Background: Tumor-associated macrophages (TAMs) in the tumor microenvironment influence tumor initiation, invasion and metastasis. Several studies have shown that Wnt5a is mainly expressed in the tumor stroma, especially in TAMs. However, whether Wnt5a regulates the polarization and biological function of TAMs in colorectal cancer (CRC) is incompletely understood. Methods: Immunofluorescence staining was performed to detect CD68 and Wnt5a expression in colorectal tissues from patients (63 CRC specimens VS 20 normal tissues). RT-qPCR, flow cytometry, ELISA and inhibitors were carried out to explore the role of Wnt5a in the polarization of TAMs. Clone formation and transwell assays were performed to determine the effects of Wnt5a-treated macrophages on tumor proliferation, migration and invasion in vitro. Finally, a xenograft model was applied to confirm the effects of Wnt5a + TAMs on CRC tumorigenesis. Results: We found that high Wnt5a + CD68 + /CD68 + TAMs ratio was significantly associated with poor prognosis in CRC patients and Wnt5a + TAM was an M2-like TAM subtype. Subsequently, we found that Wnt5a induced macrophages to secrete IL-10, which then acted as an autocrine cytokine to induce M2 polarization of these macrophages. IL-10 neutralizing antibody completely reversed the pro-M2 effect of Wnt5a. Mechanistically, the CaKMII-ERK1/2-STAT3 pathway was required for Wnt5a-mediated IL-10 expression in macrophages. Furthermore, Wnt5a-induced M2 macrophages promoted CRC cells proliferation, migration and invasion; knockdown of Wnt5a in TAMs significantly impaired the pro-tumor functions of TAMs. Conclusions: Our data indicate that Wnt5a could induce M2 polarization of TAMs by regulating CaKMII-ERK1/2-STAT3 pathway-mediated IL-10 secretion, ultimately promoting tumor growth and metastasis of CRC.

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Background Metastasis is the main cause of death in colorectal cancer (CRC). Circulating tumour cells (CTCs) are regarded as the precursor cells of metastasis. The CTCs, which underwent epithelial‐mesenchymal transition (EMT), are associated with metastasis and responsible for poor prognosis. EMT cancer cells modulate endothelial permeability in the invasive front and facilitate cancer cell intravasation, resulting in CTCs‐mediated distant metastasis. Exosomes derived from cancer cells are key mediators of cancer‐host intercommunication. However, the mechanism by which EMT‐tumour cells‐derived exosomes modulate vascular permeability and promote CTCs generation has remained unclear. Methods Exosomes isolation and purification were conducted by ultra‐centrifugation. Exosomal miRNA was identified by sequencing followed by quantitative PCR. In vitro co‐culture assay experiments were conducted to evaluate the effect of exosomal miR‐27b‐3p on the permeability of blood vessel endothelium. Dual‐luciferase reporter assay, chromatin immunoprecipitation (ChIP) and RNA immunoprecipitation (RIP) were performed to investigate the underlying mechanism by which miR‐27b‐3p is packaged into exosomes. A mouse model was established to determine the role of exosomal miR‐27b‐3p in blood vessel permeability modulation in vivo. Results We found that EMT‐CRC cells attenuate the blood vessel barrier by transferring miR‐27b‐3p to human umbilical vein endothelial cells (HUVECs) in exosomes. Mechanically, miR‐27b‐3p atteuated the expression of vascular endothelial cadherin (VE‐Cad) and p120 at the post‐transcriptional level by binding to 3′‐untranslated region of VE‐Cad and p120 directly. The packaging of miR‐27b‐3p into exosomes was induced by heterogeneous nuclear ribonucleoprotein A1 (hnRNPA1), which activated by STAT3. Clinically, miR‐27b‐3p up‐regulated in CRC tissues. Plasma exosomal miR‐27b‐3p was positively correlated with malignant progression and CTC count in CRC patients. Our study reveals a novel mechanism by which EMT‐CRC cells promote metastasis, increasing blood vessel permeability and facilitating the generation of CTCs. Conclusion Exosomal miR‐27b‐3p secreted by EMT‐CRC cells increases blood vessel permeability and facilitates the generation of CTCs. Exosomal miR‐27b‐3p may become a promising biomarker for CRC metastasis.