RXRA sumoylation enhances PML/RARA-mediated immortalization. (A) Sumoylation profile of transfected RXRA WT or K113R in H1299 cells stably expressing HIS-SUMO1 and expressing (+) or not (−) PML/RARA. (B) Analysis of rarb gene activation by RA (1 µM) in MEFs expressing RXRA or RXRA K113R in the presence (Rars^−/− MEFs, right panel) or absence (MEFs, left panel) of PML/RARA. Error bars represent standard deviations of 3 independent biological replicates. Significance of observed differences was evaluated using Student t test. *P < .05. (C) Progenitors transduced with murine RXRA WT or K113R and PML/RARA, RARA, or MLL-ENL were analyzed for clonogenicity. Error bars represent standard deviations of 3 independent biological replicates. Significance of observed differences was evaluated using Student t test. *P < .05; **P < .01; ***P < .001. (D) Progenitors transduced with murine RXRA WT or K113R and PML/RARA, RARA, or MLL-ENL were analyzed for morphology (bottom bar, 10 µm; MGG stain). (E) Protein expression by western blot (black dividing lines show grouping of images from different parts of the same exposed film). (F) Cos-7 cells coexpressing RARA and RXRA or RXRA K113R were treated with cycloheximide (0.1 mg/mL) and RA (1 µM) for the indicated time, and the half-life of RXRA and RARA proteins was analyzed by western blot.