FOXP3 Transcriptionally Activates Fatty Acid Scavenger Receptor CD36 in Tumour-Induced Treg Cells

Abstract

The host immune system is adapted in a variety of ways by tumour microenvironment and growing tumour interacts to promote immune escape. One of these adaptations is manipulating the metabolic processes of cells in the tumour microenvironment. The growing tumour aggressively utilise glucose, its primary energy source available in tumour site, and produce lactate by Warburg effect. In such a hostile environment, tumour-infiltrating immune cells are unable to survive metabolically. Tumour-infiltrating CD4⁺ Treg cells, on the other hand, adapted to an alternative energy-generating system, switching from the highly-competitive glucose to the fatty-acid metabolic pathway, by down-regulating glucose-metabolising genes and up-regulating fatty-acid metabolising genes. Tregs with high-levels of the fatty acid scavenger receptor CD36, a key component of the fatty-acid metabolic pathway, aided this metabolic shift. Treg cell formation was hampered when the fatty-acid metabolic pathway was disrupted, showing that it is necessary for Treg cell development. FOXP3, the Treg lineage-specific transcription factor, regulates fatty-acid metabolism by inducing CD36 transcription. A high-fat diet enhanced Treg development while suppressing anti-tumour immunity, whereas a low-fat diet suppressed Treg development. The altered metabolism of tumour-infiltrating Treg cells enables their rapid generation and survival in the hostile tumour microenvironment, aiding cancer progression. Fascinatingly, mice fed with a low-fat diet showed a positive prognosis with chemotherapy than mice fed with a high-fat diet. Thus, a maximum efficacy of chemotherapy might be achieved by altering diet composition during chemotherapy, providing a promising indication for future cancer treatment.

Keywords: CD36; Treg; cancer; metabolism; tumour microenvironment.