CSIG-26. NF2/MERLIN DRIVES MENINGIOMA APOPTOSIS AND SUCEPTIBILITY TO CYTOTOXIC THERAPY

• Published in: Neuro-oncology (Charlottesville, Va.) Vol. 23; no. Supplement_6; p. vi39
• Main Authors: Eaton, Charlotte, Choudhury, Abrar, Casey-Clyde, Timothy, Swaney, Danielle, Krogan, Nevan, Raleigh, David
• Format: Journal Article
• Language: English
• Published: US Oxford University Press 12.11.2021
• ISSN: 1522-8517; 1523-5866
• DOI: 10.1093/neuonc/noab196.152

Abstract BACKGROUND Alterations in NF2 underlie meningioma tumorigenesis, but tumor suppressor functions of the NF2 gene product, Merlin, are incompletely understood in meningiomas. Here we integrate proteomic proximity-labelling mass spectrometry with CRISPR interference (CRISPRi), RNA sequencing, and biochemical approaches to discover Merlin drives meningioma apoptosis and susceptibility to cytotoxic therapy. METHODS RNA sequencing was performed on triplicate M10G meningioma cells stably expressing CRISPRi machinery and either non-targeting control sgRNAs, sgRNAs suppressing NF2, or sgRNAs suppressing NF2 with Merlin rescue. QPCR in IOMM-Lee and MSC1 meningioma cells expressing non-targeting control shRNAs or shRNAs suppressing NF2 was used for orthogonal validation in vitro. RNA sequencing of euploid meningiomas (n=52) or meningiomas with loss of NF2 as the only copy number variant (n=28) was used for orthogonal validation in vivo. Merlin interactors in meningioma cells were identified using APEX proteomic proximity-labelling mass spectrometry. Mechanistic and functional studies were performed using biochemical, molecular, and cell biology approaches in meningioma cells and CH-157MN meningioma xenografts treated with cytotoxic chemotherapy or ionizing radiation. RESULTS Merlin suppression in meningioma cells and xenografts inhibited pro-apoptotic interferon regulatory factor (IRF) target genes and attenuated meningioma apoptosis. Merlin suppression did not alter IRF stability or subcellular localization in meningioma cells, and proteomic proximity-labelling mass spectrometry revealed a novel interaction between wildtype Merlin and ARHGAP35, a DNA binding factor that inhibits glucocorticoid receptor expression (NR3C1). NR3C1 inhibits IRF activity to prevent apoptosis, and Merlin suppression in meningioma cells induced NR3C1expression, which was inhibited by Merlin rescue. Further, NR3C1 suppression rescued meningioma cell apoptosis in the absence of Merlin, and NR3C1 expression was increased in human meningiomas with loss of NF2 compared to euploid meningiomas. CONCLUSIONS These data shed light on a novel pro-apoptotic tumor suppressor function of Merlin regulating glucocorticoid signalling and susceptibility to cytotoxic therapy in meningiomas.