Figure 1. Schematic of the effects of GSK-3β inactivation on MCF-7 cell sensitivity to doxorubicin or tamoxifen. Arrows indicate activating events, whereas perpendicular lines indicate inhibitory events. At present, it is not clear how doxorubicin could dephosphorylate GSK-3β and activate Akt at the same time. Doxorubicin could either inhibit other protein kinases, targeting Ser9 p-GSK-3β, or stimulate protein phosphatases.