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.
Keywords: AMs; CCL12; CXCL10; Premetastatic niche; mo-MDSCs.
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