Proteome and secretome of human mammary normal fibroblasts and CAF

The secretome of cancer and stromal cells generates a microenvironment which contributes to tumour cell invasion and angiogenesis. Here, we compare the secretome of human mammary normal fibroblasts and cancer-associated fibroblasts (CAF). We discover that the chloride intracellular channel protein 3 (CLIC3) is an abundant component of the CAF secretome. Secreted CLIC3 promotes invasive behaviour of endothelial cells to drive angiogenesis and increases invasiveness of cancer cells both in vivo and in 3D cell culture models, and this requires active transglutaminse-2 (TGM2). CLIC3 acts as a glutathione-dependent oxidoreductase which reduces TGM2 and regulate TGM2 binding to its cofactors. Finally, CLIC3 is secreted also by cancer cells, is abundant in the stromal and tumour compartments of aggressive ovarian cancers, and its levels correlate with poor clinical outcome. This work reveals an unprecedented invasive mechanism whereby the secretion of a glutathione-dependent oxidoreductase drives angiogenesis and cancer progression by promoting TGM2-dependent invasion.