Prognostic impacts of the three AKT isoforms in acute myeloid leukemia. Is AKT3 the bad AKTOR?

The PI3K-AKT-mTOR pathway lies at the confluence of signaling pathways in which various components are subjected to activating genetic alterations in acute myeloid leukemia (AML), thus contributing to oncogenesis. Three AKT isoforms exist in humans. However, whether one isoform predominates in AML remains unknown. This study reveals that AKT3 behaves very distinctly than AKT1 or AKT2 in both normal myeloid differentiation and AML. During normal differentiation, AKT3 is preferentially expressed in hematopoietic stem cells whilst AKT1 becomes preferentially expressed as cells differentiate into granulocytes or monocytes. AKT2 expression remains unchanged. In AML, AKT3 expression varies widely among patient samples and is counterintuitively correlated to the expression of monocyte markers. Furthermore, a low level of AKT3 expression is strongly correlated to genetic alterations associated with a better outcome ( NPM1 mutations and RUNX1 - RUNX1T1 translocation), whilst a high level is correlated to a genetic alteration associated to a bad outcome ( RUNX1 mutations). Neither AKT1 nor AKT2 expression associates with AML mutations or translocations. Consistently, a high AKT3 expression level appears as a very strong predictor of poor survival. Curiously, although modestly varying among AML samples, a high AKT1 expression shows in contrast as a strong predictor of a better patient outcome. These data suggest that AKT3 and AKT1 expressions have strong, yet opposite, prognostic values.