A better understanding of dysregulated signaling pathways in
cancer cells may suggest novel strategies to prevent
tumor development and/or progression. Here we show that Jurkat and CCRF-CEM human T-
leukemia cell lines were more sensitive than normal human T cells to the cytotoxic effect of inhibiting
protein phosphatase 2A (PP2A). Inhibition of PP2A by
okadaic acid (OA) caused T-
leukemia cells to die by apoptosis, as indicated by DNA fragmentation,
caspase-3 activation, loss of mitochondrial membrane potential (DeltaPsi(m)), and changes in nuclear morphology that were consistent with apoptosis. PP2A might therefore be a useful intracellular target for the treatment of T cell-derived
leukemias. We also observed that
reactive oxygen species (ROS) were generated in response to PP2A inhibition in T-
leukemia cells. However, loss of DeltaPsi(m) that resulted from PP2A inhibition was not prevented by exogenous
antioxidants (
glutathione and N-acetyl-
cysteine), indicating that OA-induced changes in mitochondrial membrane permeability were not a consequence of ROS production. Moreover, exogenous
antioxidants protected CCRF-CEM T-
leukemia cells from apoptosis caused by PP2A inhibition but failed to prevent OA-induced apoptosis in Jurkat T-
leukemia cells, indicating a differential role for ROS in apoptosis caused by PP2A inhibition in two different human T-
leukemia cell lines.