Meningioma-Induced Hyperostosis Is Associated with TRAF7 Gain-of-Function Missense Mutation in Primary Patient-Derived Meningioma Cells

Introduction: Meningiomas are among the only tumors that can form lamellar, hyperostotic bone in the tumor microenvironment. Mechanisms underlying meningioma-induced hyperostosis are incompletely understood, but correlative genomic studies of human samples suggest that TRAF7 missense mutations may promote bone formation in the meningioma microenvironment. Here we use functional approaches in patient-derived meningioma cells and patient-derived osteoblasts to shed light on biochemical mechanisms driving meningioma-induced hyperostosis.

Methods: Primary meningioma cell cultures were developed from regionally distinct intraosseous (IO) or intradural (ID) samples from a hyperostotic sphenoid wing meningioma, CNS WHO grade 1, which was found to encode a TRAF7 K615E missense mutation on targeted next-generation DNA sequencing. The expression of osteoblast differentiation transcription factors such as RunX2 and Osterix (Osx) or osteoblastic markers such as Osteocalcin and Alkaline phosphatase (ALPL) were evaluated in patient-derived cell cultures using QPCR and immunofluorescence. Calcium deposition after in vitro differentiation ± siRNA pertubation s was evaluated using Alzarin Red staining. Results from IO and ID patient-derived cultures were compared to results from patient-derived osteoblasts that were developed from a normal sphenoid wing (OB) or patient-derived M10G meningioma cells that were developed from a nonhyperostotic meningioma. TRAF7 and TRAF7 with K615E missense mutation were cloned into an expression vector (pcDNA3) and tested in primary cell cultures for protein stability, dimerization, localization, and protein-protein interaction.

Results: IO and ID patient-derived meningioma cells were enriched in expression of SSTR2A, a sensitive and specific meningioma marker that was not expressed by OB cells. IO cells were also enriched in expression of RunX2, Osx, Osteocalcin, and ALPL compared to ID cells. M10G and ID meningioma cells did not deposit calcium in vitro. IO cells deposited more calcium in vitro than OB cells, but IO cell calcium deposition was reversed by TRAF7 K615E knockdown compared to nontargeted control siRNAs. TRAF7 and TRAF7 with K615E missense mutation both dimerized and bound to MEKK3, a known modulator of bone production, suggesting that TRAF7 missense mutations may contribute to meningioma-induced hyperostosis through noncanonical pathways.

Conclusions: Here we show primary patient-derived cell cultures from a hyperostotic sphenoid wing meningioma express markers of early and late osteoblast differentiation and can deposit calcium in vitro. To determine if the TRAF7 missense mutation identified in this tumor contributed to hyperostosis, we suppressed TRAF7 in vitro and reversed the calcium deposition phenotype of our patient-derived meningioma cells. These results suggest hyperostotic transdifferentiation of meningioma cells into osteoblast-like cells may be a mechanism for meningioma-induced hyperostosis, and that TRAF7 missense mutations may be gain-of-function drivers of meningioma cell transdifferentiation. Importantly, these data were derived from a single tumor, and efforts are underway to generalize our findings across hyperostotic meningiomas. Understanding mechanisms driving meningioma-induced hyperostosis may lead to new medical therapies for patients, or reveal novel pathways of bone formation.

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Artikel online veröffentlicht:
05. Februar 2024