Abstract 419: PKD1 regulates susceptibility to ulcerative colitis and colorectal cancer
Authors: Nikonova Anna S. , Kiseleva Anna A. , Deneka Alexander , Tricarico Rossella , Grivennikov Sergei , Golemis Erica 
Published: September 2020

Abstract
Compromised barrier function of colon epithelial tissue is associated with inflammatory bowel diseases (IBDs), and increases the risk of colorectal cancer (CRC) through a process of tumor-elicited inflammation (TEI). Apical tight junction (TJ) proteins, including ZO-1, occludin and specific claudins, are critical in the maintenance of epithelial barrier function and control of paracellular permeability. Changes in TJ composition in the kidney are strongly linked to the etiology of autosomal dominant polycystic kidney disease (ADPKD), with ADPKD-inducing mutations in PKD1 causing non-leaky barriers that can withstand high hydrostatic pressure within renal cysts a hallmark of this common (~1 in 600) inherited disease. Intriguingly, a large population study suggested decreased incidence of CRC in ADPKD patients, while other studies implicated PKD1 in control of epithelial-mesenchymal transition (EMT) and invasion. Based on these data, we hypothesized that loss of PKD1 might hinder susceptibility to ulcerative colitis and CRC, based on reorganization of TJs and limitation of TEI in the colon.
We directly assessed PKD1 control of epithelial barrier function using conditional Pkd1fl/fl mice in which tamoxifen induces Cre-lox dependent targeted inactivation of Pkd1 gene in the colon. We compared 10-12 week old wt or induced Pkd1fl/fl mice treated for 5 days with 2.5% DSS in drinking water to induce colitis, to a non-DSS control group. For wt mice, DSS increased orally gavaged FITC-dextran in the serum versus vehicle-treated mice, and histopathological assessment indicated significant damage to colon. In contrast, DSS did not increase FITC-dextran in the serum of Pkd1−/- mice, and less DSS-induced tissue damage was observed, suggesting reinforced colon barrier function. Further, based on immunofluorescence (IF) analysis of tissue sections, the claudins CLDN4 and CLDN7, associated with barrier impermeability, were strongly elevated in the colonic epithelium of Pkd1fl/fl versus wt mice, with consistently greater localization to cell junctions in Pkd1fl/fl versus wt mice.
Using a Cdx2-ERT2/Cre model for tamoxifen-induced loss of Apc and/or Pkd1 in the colon, we compared tumorigenesis in the Apcfl/fl, Apcfl/fl Pkd1fl/fl, and Apcfl/flPkd1fl/+ genotypes. There was a highly significant increase in the number and size of Apcfl/fl-induced tumors based on retention of Pkd1. Loss of Pkd1 substantially increased CLDN4 in normal and tumor tissue, and decreased TNFα expression in tumors, suggesting reduced inflammation. Analysis in organoids recapitulated observed effects of Pkd1, indicating cell-autonomous effect. Epistasis experiments suggest activation of the tumor suppressor CFTR as a mechanism by which loss of PKD1 limits EMT and tumor growth; we found chemical activators of CFTR selectively limited the growth of PKD1-positive organoids. Better understanding of the role of PKD1 and its effectors may suggest therapeutic strategies, and inform genetic counseling, for IBD and CRC.
Citation Format: Anna S. Nikonova, Anna A. Kiseleva, Alexander Deneka, Rossella Tricarico, Sergei Grivennikov, Erica Golemis. PKD1 regulates susceptibility to ulcerative colitis and colorectal cancer [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 419.