Methionine Restriction Exerts Anti-Tumor Immunity via Joint Intervention of T-Bet Palmitoylation in Gastric Cancer

Abstract

Background

Methionine restriction (MR) exerts an anti-tumor immunomodulatory role. Th1 cells facilitate CD8⁺ cytotoxic T cell activation and targeted tumor cell killing. Our previous work shows that MR enhances the immunotherapy effect of PD-L1/PD-1 blockade on gastric cancer, MR can simultaneously inhibit Th1 cell differentiation, which may affect their synergistic therapeutic outcome. We aim to elucidate the molecular mechanism of MR regulating Th1 cell activation in gastric cancer.

Methods

Murine Foregastric Carcinoma (MFC) cells were injected into 615 mice to establish transplanted tumor models, which were then treated with an MR diet or combined with 2-bromopalmitate (2-BP). CD4⁺T cells were cultured with deficient methionine. The acyl-biotinyl exchange (ABE) method was to detect T-bet palmitoylation and cycloheximide experiments to detect protein stability. GPS-Palm tool was employed to screen palmitoyltransferases. The impact of T-bet palmitoylation on the pro-tumor-killing effect of Th1 cells was examined.

Results

MR enhanced anti-PD-1's inhibition of tumor growth, while concurrently suppressing the increased Th1 cells. Combined with 2-BP further inhibited tumor and increased Th1 cells. Suppressing Th1 activity attenuated 2-BP's synergistic therapeutic effect and reduced CD8⁺ GZMB⁺ T cells. MR inhibited Th1 differentiation by reducing T-bet expression, 2-BP treatment restored, while T-bet interference reversed 2-BP's effect. MR increased palmitoylation and T-bet underwent palmitoylation modification. ZDHHC23 mediated T-bet palmitoylation and promoted T-bet degradation. MR promoted T-bet degradation, thereby decreasing T-bet content, inhibiting Th1 cell polarization and CD8⁺ T cell killing effect.

Conclusions

MR combined with T-bet palmitoylation intervention promotes Th1 polarization and CD8⁺ T cell toxicity, thereby enhancing anti-tumor immunity in gastric cancer.