Abstract Mesenchymal cells of the tumor-associated stroma are critical determinants of carcinoma cell behavior. We focus here on interactions of carcinoma cells with mesenchymal stem cells (MSC), which are recruited to the tumor stroma and, once present, are able to influence the phenotype of the carcinoma cells. We find that carcinoma cell–derived interleukin-1 (IL-1) induces prostaglandin E2 (PGE2) secretion by MSCs. The resulting PGE2 operates in an autocrine manner, cooperating with ongoing paracrine IL-1 signaling, to induce expression of a group of cytokines by the MSCs. The PGE2 and cytokines then proceed to act in a paracrine fashion on the carcinoma cells to induce activation of β-catenin signaling and formation of cancer stem cells. These observations indicate that MSCs and derived cell types create a cancer stem cell niche to enable tumor progression via release of PGE2 and cytokines. Significance: Although PGE2 has been implicated time and again in fostering tumorigenesis, its effects on carcinoma cells that contribute specifically to tumor formation are poorly understood. Here we show that tumor cells are able to elicit a strong induction of the COX-2/microsomal prostaglandin-E synthase-1 (mPGES-1)/PGE2 axis in MSCs recruited to the tumor-associated stroma by releasing IL-1, which in turn elicits a mesenchymal/stem cell–like phenotype in the carcinoma cells. Cancer Discov; 2(9); 840–55. ©2012 AACR. Read the Commentary on this article by Räsänen and Herlyn, p. 775. This article is highlighted in the In This Issue feature, p. 753.

Cancer-Stimulated Mesenchymal Stem Cells Create a Carcinoma Stem Cell Niche via Prostaglandin E2 Signaling