5-HT orchestrates Histone Serotonylation and Citrullination to Drive Neutrophil Extracellular Traps and Liver Metastasis.

Serotonin (5-HT) is a neurotransmitter that has been linked to tumorigenesis. Whether and how 5-HT modulates cells in the microenvironment to regulate tumor metastasis remains to be largely unknown. Here, we demonstrate that 5-HT is secreted by neuroendocrine prostate cancer (NEPC) cells to communicate with neutrophils and to induce neutrophil extracellular traps (NETs) in the liver, which in turn facilitates the recruitment of disseminated cancer cells and promotes liver metastasis. 5-HT induces histone serotonylation (H3Q5ser) and orchestrates histone citrullination (H3cit) in neutrophils to trigger chromatin decondensation and facilitate the formation of NETs. Interestingly, we uncover in this process a reciprocally reinforcing effect between H3Q5ser and H3cit and a crosstalk between the respective writers TGM2 and PAD4. Genetic ablation or pharmacological targeting of TGM2, or inhibiting 5-HT transporter (SERT) with the FDA-approved antidepressant drug fluoxetine reduces H3Q5ser and H3cit modifications, suppresses NETs formation, and effectively inhibits NEPC, small cell lung cancer, and thyroid medullary cancer liver metastasis. Collectively, the 5-HT-triggered NETs production highlights a new targetable neurotransmitter-immune axis in driving liver metastasis of neuroendocrine cancers.