1810P Tumor metabolite lactate promotes tumorigenesis through modulating Moesin lactylation and TGF-b signaling of regulatory T cells

Tregs, which are characterized by Foxp3, play a vital role in maintaining immune homeostasis. Previous studies had revealed the critical role of Tregs in sustaining tumor microenvironment and accelarating tumorigenesis and recurrence through suppressing T cells activation and immune surveillance. Several studies had shown that lactate is a critical metabolite in cancer and relates to the tumor prognosis, metastases and overall survival of patients. To analyze the impacts and the mechanism of lactate on Tregs. Lactate was added to the culture system during mice-Treg induction, and the function of Tregs was evaluated through flow cytometry test. IL-1 and IL-6 was also added to test the stability of Tregs under inflammatory enviorment. The level of protein lactylation of Tregs was determined by pan anti-lactyllysine antibody, possible lactylation sites related to Tregs was selected and confirmed by using antagonist. CO-IP was used to analyze the underline mechanism. In vitro experiment showed that the Foxp3 expression, stability and function were improved with lactate induction. Lactate degradation by lactate dehydrogenase inhibitor resulted in the reduction of Tregs and decreasion of tumor growth in mice. Mechanism study showed that lactate modulated lactylation of Tregs. We filtrated four potential protein lactylation sites related to Tregs and generated the antibody for each sites. Antagonist of Moesin Lys72 lactylation suppressed the effect of lactate on Tregs. Structure, Co-IP and TGF-b downstream signal examination discovered that lactylation of Moesin improved the interaction between Moesin and TGF-b R and improved smad signal, by using anti-Moesin Lys72 lactylation antibody, the improve of Treg in vitro and aggressived Tumor growth are both abolished. Finally, we evaluated the combination of anti-lactate treatment with PD-1 therapy, which showed that the combination reduced the tumor genesis by reducing Tregs comparing with PD-1 alone. Finally, we identify lactate as an essential small molecule in reinforcing Tregs in the tumor microenvironment through Moesin lactylation, thus moesin or lactate serves as an potential anti-cancer immunotherapeutic target.