Pleiotropic effects of PPARD accelerate colorectal tumorigenesis, progression, and invasion

APC mutations activate aberrant β-catenin signaling to drive initiation of colorectal cancer (CRC), however, CRC progression requires additional molecular mechanisms. PPAR-delta (PPARD), a downstream target of β-catenin, is upregulated in CRC. However, promotion of intestinal tumorigenesis following deletion of PPARD in Apcmin mice has raised questions about the effects of PPARD on aberrant β-catenin activation and CRC. In this study, we used mouse models of PPARD overexpression or deletion combined with APC mutation (ApcΔ580) in intestinal epithelial cells (IEC) to elucidate the contributions of PPARD in CRC. Overexpression or deletion of PPARD in IEC augmented or suppressed β-catenin activation via up- or downregulation of BMP7/TAK1 signaling and strongly promoted or suppressed CRC, respectively. Depletion of PPARD in human CRC organoid cells inhibited BMP7/β-catenin signaling and suppressed organoid self-renewal. Treatment with PPARD agonist GW501516 enhanced CRC tumorigenesis in ApcΔ580 mice, whereas treatment with PPARD antagonist GSK3787 suppressed tumorigenesis. PPARD expression was significantly higher in human CRC invasive fronts versus their paired tumor centers and adenomas. Reverse-phase protein microarray and validation studies identified PPARD-mediated upregulation of other pro-invasive pathways: connexin 43, PDGFRβ, AKT1, EIF4G1, and CDK1. Our data demonstrate that PPARD strongly potentiates multiple tumorigenic pathways to promote CRC progression and invasiveness.

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