Abstract.Previous studies have shown that S100 calcium-binding protein A8 (S100A8) contributes to the survival and migration of colorectal cancer (CRC) cells. However, whether S100A8 participates in the progression and metastasis of CRC via the regulation of macrophages in the tumor inflammatory microenvironment remains unknown. In this study, phorbol myristate acetate (PMA) was used to induce the differentiation of THP-1 monocytes to macrophages. MTT assay, western blot analysis, immunofluorescence staining, semi-quantitative RT-PCR (semi-PCR), quantitative real-time PCR (qPCR), Gaussia luciferase activity assay and ELISA were performed to analyze the roles and molecular mechanisms of S100A8 in the modulation of macrophages. MTT assay, flow cytometric analysis, Hoechst staining, wound healing and Transwell migration assay were used to test the effect of S100A8 on the viability and migration of CRC cells co-cultured with macrophages in the inflammatory microenvironment. We found that THP-1 monocytes were induced by PMA and differentiated to macrophages. S100A8 activated the NF-κB pathway in the macrophages and promoted the expression of miR-155 and inflammatory cytokines IL-1β and TNF-α in the inflammatory microenvironment mimicked by lipopolysaccharides (LPS). Furthermore, S100A8 contributed to augment the migration but not the viability of the CRC cells co-cultured with the macrophages in the inflammatory microenvironment. Altogether, our study demonstrated that S100A8 facilitated the migration of CRC cells in the inflammatory microenvironment, and the underlying molecular mechanisms may be partially attributed to the overexpression of miR-155, IL-1β and TNF-α through activation of the NF-κB pathway in macrophages.
IntroductionColorectal cancer (CRC), for which distant metastasis accounts for the leading cause of cancer mortality, is one of the most malignant gastrointestinal carcinomas worldwide (1). The pathogenesis of CRC is a complex process and involves environmental influences, genetic alterations, and the host immune system and their interactions. The formation of an inflammatory microenvironment also plays a pivotal role in the development of CRC (2). The host microenvironment is comprised of numerous infiltrating immune cell types and resident tumor cells. Among the immune cells, macrophages play an indispensable role. For instance, macrophage infiltration in colon tissue has been observed in both inflammatory bowel disease (IBD) and CRC (4), and the cytokines secreted by macrophages under certain conditions have directly or indirectly stimulated inflammation and tumor progression (5,6). Although great progress has been made, the interactions and the molecular mechanisms between CRC and the inflammatory microenvironment remain unknown. S100A8 (calgranulin A or S100 calcium-binding protein A8) is a member of the low-molecular calcium binding S100 protein family. It also belongs to the family of damage-associated molecular patterns (DAMPs). Studies have shown that S100A8 plays an important role in regul...