Interleukin-32θ inhibits tumor-promoting effects of macrophage-secreted CCL18 in breast cancer

BackgroundTumor-associated macrophages can promote breast cancer metastasis by secreting cytokines and growth factors. Interleukin (IL)-32, a newly identified IL-32 isoform, was previously shown to down-regulate various proinflammatory factors of macrophages. Here, we report the presence of IL-32 in breast cancer tissues and evaluate its effects on macrophage-regulated breast cancer metastasis.MethodsRT-qPCR was used to analyze the mRNA expression of IL-32, Chemokine (C-C motif) ligand 18 (CCL18) in breast cancer tissues. In vitro cell-based experiments using IL-32-expressing MDA-MB-231 cells were conducted to examine the effects of IL-32 on metastasis and its molecular signaling. In vivo xenograft, immunohistochemistry, and optical imaging models were generated to support in vitro and clinical findings.ResultsThe clinical data displayed opposite expression patterns of CCL18 and IL-32 mRNA in macrophage-infiltrated breast tumor tissues compared with those in the other tissues tested. In MDA-MB-231 cells, IL-32 overexpression attenuated migration, invasion, tumor-promoting factors, and increased epithelial markers levels upon treatment with conditioned media from THP-1-derived macrophages. Additionally, IL-32 expression in a xenograft model led to a remarkable decrease in tumor size and macrophage-stimulated tumor promotion. This inhibition was mediated through a direct interaction with protein kinase C- (PKC), subsequently eliminating the downstream factors STAT3 and NF-B. Blocking CCL18 during co-culture of macrophages and breast cancer cells reduced the levels of breast cancer progression-related factors and PKC downstream signaling suggesting CCL18 as the main macrophage-secreted factors triggering the signaling pathway inhibited by IL-32.ConclusionsOur findings demonstrate a novel role of IL-32 as an intracellular modulator to suppress macrophage-promoted breast cancer progression by targeting CCL18-dependent signaling.