Dissecting the cooperation of FOXR2 and ETS transcription factors in FOXR2-expressing diffuse midline gliomas

PROJECT SUMMARY Diffuse midline gliomas (DMGs) are devastating childhood brain tumors for which there are no effective therapies. While histone mutations are thought to be a critical tumor initiating event, they are insufficient for glioma formation and co-occur with somatic alterations in other pathways, including MYC and growth factor

receptor signaling. I have recently discovered that a subset of DMGs aberrantly express the forkhead transcription factor FOXR2. FOXR2 is sufficient to enhance DMG formation and also required for FOXR2- expressing DMGs. FOXR2 DNA-binding is highly enriched at E26 transformation-specific (ETS) motifs, and

FOXR2 specifically activates ETS transcriptional circuits. Moreover, FOXR2-expressing DMGs lack amplifications and genetic events in growth factor receptor pathways, suggesting functional redundancy. Indeed, phosphoproteomic evidence shows that FOXR2-expressing cells activate MAPK signaling. These findings

provide the rationale to study how aberrant FOXR2 expression cooperates with ETS transcription factors to enhance DMG formation by activating downstream pathways, including MAPK signaling. To advance our understanding of FOXR2-expressing DMGs, this proposal will pursue the following two Specific Aims: 1) Test

the hypothesis that ETS transcription factors are required for FOXR2-mediated oncogenesis and 2) Test the hypothesis that the oncogenic phenotype of FOXR2 is mediated through MAPK signaling. I am currently an Instructor in Pediatrics and a Pediatric Neuro-Oncologist at Dana-Farber Cancer Institute with 80% of my time protected for research. I am fully committed to a career as a physician-scientist, with the

goal of elucidating DMG disease mechanisms to advance patient care. The purpose of this career development award is to fill a critical gap in my training and enable me to gain specific skills in in vivo animal modeling of pediatric brain tumors and high-throughput genetic perturbation approaches. I have chosen an outstanding

mentorship team, Dr. Pratiti Bandopadhayay and Dr. Myles Brown. Dr. Bandopadhayay is an established leader in pediatric brain tumor genomics, and Dr. Brown is an international leader in epigenomics and chromatin biology with extensive experience in mentoring physician-scientists. My scientific advisory committee includes experts

reflecting key areas of my training plan: Drs. Eric Fischer (proteomics), Timothy Phoenix (murine glioma models), Keith Ligon (immunohistochemical analyses of murine models), and Kim Stegmaier (pediatric cancer genomics and high-throughput genetic perturbation assays). I will moreover collaborate with Dr. John Doench (high-

throughput genetic perturbation methods and analyses) to gain expertise. Under the mentorship of my co- mentors and the commitment of my scientific advisory committee, I will train in the stimulating environments of Dana-Farber Cancer Institute and the Broad Institute, both outstanding institutions with tremendous resources.

The K08 award offers me further mentored research time and essential career development training to ultimately emerge as an independent physician-scientist investigator in the field of Pediatric Neuro-Oncology.