Project Summary Large-scale cancer genome sequencing projects have highlighted the frequency of mutation in chromatin modifiers in cancer. Mutations in genes encoding the members of the SWI/SNF chromatin remodeling complex have been identified in close to 25% of all cancers. Thus, understanding the mechanisms by which SWI/SNF modulates gene expression is of critical importance. In normal cells, the activity of SWI/SNF in transcriptional activation is balanced by the repressive Polycomb complex, and in situations where SWI/SNF is mutated, Polycomb gains influence. Within the Roberts lab, we make use of a genomically simple but highly lethal pediatric cancer, rhabdoid tumor, that lacks both copies of SMARCB1, a core component of 2 out of the 3 SWI/SNF remodeling complexes. These rhabdoid cells depend on the activity of a third SWI/SNF remodeling complex, which lacks SMARCB1. To gain mechanistic insight into the interplay between SWI/SNF and Polycomb, in conjunction with the Pediatric Dependency Project which my mentor initiated with colleagues in Boston, we searched for genetic vulnerabilities specific to rhabdoid tumor cells. We performed CRISPR-Cas9 screening of 16 rhabdoid tumor (RT) cell lines compared with over 800 other cancer cell lines and identified a gene whose loss preferentially causes loss of viability of RT cells. We have independently validated the importance of this gene for RT cell viability, and our preliminary studies show that the encoded protein represses Polycomb function. We therefore hypothesize that loss of this protein further disrupts the SWI/SNF-Polycomb balance leading to repression of genes whose transcription is required for RT cell growth. Additionally, this protein is known to regulate important signaling pathways, and its loss may further dysregulate transcription through their disruption. Elucidation of the function of this protein will provide novel insights into chromatin-mediated control of transcription, the interplay between SWI/SNF and Polycomb which is disrupted in cancer, and importantly may link these important signal transduction pathways with SWI/SNF and Polycomb-regulated transcription. Additionally, through the study of this vulnerability, we will gain mechanistic insights that will contribute to the development of new therapies. Through this training award, I will extend my expertise in the study of signaling pathways to delve into the nucleus and will use molecular and genome-wide approaches to assess the regulation of chromatin. I will be guided in this journey by my outstanding mentor Dr. Charles Roberts, who has a fantastic record of accomplishment of mentoring trainees, and who has far exceeded my expectations. Through his leadership and the commitment of the Academic Programs Office to postdoc development, and with my access to the outstanding resources at St. Jude, I am confident that my postdoctoral training will equip me with all the tools I need to launch a successful independent research c...