Resistance to ATO-mediated GC sensitization by XIAP overexpression requires the XIAP-S87 phosphorylation site. (A) Response to increasing concentrations of DEX after 72-hour incubation in combination with 0.25 μM ATO, after transient transfection of different XIAP constructs as indicated and described in “Patients, materials, and methods.” Triplicate results of the MTT assay are shown as mean plus or minus SD. (B) Western blot with specific anti-XIAP antibody (top panel) and an anti-GFP antibody (bottom panel).