Abstract 64: Regulation and functional role of the cell-cell junction-associated RNAi machinery in colon cancer

Abstract

Abstract Colon cancer is the third most common and the second deadliest type of cancer in the United States. A typical characteristic of colon tumors is the compromised integrity of the colonic epithelial monolayer. The Adherens Junction (AJ) is a cell-cell adhesion complex essential for the maintenance of the epithelial integrity, composed of E-cadherin and the catenin family of proteins. We have recently shown that the E-cadherin-p120 catenin partner PLEKHA7 is critical for epithelial monolayer integrity. We have also revealed that PLEKHA7 recruits the core components of the RNA interference (RNAi) machinery, such as Ago2, DROSHA and DGCR8, as well as miRNAs at the mature apical adherens junctions, to suppress expression of pro-tumorigenic markers, through miRNA-mediated silencing. However, we still haven’t examined the extend of the contribution of this mechanism to colon tumorigenesis and its modes of regulation. We hypothesize that the adherens junction-RNAi mechanism acts as an epithelial sensor that tethers monolayer integrity to cell behavior. To examine this, we generated 3D cultures of well-differentiated Caco2 colon epithelial cells on Matrigel to examine the distribution of RNAi proteins. Indeed, co-localization of PLEKHA7 with RNAi proteins occurs specifically at the apical surface of these spheroids, whereas PLEKHA7 depletion results in loss of junctional localization of RNAi proteins and in enlarged, multilayered structures. Corroborating these results, PLEKHA7 and RNAi components co-localize specifically at the apical surface of normal colon crypts, whereas extensive disruption or loss of this co-localization was observed in colon tumor patient samples. Fibrosis and extensive deposition of extracellular matrix (ECM) due to chronic inflammation is a precursor to colon cancer. ECM can affect adherens junctions integrity, through integrin-Src signaling. Indeed, we have found that Src activity disrupts localization of PLEKHA7 and RNAi proteins to the junctions. To investigate the potential role of ECM in the regulation of the junctional RNAi mechanism, we are now examining Caco2 cells grown on different ECM substrates, as well as under different conditions of mechanical strain, since fibrosis poses mechanical stress on cells. In summary, our data point towards a novel putative tumor suppressor mechanism, of which we are investigating its modes of regulation and its involvement in colon tumorigenesis. Citation Format: Amanda C. Daulagala, Catherine Bridges, Lauren Rutledge, Joyce Nair-Menon, Micheal Yost, Antonis Kourtidis. Regulation and functional role of the cell-cell junction-associated RNAi machinery in colon cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 64.