IL-33 activates tumor stroma to promote intestinal polyposis

Tumor epithelial cells develop within a microenvironment consisting of extracellular matrix, growth factors, and cytokines produced by non-epithelial stromal cells. In response to paracrine signals from tumor epithelia, stromal cells modify the microenvironment to promote tumor growth and metastasis. Here, we identify interleukin (IL)-33 as an epithelial cell-derived regulator of stromal cell activation and mediator of intestinal polyposis. IL-33 expression was elevated in the tumors and serum of colorectal cancer patients and induced in the adenomatous polyps of ApcMin/+ mutant mice. Genetic and antibody suppression of IL-33 signaling in ApcMin/+ mice inhibited proliferation, induced apoptosis, and suppressed angiogenesis in polyps, which reduced both tumor number and size. In ApcMin/+ polyps, IL-33 expression localized to tumor epithelial cells and expression of the IL-33 receptor, IL1RL1, associated with two stromal cell types, namely subepithelial myofibroblasts (SEMFs) and mast cells, whose activation was previously associated with polyposis. In vitro IL-33 stimulation of human SEMFs induced the expression of extracellular matrix components and growth factors associated with intestinal tumor progression. IL-33 deficiency reduced mast cell accumulation in ApcMin/+ polyps and expression of mast cell-derived proteases and cytokines known to promote polyposis. Together, our results suggest that IL-33 is a tumor epithelial cell-derived paracrine signal that promotes polyposis through the coordinated activation of stromal cells and the formation of a reactive stroma microenvironment. Overall design: Six T-75 flasks of CCD-18Co cells were grown to 80% confluency; three were treated with rhIL-33, three were given vehicle control; cells were trypsinized and split in two--half of each flask used for sequencing and half for qPCR validation post-sequencing