U937 leukemic cells expressing PML/RARα I410T show ATRA binding and transcriptional activity similar to that of NB4 APL cells. (A) Comparison of specific ATRA-binding profiles of the PML/RARα mutant I410T overexpressed in U937 cells. Nuclear extracts of U937-transfected cells were subjected to Western blot analysis for the 110-kDa PML/RARα wild-type or mutant I410T (left-pointing arrow). (B) Comparison of the ligand-dependent transcriptional activity, on a DR5-tk-CAT, of overexpressed PML/RARα wild-type and mutant I410T into U937 cells. Assays were performed in triplicate. Bars represent standard deviation of the mean.