Abstract
Carcinoma-associated fibroblasts (CAFs) are now widely appreciated for their contributions to tumor progression. However, the ability of CAFs to regulate anoikis, detachment-induced cell death, has yet to be investigated. Here, a new role for CAFs in blocking anoikis in multiple cell lines, facilitating luminal filling in three-dimensional cell culture, and promoting anchorage-independent growth is defined. In addition, a novel mechanism underlying anoikis inhibition is discovered. Importantly, it was demonstrated that CAFs secrete elevated quantities of insulin-like growth factor-binding proteins (IGFBPs) that are both necessary for CAF-mediated anoikis inhibition and sufficient to block anoikis in the absence of CAFs. Furthermore, these data reveal a unique antiapoptotic mechanism for IGFBPs: the stabilization of the antiapoptotic protein Mcl-1. In aggregate, these data delineate a novel role for CAFs in promoting cell survival during detachment and unveil an additional mechanism by which the tumor microenvironment contributes to cancer progression. These results also identify IGFBPs as potential targets for the development of novel chemotherapeutics designed to eliminate detached cancer cells. Implications: The ability of CAF-secreted IGFBPs to block anoikis in breast cancer represents a novel target for the development of therapeutics aimed at specifically eliminating extracellular matrix-detached breast cancer cells.