Menin and Ewing Sarcoma Metastasis

About This Grant

Ewing sarcoma (EwS) is an aggressive bone tumor that is driven by the oncogenic fusion transcription factor (TF) EWS::FLI1. Despite a high rate of treatment response, a quarter of patients with localized tumors and almost all patients with metastatic disease relapse at distant sites months or years after entering clinical remission. Thus, subclinical disseminated tumor cells (DTCs) are a major source of recurrence and novel treatment strategies are needed to prevent outgrowth of these residual cells into macroscopic disease. The transcriptional regulator and scaffolding protein menin is highly constitutively expressed by EwS, and our preliminary studies have established that depletion of menin from EwS tumor cells inhibits their capacity to successfully colonize distant sites. Our data also indicate that this is due to a reliance on menin to maintain tumor stemness and transcriptionally regulate cell plasticity downstream of TGFβ. The best studied function of menin in transcriptional regulation is as a binding partner of MLL, where it enables epigenetic activation of gene promoters through deposition of H3K4me3. Interactions between menin and MLL-fusion proteins are required for leukemogenesis in MLL-rearranged leukemia and inhibitors of these interactions are showing promise in clinical trials. Unlike in leukemia, our data suggest that in EwS, menin-mediated control of stemness and cell state is achieved, in part, independently of MLL and H3K4me3 and is instead dependent on menin interactions with other TFs at intragenic and intergenic enhancers. Prior studies from our group demonstrated that TGFβ induces EwS cells to activate gene programs that promote acquisition of more mesenchymal states. Significantly, our preliminary data implicate menin in moderating the TGFβ -dependent transcriptional response. It is the goal of this proposal to test the innovative hypothesis that menin is a master regulator of EwS cell stemness, plasticity, and TGFβ - induced cell state transitions. We will also investigate if menin inhibition impedes colonization of EwS DTCs by inducing tumor cell dormancy. We will use a combination of dTag protein degrader technology, transcriptomic and epigenomic profiling, and in vivo studies of EwS colonization to determine: (i) if menin promotes tumor stemness by amplifying transcription of SOX2 and MYC target genes; (ii) how menin regulates TGFβ -dependent cell plasticity; and (iii) if high menin activity prevents EwS cells from entering a dormant state in metastatic niches. Together these studies will define the molecular mechanisms by which menin promotes EwS metastasis. Elucidation of MLL-dependent and -independent functions will illuminate if and how menin:MLL interaction inhibitors could be immediately repurposed, or if menin could be otherwise targeted to benefit patients who are at risk of metastatic relapse.