The NF-κB/AKT-dependent Induction of Wnt Signaling in Colon Cancer Cells by Macrophages and IL-1β

Abstract

Progression of colon cancer from microadenoma to macroscopic tumors is coupled to augmentation of canonical Wnt signaling. We recently reported that tumor associated macrophages, through interleukin 1β (IL-1β) dependent phosphorylation of GSK3β, promote Wnt signaling in colon cancer cells, demonstrating that proinflammatory cytokines can enhance TCF4/β-catenin transcriptional activity in tumor cells. Here we investigated the pathway whereby IL-1β inactivates GSK3β and promotes Wnt signaling in colon cancer cells. We showed that normal human monocytes, THP1 macrophages and IL-1 failed to induce Wnt signaling in tumor cells expressing dominant negative IκB (dnIκB), demonstrating that macrophages and IL-1 activate Wnt signaling in a NF-κB-dependent manner. NF-κB activity was required for macrophages and IL-1 to activate PDK1 and AKT in tumor cells and thereby inhibit GSK3β activity. Consistently, dominant negative AKT (dnAKT), or pharmacological inhibition of AKT in tumor cells, prevented macrophage/IL-1 mediated phosphorylation of GSK3β, activation of Wnt signaling, and induction of c-jun and c-myc, confirming that macrophages and IL-1 promote Wnt signaling in an AKT dependent manner. Finally, we showed IL-1 and macrophages failed to promote growth of colon cancer cells with impaired NF-κB or AKT signaling, confirming the requirement for NF-κB and AKT activation for the protumorigenic activity of tumor associated macrophages. Thus, we showed that IL-1 and tumor associated macrophages activate NF-κB-dependent PDK1/AKT signaling in tumor cells, and thereby inactivate GSK3β, enhance Wnt signaling and promote growth of colon cancer cells, establishing a novel molecular link between inflammation and tumor growth.