Histone serotonylation regulates ependymoma tumorigenesis.

Bidirectional communication between tumours and neurons has emerged as a key facet of the tumour microenvironment that drives malignancy. Another hallmark feature of cancer is epigenomic dysregulation, in which alterations in gene expression influence cell states and interactions with the tumour microenvironment. Ependymoma (EPN) is a paediatric brain tumour that relies on epigenomic remodelling to engender malignancy; however, how these epigenetic mechanisms intersect with extrinsic neuronal signalling during EPN tumour progression is unknown. Here we show that the activity of serotonergic neurons regulates EPN tumorigenesis, and that serotonin itself also serves as an activating modification on histones. We found that inhibiting histone serotonylation blocks EPN tumorigenesis and regulates the expression of a core set of developmental transcription factors. High-throughput, in vivo screening of these transcription factors revealed that ETV5 promotes EPN tumorigenesis and functions by enhancing repressive chromatin states. Neuropeptide Y (NPY) is one of the genes repressed by ETV5, and its overexpression suppresses EPN tumour progression and tumour-associated network hyperactivity through synaptic remodelling. Collectively, this study identifies histone serotonylation as a key driver of EPN tumorigenesis, and also reveals how neuronal signalling, neuro-epigenomics and developmental programs are intertwined to drive malignancy in brain cancer.