High-fat diet plus HNF1A variant promotes polyps by activating β-catenin in early onset colorectal cancer.

The incidence of early onset colorectal cancer (EO-CRC) is rising and is poorly understood. Lifestyle factors and altered genetic background possibly contribute. Here we performed targeted exon sequencing of archived leukocyte DNA from 158 EO-CRC participants, which identified a missense mutation at p.A98V within the proximal DNA binding domain of Hepatic Nuclear Factor 1 alpha (HNF1AA98V, Rs1800574). The HNF1AA98V exhibited reduced DNA binding. To test function, the HNF1A variant was introduced into the mouse genome by CRISPR/Cas9 and the mice were placed on either a high fat (HFD) or high sugar diet (HSD). Only 1% of the HNF1A mutant mice developed polyps on normal chow; however,19% and 3% developed polyps on the HFD and HSD, respectively. RNA-Seq revealed an increase in metabolic, immune, lipid biogenesis genes and Wnt/β-catenin signaling components in the HNF1A mutant relative to the wildtype mice. Mouse polyps and colon cancers from subjects carrying the HNF1AA98V variant exhibited reduced CDX2 and elevated β-catenin proteins. We further demonstrated decreased occupancy of HNF1AA98V at the Cdx2 locus and reduced Cdx2 promoter activity compared to wildtype HNF1A. Collectively, our study shows that the HNF1AA98V variant plus HFD promotes the formation of colonic polyps by activating β-catenin via decreasing Cdx2 expression.