P18.07.A Hippo signaling pathway is strongly involved in meningioma tumorigenesis

Abstract

Abstract Background Recurrent and aggressive meningiomas remain an unmet medical need in neuro-oncology. In mammals, Hippo signaling pathway is responsible for the growth of organs by regulating cell proliferation and apoptosis. The tumor suppressor NF2 protein belongs to the core of the Hippo pathway and a defect of its gene is present in 50% of meningiomas. Absence of NF2 keeps Hippo pathway inactive allowing the translocation of YAP/TAZ to the nucleus and the formation of a complex with TEADs. This complex then promotes the transcription of anti-apoptotic and proliferative genes such as CTGF, CYR61 and AXL. Here we present experimental results on human meningioma fragments and primary cell cultures supporting that Hippo pathway plays a critical role in meningioma tumorigenesis. Material and Methods The role of the Hippo pathway was studied on 57 meningiomas, well characterized at clinical, histological and molecular level. The genomic profile, target transcripts of the complex YAP/TAZ-TEADs, cell viability, and cell proliferation were analyzed after siRNA transfection targeting YAP, TAZ, YAP+TAZ and TEADs. Results Fifty-seven meningiomas were randomly selected including 27 WHO grade II and III tumors. Thirty (53%) presented a defect on the NF2 gene (NF2def) including 19(65%) grade II/III. NF2def meningiomas presented a significant increase of expression levels of Hippo pathway target transcripts CTGF, CYR61 and AXL in comparison with NF2 wild-type tumors (p<0.0001, p=0.0072 and p=0.0191, respectively). This increase was not correlated with the grade, the sex or with the cerebral localization of the meningiomas. On the other side, IHC analysis suggested this increase was correlated with the nuclear localization of YAP. Disturbing the YAP/TAZ-TEADs complex using siRNA on 10 meningiomas (5 NF2 wild-type and 5 NF2 def) induced a significant decrease on cell proliferation but not on cell viability. This decrease was more important when TAZ was turned off in comparison to turning off of YAP. Conclusion Our experimental results strongly support the importance of the Hippo pathway in meningioma tumorigenesis, supporting its relevance as a new target in meningioma therapy. A.Barlier reports receiving research grants from Inventiva Pharma. No potential conflicts of interest were disclosed by the other authors.