5-HT orchestrates serotonylation and lactylation to promote bladder cancer progression in a KIF20A-dependent pathway

5-HT is one neurotransmitter that also contributes to tumorigenesis. However, how 5-HT reshapes the tumor microenvironment remains unclear. Herein, we proposed that 5-HT reuptake inhibitor Fluoxetine inhibited bladder cancer progression through downregulating pan-lactylation level within cancer cells. Mechanically, on one hand, 5-HT serotonylated KIF20A at Q565 site within its nuclear-export signal via TGM2. Q565ser KIF20A was restricted into nucleus and this shielded KIF20A from experiencing ubiquitin-dependent degradation in cytoplasm. On the other hand, lactate mediated lactylation of Q565ser KIF20A at K242 site via AARS1. K242lac KIF20A underwent liquid-liquid phase separation to recruit P300 and elevated histone H3K18la modification level across target loci. Consequently, transcription of glut1 and hmgb1 were enhanced, fueling lactate accumulation and neutrophil extracellular traps formation. Neutrophil extracellular traps in turn secreted lactate and isolated cancer cells from CD8+ T cells. To sum up, 5-HT orchestrated a crosstalk between serotonylation and lactylation in bladder cancer. Targeting 5-HT pharmacologically exaggerated anti-tumor effects of immunotherapy in treating bladder cancer.