PLA2G16-Mediated Tetracosatetraenoic Acid Rewires Fatty Acid Oxidation to Impair CD8+ T Cell Immune Function in Promoting Breast Cancer Lung Metastasis.

Tumor-related metabolites in the tumor microenvironment may induce immune dysfunction, leading to malignant progression and metastasis of tumors. Here, it is demonstrated that tumoral PLA2G16, a phospholipase catalyzes phospholipids to generate free fatty acid (FFA) or lysophosphatidic acid (LPA), is an important contributor to triple-negative breast cancer (TNBC) lung metastasis in an immune-dependent pattern by improving tetracosatetraenoic acid (C24:4 (n-6)) accumulation in the early metastatic niche of lung and impairing immune function of pulmonary CD8+ T cells. C24:4 (n-6) induces nuclear import of PPARα in pneumal CD8+ T cells, which regulates the transcription of Cpt1a, Dgat1, Cd36, and Fabp1, leading to the activation of fatty acid oxidation (FAO). The robust FAO results in suppression of CD8+ T cells. Genetically depleting PPARα in mice, pharmacologically inhibiting C24:4 (n-6)-induced PPARα in the nucleus or directly suppressing PPARα activity effectively attenuates PLA2G16-C24:4 (n-6) axis-based immune dysfunction of CD8+ T cells and their according anti-tumor activities. These results imply that PLA2G16-mediated C24:4 (n-6) accumulation in the lung acts as a metabolic disorder to CD8+ T cell antitumor activity and highlights a critical role of PLA2G16 in promoting TNBC lung metastasis. Targeting PLA2G16 and combination with anti-PD-1-based immunotherapy may be an effective strategy for clinical tumor immunotherapy.