Enrichment of AU-rich Element Containing mRNAs during Intestinal Cell Epithelial-mesenchymal Transition: Roles, Mechanisms, and Significance

Abstract

Colon cancer progression is frequently characterized by activating mutations in Ras and emergence of the tumor promoting effects of TGF-beta signaling. Ras-inducible rat intestinal epithelial cells (RIE:iRas) undergo a well described epithelial to mesenchymal transition (EMT), acquiring an invasive phenotype in response to H-RasV12 expression and TGF-beta treatment, modeling tumor progression. The gene expression profile accompanying Ras and TGF-beta-induced EMT in RIE:iRas cells was characterized by microarray analysis. Ras and TGF-beta cooperatively regulate 329 transcripts during EMT, many of which are of known importance in tumor progression. In particular, several EGF family receptors and ligands, which are shown here to be necessary for TGF-beta-induced EMT in both RIE:iRas and LIM1863 human colorectal cancer cells, were shown to be synergistically regulated by these combined treatments. In addition, enrichment of a class of mRNAs containing 3’ AU-rich element (ARE) motifs known to regulate mRNA stability were synergistically regulated by Ras and TGF-beta. Among these, vascular endothelial growth factor (VEGF), a key regulator of tumor angiogenesis, was synergistically regulated in both RIE:iRas cells as well as in an independent cell culture model (YAMC) and was further shown to be regulated by a post-transcriptional mechanism. Expression profiling of human colorectal cancers (CRC) further revealed that many of the ARE-containing genes were differentially expressed in stage 4 human colon adenocarcinomas compared to adenomas. Furthermore, genes differentially expressed in CRC are also significantly enriched with ARE-containing transcripts. These studies demonstrate that oncogenic Ras and TGF-beta globally regulate genes containing AREs in association with EMT by a post-transcriptional mechanism with potential clinical significance.