A GAPDH serotonylation system couples CD8+ T-cell glycolytic metabolism to antitumor immunity
The neuroimmune signaling axis involving serotonin (5-hydroxytryptamine, 5-HT) has been well acknowledged. Apart from the canonical 5-HT-receptor signaling transduction pattern, 5-HT-involved post-translational serotonylation has recently been noted. However, whether and how serotonylation affects immune cell function remains poorly understood. Using copper click chemistry and an unbiased proteomic approach, glyceraldehyde-3-phosphate dehydrogenase (GAPDH) was identified as the substrate for serotonylation in activated CD8+ T cells. Tissue transglutaminase 2 (TGM2) catalyzed the serotonylation reaction of GAPDH by covalently incorporating intracellular 5-HT into GAPDH Gln262 (Q262ser), resulting in enhanced cytoplasmic translocation and glycolytic activity. Glycolytic metabolism induced by GAPDH serotonylation supports the expression of the cytokine interferon γ (IFN-γ) and contributes to the antitumor ability of CD8+ T cells. Activated CD8+ T cells accumulate intracellular 5-HT for serotonylation through both cell-autonomous synthesis by tryptophan hydroxylase 1 (TPH1) and uptake from the extracellular compartment via serotonin transporter (SERT). Genetic ablation of TPH1 or SERT inhibits proliferation and IFN-γ production in CD8+ T cells, which subsequently impairs their antitumor immune activity. Monoamine oxidase A (MAOA) degrades intracellular 5-HT and acts as an intrinsic negative regulator of CD8+ T cells. Adoptive transfer of 5-HT-producing TPH1-overexpressing chimeric antigen receptor T (CAR-T) cells induced a robust antitumor response in mice. These findings reveal a GAPDH serotonylation system that promotes glycolytic metabolism and antitumor immune activity of CD8+ T cells.