Project description:MYC is a major oncogenic driver of Multiple Myeloma (MM) and yet almost no therapeutic agents exist that target MYC in MM. Here we report that the let-7 biogenesis inhibitor LIN28B correlates with MYC expression in MM and is associated with adverse outcome. We also demonstrate that the LIN28B/let-7 axis modulates the expression of MYC, itself a let-7 target. Further, perturbation of the axis regulates the proliferation of MM cells in vivo in a xenograft tumor model. RNA sequencing and gene set enrichment analyses of CRISPR-engineered cells further suggest that the LIN28/let-7 axis regulates MYC and cell cycle pathways in MM. We provide proof-of-principle for therapeutic regulation of MYC through let-7 with an LNA-GapmeR containing a let-7b mimic in vivo, demonstrating that high levels of let-7 expression repress tumor growth by regulating MYC expression. These findings reveal a novel mechanism of therapeutic targeting of MYC through the LIN28B/let-7 axis in MM that may impact other MYC dependent cancers as well.
Project description:Deubiquitylases (DUBs) remove ubiquitin from proteins. In the context of cancer, their inhibition can induce the degradation of oncoproteins, that may otherwise be “undruggable”. Multiple myeloma (MM) is the second most common hematological malignancy with poor outcome and high sensitivity towards ubiquitin-proteasome-system (UPS) inhibitory therapies. However, the role of DUBs in MM pathophysiology and therapy has remained elusive. Starting from genetic screening for DUB dependencies in MM, we here identify OTUD6B as a central vulnerability in MM that drives the G1/S cell cycle transition by means of deubiquitylating and stabilizing LIN28B subsequent to LIN28B phosphorylation. LIN28B regulates miRNA biogenesis and exerts high expression in embryonic stem cells that becomes re-established in certain tumors, including MM. Binding of LIN28B at G1/S activates OTUD6B, which otherwise remains in a catalytically inactive state. As a consequence, stabilized LIN28B drives MYC expression via inhibition of let7 microRNAs, which in turn allows for a rapid transition of MM cells from G1 to S phase. Analyses of primary MM patient samples reveal a positive correlation of OTUDB6B expression with poor outcome, high MYC expression and MYC target gene induction, suggesting that high MYC levels in MM result from an activation of the OTUD6B-LIN28B nexus. Together, we here specify phosphorylation and cell cycle-dependent substrate binding as a means by which OTUD6B becomes activated to drive the G1/S transition via the LIN28B-MYC axis and nominate OTUD6B and LIN28B as actionable vulnerabilities in MM.
Project description:Here we report the use of high-throughput sequencing technologies (RNA-seq, ChIP-seq) to identify the molecular programme of PBX1 and FOXM1 in multiple myeloma cells (MM1S, U266 cell lines). We performed Chromatin Immunoprecipitation followed by sequencing (ChIP-seq) against PBX1 in MM1S and U266 cells (n=2). In addition, we identifed the transcriptome of PBX1-depleted and FOXM1-depleted myeloma cells 3 days after transduction with shRNA-expressing lentiviral vectors. Molecular characterization revealed PBX1 as a novel epigenetic regulator of myeloma cell survival and proliferation. PBX1 directly and unilaterally controls the FOXM1 transcriptional programme and, together,they regulate the high-risk transcriptional signature of chr1q-amplified cells. Pharmacological inhibition of the unified PBX1-FOXM1 axis with thiostrepton showed selectivity against chr1q-amplified MM. Altogether, these data reveal PBX1-FOXM1 axis as a novel therapeutic avenue against chr1q-amplified MM.
Project description:SPO11-promoted DNA double-strand breaks (DSBs) formation is a crucial step for meiotic recombination, and it is indispensable to detect the broken DNA ends accurately for dissecting the molecular mechanisms behind. Here, we report a novel technique, named DEtail-seq (DNA End tailing followed by sequencing), that can directly and quantitatively capture the meiotic DSB 3’ overhang hotspots at single-nucleotide resolution.