PROJECT SUMMARY A research program will be undertaken to study SMARCB1-regulated SWI/SNF complex function in malignant rhabdoid tumors. Over the past few years, major cancer genome sequencing studies have identified frequent inactivating mutations of mammalian SWI/SNF chromatin remodeling complex in over 25% of human cancers. Despite the prevalence of SWI/SNF mutations, the contributions of these alterations to tumorigenesis remain unclear. SMARCB1, a core subunit of the complex, was the first subunit linked to cancer when it was found to be recurrently mutated in almost all cases of malignant rhabdoid tumors (RT). While studies using genetically engineered mouse models have firmly established SMARCB1 as a tumor suppressor, the epigenetic mechanism by which SMARCB1 mutation drives tumorigenesis remains elusive. The central hypothesis is that the biochemical diversity of the SWI/SNF complex composition determines its function in proper chromatin targeting to maintain discrete chromatin landscapes and transcriptional programs. Mutation of SMARCB1 leads to aberrant intra- and inter-complex protein-protein interactions that influence chromatin targeting, which consequently alters chromatin landscapes and higher-order structures, and promote an oncogenic epigenome and transcriptome. The objective is to determine the role of SMARCB1 in SWI/SNF subcomplex formation and the impact of these dynamics on chromatin targeting and higher-order chromatin structure. Our ultimate goal is to determine the fundamental epigenetic mechanism(s) by which loss of this chromatin regulatory subunit drives rhabdoid tumor development. To test this hypothesis, we will use a combination of cutting edge biochemical, molecular, and high-throughput sequencing technologies to move forward the program through the following specific aims: Aim 1, Determine SMARCB1 regulated SWI/SNF subcomplex assembly dynamics and identify SWI/SNF interactome in rhabdoid tumors; Aim 2, Determine the chromatin targeting activities of SWI/SNF subcomplexes and their relationship with other epigenetic regulators in rhabdoid tumors; Aim 3, Define higher- order chromatin structures regulated by the SWI/SNF complex in rhabdoid tumors.

PROJECT NARRATIVE Twenty five percent of human cancers have mutations in subunits of the chromatin remodeling SWI/SNF complex. This research proposal describes an innovative approach to study the tumor suppressor activity of SMARCB1, a core member of the complex, which is lost in nearly all cases of an aggressive and lethal pediatric cancer named malignant rhabdoid tumor. The long-term goals of this project are to determine both how SMARCB1 regulates the SWI/SNF complex composition and targeting, and how SMARCB1 affects higher-order chromatin structure, in order to better understand how cancers arise when the complex is mutated.