Compromised epithelial integrity is a hallmark of gastrointestinal diseases, such as inflammatory bowel disease and colon cancer, which is the third most prevalent and lethal form of cancer. The high incidence rates of these diseases suggest that we still do not fully understand the underlying mechanisms connecting epithelial architecture and cell behavior. Recently, we discovered a mechanism that links epithelial tissue integrity with the RNA interference (RNAi) machinery and with miRNA regulation. In particular, we have shown that the adherens junctions, which is an essential architectural component of the cell, recruit the microprocessor and the RNAi- induced silencing complex (RISC), the core components of the RNAi machinery, as well as a specific set of miRNAs, in colon epithelial cells. This interaction occurs through PLEKHA7, a novel partner of the E-cadherin cell-cell adhesion complex. PLEKHA7 loss results in compromised epithelial integrity, decreased levels and activity of a set of miRNAs and in increased anchorage-independent growth, an indicator of epithelial transformation. Importantly, our preliminary data show extensive mis-localization or loss of PLEKHA7 in colon cancer cell lines and tumor patient samples. Interestingly, an RNA-CLIP experiment followed by RNA sequencing revealed association of PLEKHA7 with a large set of long non-coding RNAs (lncRNAs). LncRNAs can interact with miRNAs and the RNAi machinery in multiple ways and a number of them has been implicated in intestinal diseases. However, our knowledge on lncRNA regulation and function is still limited. Our preliminary data show that PLEKHA7 loss results in dysregulation of a number of these lncRNAs, including upregulation of MIR17HG, which is a known oncogenic lncRNA and a strong promoter of cellular transformation. We hypothesize that the adherens junctions recruit and regulate the RNAi machinery and lncRNAs to maintain colon epithelial homeostasis. We will examine our hypothesis under the following Specific Aims: 1) PLEKHA7 suppresses MIR17HG by recruiting RISC and miRNAs at the adherens junctions; 2) PLEKHA7 maintains the normal colon epithelial phenotype by suppressing MIR17HG. This study is significant, since it provides a missing mechanistic link between epithelial architecture and cell behavior, as well as a new unexpected localized regulation of lncRNAs, which may be critical the maintenance of the normal colonic phenotype. The proposed work is innovative, because it tethers two previously unrelated fields, cell-cell adhesion and lncRNA biology. The impact of the study is that it will advance our understanding of the underlying mechanistic causes of intestinal diseases and will lay the foundation for the systematic interrogation of the newly discovered connection between the adherens junctions, the RNAi machinery and lncRNAs.
