Abstract
APC mutation activation of Wnt/β-catenin drives initiation of colorectal carcinogenesis (CRC). Additional factors potentiate β-catenin activation to promote CRC. Western diets are enriched in linoleic acid (LA); LA-enriched diets promote chemically induced CRC in rodents. 15-Lipoxygenase-1 (15-LOX-1), the main LA-metabolizing enzyme, is transcriptionally silenced during CRC. Whether LA and 15-LOX-1 affect Wnt/β-catenin signaling is unclear. We report that high dietary LA promotes CRC in mice treated with azoxymethane or with an intestinally targeted Apc mutation (ApcΔ580) by upregulating Wnt receptor LRP5 protein expression and β-catenin activation. 15-LOX-1 transgenic expression in mouse intestinal epithelial cells suppresses LRP5 protein expression, β-catenin activation, and CRC. 15-LOX-1 peroxidation of LA in phosphatidylinositol-3-phosphates (PI3P_LA) leads to PI3P_13-HODE formation, which decreases PI3P binding to SNX17 and LRP5 and inhibits LRP5 recycling from endosomes to the plasma membrane, thereby increasing LRP5 lysosomal degradation. This regulatory mechanism of LRP5/Wnt/β-catenin signaling could be therapeutically targeted to suppress CRC.