The MYC-SWI/SNF connection in rhabdoid tumors

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PROJECT SUMMARY Rhabdoid tumors are rare and aggressive pediatric cancers with high rates of mortality and few treatment options. Most children diagnosed with rhabdoid tumors will die within 18 months of diagnosis, often after grueling treatment regimens that involve combinations of surgery, chemotherapy, and radiation. The molecular basis of rhabdoid tumors is remarkably simple, and involves loss of a single tumor suppressor— SMARCB1—which encodes the SNF5 component of the SWI/SNF chromatin remodeler. Identification of SNF5 loss as the driver of rhabdoid tumors was a major breakthrough in understanding the disease, but raises the question of how the absence of SNF5 promotes tumorigenic programs and whether there are actionable targets for therapeutic intervention in these cancers. The premise of this project is that loss of SNF5 causes rhabdoid tumors, at least in part, by activating c-MYC, an oncoprotein transcription factor with extensive ties to cancer. Supporting this premise are preliminary data showing: (i) an extensive overlap between the primary transcriptional effects of MYC inhibition and SNF5 re-introduction in rhabdoid tumor cells, (ii) physical interactions between MYC and SWI/SNF components that are blocked by SNF5, (iii) the ability of SNF5 to separately inhibit DNA binding by MYC, (iv) MYC-dependent recruitment of a core SWI/ SNF component to chromatin in rhabdoid tumor cells, and (v) an essential role for MYC in rhabdoid tumor cell survival and transformation. Together, these data explain the recurrent presence of MYC target gene signatures in rhabdoid tumor patients, and support a model in which loss of SNF5 stimulates a productive interaction of MYC on chromatin with 'residual' SWI/SNF complexes—which in turn drives key tumorigenic transcriptional programs in these malignancies. The goal of this project is to characterize the MYC–SWI/ SNF connection in rhabdoid tumor cells, and determine its role in sculpting the rhabdoid transcriptome. Specific Aim 1 will use a combination of biochemical, genetic, and genomic approaches to define components of the MYC–SWI/SNF complex and to characterize their recruitment to sites across the rhabdoid genome. Specific Aim 2 will combine high resolution transcriptomic analyses with cell-based assays to reveal primary transcriptional events that are controlled via the MYC–SWI/SNF interaction in rhabdoid tumor cells and to decipher the underlying mechanisms. Completion of these studies will rigorously challenge the idea that MYC is a defacto driver of oncogenic transcriptional processes in these cancers. These studies will also expose whether MYC inhibitors are likely to be an effective therapeutic option in rhabdoid cancers, and will establish a paradigm for how tumor-associated mutations in SWI/SNF— which occur in 20% of all cancers—intersect with classic oncogenic pathways to drive malignancy.