Neighboring macrophage-induced alteration in the phenotype of colorectal cancer cells in the tumor budding area

Abstract

Background A higher number of tumor buds in the invasive front of colorectal cancer (CRC) specimens has been shown to contribute to a poor prognosis in CRC patients. Because macrophages (Mφs) have been demonstrated to alter the phenotype of cancer cells, we hypothesized that the phenotype of CRC cells in the tumor budding (TB) area might be changed by the interaction between CRC cells and Mφs. Methods We assessed the expression of topoisomerase 1 in CRC cells to estimate the acquisition of chemoresistance in CRC. To demonstrate the tumor-stromal interaction between CRC cells and Mφs, we assessed two histological findings, the number of Mφs per single CRC cell and the proximity between CRC cells and Mφs by histological spatial analysis using HALO software. Results The expression levels of topoisomerase 1 in CRC cells were decreased in deeper areas, especially in the TB area, compared to the surface area. Our histological spatial analysis revealed that approximately 2.6 Mφs located within 50 µm of a single CRC cell were required to alter the phenotype of the CRC cell. Double-immunofluorescence staining revealed that many CD68+ Mφs were positive for interleukin-6 (IL-6) in the TB area and that AE1/AE3-positive CRC cells in the TB area were positive for phospho-STAT3 (pSTAT3); thus, the IL-6 receptor (IL-6R)/STAT3 signaling pathway in CRC cells was upregulated by IL-6 derived from neighboring Mφs. Conclusions The phenotype of CRC cells in the TB area is altered by neighboring Mφs via the IL-6R/STAT3 signaling pathway.