ATRA resistance conferred by a clustered subset of hotspot PML::RARA mutations enhancing basal repression rather than precluding transactivation.

Most acute promyelocytic leukemia (APL), driven by the PML::RARA fusion, are now cured with targeted therapies combining all-trans retinoic acid (ATRA) and arsenic trioxide. Some patients treated with earlier ATRA/chemotherapy regimen developed resistance associated with mutations that most often preclude PML::RARA ATRA-binding. Here, we characterized a subset of clustered mutations associated with ATRA-resistance, but not predicted to affect ATRA binding. Most mutants indeed retained full ligand responsiveness, but displayed a basal super-repressive phenotype which did not result from an increased affinity for known corepressors such as NCoR and SMRT. Our findings suggest these mutations are gain-of-function associated with enhanced interactions with unidentified RARA partners with repressive ability. Similar to ATRA-resistant PLZF::RARA variants, these observations stress the role of persistent transcriptional repression of some retinoic acid target genes in acquired ATRA-resistance.