Autocrine WNT2 signaling in fibroblasts promotes colorectal cancer progression.

The canonical WNT signaling pathway is crucial for intestinal stem cell renewal and aberrant WNT signaling is an early event in colorectal cancer (CRC) development. Here, we show for the first time that WNT2 is one of the most significantly induced genes in CRC stroma as compared to normal stroma. The impact of stromal WNT2 on carcinoma formation or progression was not addressed so far. Canonical WNT/ß-catenin signaling was assessed using a 7TGP-reporter construct. Furthermore, effects of WNT2 on fibroblast migration and invasion were determined using siRNA-mediated gene silencing. Tumor cell invasion was studied using organotypic raft cultures and in vivo significance was assessed via a xenograft mouse model. We identified cancer-associated fibroblasts (CAFs) as the main source of WNT2. CAF-derived WNT2 activated canonical signaling in adenomatous polyposis coli/ß-catenin wild-type colon cancer cells in a paracrine fashion, whereas no hyperactivation was detectable in cell lines harboring mutations in the adenomatous polyposis coli/ß-catenin pathway. Furthermore, WNT2 activated autocrine canonical WNT signaling in primary fibroblasts, which was associated with a pro-migratory and pro-invasive phenotype. We identified FZD8 as the putative WNT2 receptor in CAFs. Three-dimensional organotypic co-culture assays revealed that WNT2-mediated fibroblast motility and extracellular matrix remodeling enhanced cancer cell invasion of cell lines even harboring mutations in the adenomatous polyposis coli/ß-catenin pathway. Thus, suggesting a tumor-promoting influence on a broad range of CRC. In line, WNT2 also promotes tumor growth, invasion and metastasis in vivo. Moreover, high WNT2 expression is associated with poor prognosis in human CRC. The identification of the pro-malignant function of stromal derived WNT2 in CRC classifies WNT2 and its receptor as promising stromal targets to confine cancer progression in combination with conventional or targeted therapies.

IGFBP7, a novel tumor stroma marker, with growth-promoting effects in colon cancer through a paracrine tumor-stroma interaction.

The activated tumor stroma participates in many processes that control tumorigenesis, including tumor cell growth, invasion and metastasis. Cancer-associated fibroblasts (CAFs) represent the major cellular component of the stroma and are the main source for connective tissue components of the extracellular matrix and various classes of proteolytic enzymes. The signaling pathways involved in the interactions between tumor and stromal cells and the molecular characteristics that distinguish normal 'resting' fibroblasts from cancer-associated or '-activated' fibroblasts remain poorly defined. Recent studies emphasized the prognostic and therapeutic significance of CAF-related molecular signatures and a number of those genes have been shown to serve as putative therapeutic targets. We have used immuno-laser capture microdissection and whole-genome Affymetrix GeneChip analysis to obtain transcriptional signatures from the activated tumor stroma of colon carcinomas that were compared with normal resting colonic fibroblasts. Several members of the Wnt-signaling pathway and gene sets related to hypoxia, epithelial-to-mesenchymal transition (EMT) and transforming growth factor-ß (TGFß) pathway activation were induced in CAFs. The putative TGFß-target IGFBP7 was identified as a tumor stroma marker of epithelial cancers and as a tumor antigen in mesenchyme-derived sarcomas. We show here that in contrast to its tumor-suppressor function in epithelial cells, IGFPB7 can promote anchorage-independent growth in malignant mesenchymal cells and in epithelial cells with an EMT phenotype when IGFBP7 is expressed by the tumor cells themselves and can induce colony formation in colon cancer cells co-cultured with IGFBP7-expressing CAFs by a paracrine tumor-stroma interaction.