The role of miR-31 and its target gene SATB2 in cancer-associated fibroblasts

It is well established that there is a dynamic relationship between the expanding tumor and the host surrounding tissue. Cancer-associated fibroblasts (CAFs), the most common cellular population found in the tumor microenvironment, supporting tumor growth and dissemination. Here, we set out to determine the factors that may be involved in dramatic alteration of gene expression pattern in CAFs, focusing on microRNA and transcriptional regulators. We established matched pairs of human CAFs isolated from endometrial cancer and normal endometrial fibroblasts. MicroRNA and mRNA analyses identified differential expression of 11 microRNAs, with miR-31 being the most downregulated microRNA in CAFs (p=0.007). We examined several putative miR-31 target genes identified by microarray analysis and demonstrated that miR-31 directly targets the homeobox gene SATB2, which is responsible for chromatin remodeling and regulation of gene expression, and was significantly elevated in CAFs. The functional relevance of miR-31 and SATB2 were tested in in vitro models of endometrial cancer. Overexpression of miR-31 significantly impaired the ability of CAFs to stimulate tumor cell migration and invasion, without affecting tumor cell proliferation. Genetic manipulation of SATB2 levels in normal fibroblasts or CAFs showed that, reciprocally to miR-31, SATB2 increased tumor cell migration and invasion, while knock-down of endogenous SATB2 in CAFs reversed this phenotype. Introduction of SATB2 into normal fibroblasts stimulated expression of a number of genes involved in cell invasion, migration and scattering. These findings provide new insights into tumor-stroma interaction and document that miR