inhibits FOXO3a independent of Akt and causes proteolysis of FOXO3a via the Ub-dependent proteasome pathway. Cytoplasmic FOXO3a correlates with expression of IKKbeta or Akt-p in many tumors and associates with poor survival in breast cancer. Further, constitutive expression of IKKbeta promotes cell proliferation and tumorigenesis that can be overridden by FOXO3a. These results suggest the negative regulation of FOXO factors by IKK as a key mechanism for promoting cell growth and tumorigenesis.

B-cell leukemia/lymphoma 2 (BCL-2) prevents commitment to programmed cell death at the mitochondrion. It remains a challenge to identify those tumors that are best treated by inhibition of BCL-2. Here we demonstrate that acute myeloid leukemia (AML) cell lines, primary patient samples, and murine primary xenografts are very sensitive to treatment with the selective BCL-2 antagonist ABT-199. In primary patient cells, the median IC50 was approximately 10 nM, and cell death occurred within 2 h. Our ex vivo sensitivity results compare favorably with those observed for chronic lymphocytic leukemia (CLL), a disease for which ABT-199 has demonstrated consistent activity in clinical trials. Moreover, mitochondrial studies using BH3 profiling demonstrate activity at the mitochondrion that correlates well with cytotoxicity, supporting an on target mitochondrial mechanism of action. Our protein and BH3 profiling studies provide promising tools that can be tested as predictive biomarkers in any clinical trial of ABT-199 in AML.