PTPA and B-cell chronic lymphocytic leukemia: As a further measure of PP2A activity, we observed dose-dependent AKT dephosphorylation, a well-documented PP2A substrate, in DT-061–treated CLL cells, which was effectively rescued by pretreatment with the serine/threonine phosphatase inhibitor calyculin A (Supplemental Figure 4, B and C).