Mentor Name: Jessica Tsai

Atypical teratoid rhabdoid tumors (ATRT) are extremely aggressive childhood central nervous system tumors that most often affect children age 3 and younger. The majority of ATRT cases are characterized by bi-allelic deletions in SMARCB1, while the remaining cases harbor SMARCA4 loss of function mutations. More recent transcriptomic and epigenetic data have led to the development of ATRT molecular subgrouping, however current treatment does not distinguish between these subgroups. While there have been some improvements in clinical outcomes with multimodal therapy (including surgical resection, cytotoxic chemotherapy, radiation, and high-dose chemotherapy followed by autologous stem cell transplantation), there remains significant morbidity and toxicities associated with such intensive therapy. Treatment with cytotoxic chemotherapy as well as high dose chemotherapy can result in severe toxicities including life-threatening infections, bleeding, and organ failure, which are particularly challenging in the younger age group of children affected by ATRT. Focal radiation and craniospinal radiation can have devastating neurodevelopmental effects in children under the age of 3. Exportin 1 (XPO1) is a nuclear export protein that transports nuclear proteins containing a nuclear export signal (NES) from the nucleus to the cytoplasm. Overexpression of XPO1 has been associated with poor prognosis and tumor invasion in many adult cancers. We have previously shown that XPO1 is a potent vulnerability in AT/RT cells. However, the identity of XPO1 cargo proteins is presently unknown. This project will utilize protein fractionation and mass spectrometry to identify XPO1 cargo proteins. AT/RT cells treated with XPO1 inhibitors will lead to cargo proteins remaining stuck in the nucleus. Therefore, comparing the cytoplasmic protein fraction in parental AT/RT cells to the nuclear fraction in AT/RT cells with XPO1 inhibition will provide candidate cargo proteins. We will ultimately validate these cargo proteins using co-immunoprecipitation methods. Identification of these cargo proteins will help us to understand how blocking nuclear export kills AT/RT cells.