Chip of BRD4 in Neurofibromatosis type 2

Background: Neurofibromatosis type 2 (NF2) is an autosomal dominant genetic disease characterized by the development of multiple Schwannomas, usually occurring on both VIIIth (vestibular) cranial nerves. Bromodomain and extra-terminal domain (BET) proteins regulate gene transcription and their activity is required in a variety of cancers including malignant peripheral nerve sheath tumors (MPNST). The use of BET inhibitors as a therapeutic option to treat NF2 schwannomas has not been explored and is the focus of this study. Methods: A panel of normal and NF2-null Schwann cell and schwannoma cell lines were used to characterize the impact of the BET inhibitor JQ1 in vitro and in vivo. The mechanism of action was explored by chromatin immunoprecipitation (ChIP) of the BET BRD4, phospho-kinase arrays and immunohistochemistry of BRD4 in human vestibular schwannomas. Results: JQ1 inhibited the proliferation of NF2-null schwannoma and Schwann cell lines in vitro and in vivo. Further, loss of NF2 by CRISPR deletion or siRNA knockdown increased the sensitivity of cells to JQ1. Knock-down experiments identified BRD4 as the BET family member mediating the majority of JQ1 effects on cell proliferation. Immunohistochemistry demonstrated elevated levels of BRD4 protein in human vestibular schwannomas. BRD4 ChIP experiments identified the small G-protein Rac1 and PI3K signaling pathways as sensitive to JQ1. Conclusions: NF2 deficient Schwann cell and schwannoma cells are sensitive to BET inhibition, primarily mediated by BRD4, which is overexpressed in human vestibular schwannomas. BRD4 regulates Rac/Ras and PI3K signaling pathways and inhibition of these pathways by JQ1 impedes NF2 Schwannoma growth. These findings implicate BET inhibition as a therapeutic option for NF2-deficient schwannomas. 2 biological replicates from Jq1-treated or mock (DMSO)-treated human NF2 cell lines