Figure 3.

Expression of a catalytically inactive form of PP5 (PP5^MT) inhibits ATM kinase activity. (A) A mutant form of PP5 was generated by deleting residues 315-419 of the catalytic domain. (B) Overexpression of PP5^MT attenuates ATM kinase activity. After infection by recombinant adenoviruses, A549 cells were exposed to IR (20 Gy) and then incubated for 30 min. ATM immune complex kinase assays were performed with 1 μg of GST-p53(1-70) as the substrate. Cell lysates were immunoblotted as indicated. IR treatment led to an increased level of ATM kinase activity in control cells or PP5^WT/PP5^MT-expressing cells by 2.9-, 2.1-, and 0.8-fold, respectively. Consistent results were obtained among three independent experiments.