Inhibition of the cancer stem cell immune checkpoint SOAT1 suppresses regulatory T cell functions through a trans-cellular 20(S)-Hydroxycholesterol-GPR132 pathway in mice.

SOAT1 (sterol O-acyltransferase 1) serves as a cancer stem cell-specific immune checkpoint that facilitates trans-cellular signaling through the release of 20-Hydroxycholesterol (20-OHC) and subsequent activation of GPR132 on regulatory T cells (Tregs). This pathway plays a crucial role in modulating the tumor immune microenvironment and can significantly influence the balance between immune activation and suppression. In the context of cancer, SOAT1 is instrumental in regulating the cholesterol metabolism of cancer stem cells. When SOAT1 is inhibited, there is an increase in the secretion of 20-OHC by tumor cells. This oxysterol not only functions as a signaling molecule but also acts as a ligand that binds to GPR132, a G protein-coupled receptor primarily expressed on immune cells, including Tregs. This binding triggers a cascade of intracellular signaling pathways that ultimately enhances the immunosuppressive functions of Tregs. Mechanistically, the activation of GPR132 by 20-OHC leads to downstream signaling events that may involve pathways such as JAK-STAT and PKC signaling, promoting the development and survival of Tregs while enabling them to exert their immunosuppressive effects within the tumor microenvironment. This results in the downregulation of effector T cell activities and impairs the maturation and activation of dendritic cells (DCs), which are pivotal for effective anti-tumor immune responses. The presence of Tregs, particularly in elevated frequencies within tumors, can contribute to an immunosuppressive environment that protects cancer cells from immune-mediated destruction. Thus, the SOAT1-20OHC-GPR132 axis represents a critical mechanism through which cancer cells can evade immune surveillance. By controlling cholesterol metabolism through SOAT1, tumors can manipulate the availability of 20-OHC, amplifying the immunosuppressive capacity of Tregs and facilitating an environment conducive to tumor growth and progression. Targeting SOAT1 and the associated 20-OHC signaling pathway may offer a promising therapeutic strategy to neutralize Treg-mediated immunosuppression. Inhibiting SOAT1 not only disrupts the tumor's ability to produce 20-OHC but also potentially reprograms the immune landscape, promoting a more activated and effective anti-tumor immune response. Overall, SOAT1's dual role as a cancer stem cell-specific immune checkpoint and its involvement in the trans-cellular signaling of 20-OHC make it a valuable target for innovative cancer immunotherapies aimed at enhancing immune recognition and attack on cancer cells.