TH2 cytokines promote tumor progression via regulating cathepsin secretion in tumor-associated macrophages

Tumor-associated macrophages (TAMs) have emerged as prominent cells within the tumor microenvironment playing critical roles in extracellular matrix remodeling, tumor cell proliferation and invasion, angiogenesis, and metastasis. Cathepsin proteases, produced by tumor cells and TAMs, have been demonstrated to mediate these processes, but it still remains unclear how these typically lysosomal enzymes are capable of executing their functions in the extracellular space. Here we identify a novel interaction between STAT6 and STAT3 that potently upregulates cathepsin secretion in macrophages in response to TH2 cytokine stimulation. Systematic gene expression analyses reveal that the TH2 cytokine IL-4 synergizes with IL-6 or IL-10 to activate the IRE1/ XBP1 axis of the unfolded protein response. Pharmacological inhibition of the IRE1 axis blunts cathepsin secretion in macrophages and blocks macrophage-mediated tumor cell invasion. Finally, we show that genetic ablation of either STAT6 or STAT3 signaling impairs tumor development and invasion. Thus, these findings demonstrate that TH2 cytokine-mediated STAT6 and STAT3 activation in macrophages promotes a professional secretory phenotype capable of enhancing tumor cell invasion in a cathepsin-dependent manner.

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