CXCL10 conditions alveolar macrophages within the premetastatic niche to promote metastasis

Formation of the premetastatic niche is triggered by primary tumors and contributes to cancer metastasis. Evidence indicating the roles of macrophages in metastatic niche formation and organ-specific metastatic tropism has been steadily accumulating. However, the role of tissue-resident macrophages in the establishment of the premetastatic niche is not clearly defined. Here, we report that alveolar macrophages (AMs), which are lung tissue-resident macrophages, play a critical role in initiating the recruitment of monocytic myeloid-derived suppressor cells (mo-MDSCs) and the subsequent premetastatic niche formation by increasing CCL12 expression. We found that CXCL10 can induce CCL12 expression by activating CXCR3 and TLR4 in AMs. CXCR3/TLR4 deficiency or inhibition of its activity reduces CCL12 expression in AMs and subsequent mo-MDSC recruitment to the premetastatic niche, thereby attenuating lung metastasis. In addition, Ube2o is a negative modulator of CXCL10-induced CCL12 expression. Downregulation of Ube2o in AMs under tumor conditions enhances TAK1-NF-κB/ERK/JNK signaling and CXCL10-induced CCL12 expression by promoting TRAF6 polyubiquitination and inhibiting DDX3X degradation. Targeting mo-MDSC recruitment via the CXCL10-CXCR3/TLR4-CCL12 axis in AMs may have therapeutic potential for suppressing lung metastasis.