Project Summary: Pediatric low-grade gliomas (pLGGs) typically harbor only a single oncogenic driver mutation. In most tumors this driver mutation is a fusion between the N-terminus of KIAA1549 and the C-terminus of BRAF. Many patients with these driver mutations respond to BRAF inhibitors, but several challenges remain in extending clinical benefit to all patients. One challenge is that there is often severe toxicity associated with these treatments which necessitates cessation of treatment. These clinical observations highlight a clear need to develop new therapeutic strategies to treat pLGG. We identified the two core members of the POMT complex (POMT1 and POMT2) as being selectively essential for the survival of KIAA1549:BRAF-dependent cells. The POMT complex is necessary for O-mannosylation of secreted and transmembrane proteins, which is striking because KIAA1549 is reported to be highly mannosylated. It was originally hypothesized that the KIAA1549:BRAF fusion activates BRAF by truncating its N-terminal negative regulatory domains, but my preliminary data suggests that the KIAA1549 portion of the fusion is also necessary for activating BRAF. The primary goals of this proposal are to more broadly understand how the KIAA1549:BRAF fusion is activated, and to understand why the POMT complex is a selective dependency in KIAA1549:BRAF-dependent cells. In Aim 1 I will test the hypothesis that POMT enzymatic activity is necessary for the survival of KIAA1549:BRAF rearranged pLGG. In Aim 2 I will test the hypothesis that O-mannosylation of KIAA1549:BRAF is necessary for oncogenic signaling. And in Aim 3 I will test the hypothesis that cleavage of KIAA1549:BRAF by Furin is necessary for RAF activation. During this proposal I will also engage in a range of activities designed to enhance my scientific training. I will attend and present at multiple national and international conferences and will participate in retreats and networking events with other pediatric oncology groups. My ultimate career goal is to establish my own independent research laboratory focused on pediatric neurooncology. The training I receive through this fellowship is a necessary step towards this goal.

Project Narrative The most frequent genomic alteration in pediatric low-grade gliomas is a rearrangement that creates a fusion between the oncogene BRAF and the uncharacterized protein KIAA1549. Inhibitors which block the function of this fusion are effective but cause significant toxicity and require continuous dosing throughout childhood. The goal of this project is to define new therapeutic targets in KIAA1549-BRAF mutant pLGGs, with a focus on characterizing how the POMT complex regulates KIAA1549-BRAF activity.