Project description:The drug efflux pump ABCB1 is a key driver of chemoresistance, and high expression predicts for treatment failure in acute myeloid leukemia (AML). We show that both acute and chronic exposure of leukemia cells to daunorubicin activates an integrated stress response-like transcriptional program to induce ABCB1 through remodeling and dynamic activation of an ATF4-bound, stress-responsive enhancer. In primary human AML, stress-responsive ABCB1 enhancers are accessible and acetylated, and exposure of fresh blast cells to daunorubicin induces ABCB1 in a dose-dependent manner. Dynamic induction of ABCB1 by diverse stressors, including chemotherapy, facilitates escape of leukemia cells from targeted third-generation ABCB1 inhibition. Stress-induced up regulation of ABCB1 is mitigated by combined use of pharmacologic inhibitors U0126 and ISRIB, which inhibit stress signaling.
Project description:The bromodomain and extraterminal (BET) protein BRD4 is a therapeutic target in acute myeloid leukemia (AML). Here, we demonstrate that the AML maintenance function of BRD4 requires its interaction with NSD3, which belongs to a subfamily of H3K36 methyltransferases. Unexpectedly, AML cells were found to only require a short isoform of NSD3 that lacks the methyltransferase domain. We show that NSD3-short is an adaptor protein that sustains leukemia by linking BRD4 to the CHD8 chromatin remodeler, by using a PWWP chromatin reader module, and by employing an acidic transactivation domain. Genetic targeting of NSD3 or CHD8 mimics the phenotypic and transcriptional effects of BRD4 inhibition. Furthermore, BRD4, NSD3, and CHD8 colocalize across the AML genome, and each is released from super-enhancer regions upon chemical inhibition of BET bromodomains. These findings suggest that BET inhibitors exert therapeutic effects in leukemia by evicting BRD4-NSD3-CHD8 complexes from chromatin to suppress transcription. ChIP-Seq for regulatory factors of BRD4, NSD3, CHD8 and histone modification H3K36me2 in MLL-AF9 transformed acute myeloid leukemia cells (RN2)