PROJECT SUMMARY
Rhabdoid tumors are one of the most aggressive and lethal cancers in pediatric oncology with overall 5-year
survival rates of ~20-25%. Loss of SMARCB1 is the primary recurrent genetic alteration found in over 90% of
cases. Recent advances have implicated SMARCB1 loss in a number of other cancers broadly referred to as
SMARCB1-deficient cancers. SMARCB1 is a critical component of the BAF chromatin remodeling complex, a
complex which controls gene transcription by positioning nucleosomes at gene regulatory regions. Targeted
localization of the BAF complex to enhancers has largely been attributed to SMARCB1, yet no domain has been
identified on SMARCB1 that is able to recognize and bind specific histone marks. Instead SMARCB1 is only able
to nonspecifically bind to nucleosomes. This raises a key question: how does the BAF complex recognize
regulatory regions such as enhancers and bind. Recent work has shown that deletion of SMARCB1 depletes an
adjacent BAF subunit, DPF2, which is able to recognize and bind histone marks associated with enhancers. Re-
expression of SMARCB1 in a SMARCB1-deficient cell line leads to a robust accumulation of DPF2. The histone
reader protein, DPF2, has previously been implicated in the recruitment of the BAF complex to regulatory
regions. Through deep mutational scanning of SMARCB1, we have identified four missense mutations in
SMARCB1 that seem to mimic an oncogenic loss of function nonsense mutation. These residues are predicted
to directly interact with DPF2, which suggests SMARCB1 mediates its tumor suppressor role at least partially
through its interaction with DPF2. Moreover, we have identified a novel tumor suppressor role of DPF2 in the
context of constitutive overexpression in two SMARCB1-deficient cancers cell lines. For this reason, we
hypothesize that depletion of DPF2 is required in SMARCB1-deficient cancers. In Aim 1, I will test the hypothesis
that reduced DPF2 association with the BAF complex is driving this observed loss of function phenotype by
assessing the phenotypic, structural, and regulatory effects of each proposed SMARCB1 mutant. In Aim 2, I will
test the hypothesis that stabilization of DPF2 may be a promising therapeutic strategy to restore transcription
normalcy despite the loss of SMARCB1. In this aim I will characterize the phenotypic, structural, and regulatory
consequences of DPF2 overexpression in SMARCB1-deficent cell lines and determine if this is occurring through
either a BAF-dependent or BAF-independent mechanism. Together these aims will provide fundamental insight
into the mechanisms through which SMARCB1 exerts its tumor suppressor function, as well as expand our
understanding of DPF2 in SMARCB1-deficient cancers as a potential therapeutic target.