S100A9 promotes tumor-associated macrophage for M2 macrophage polarization to drive human liver cancer progression: An in vitro study

Tumor-associated macrophages (TAMs) and M2 macrophage polarization have been documented for their implication in various malignancies, but their implication in liver cancer remains to be determined. This study is intended to explore the effect of S100A9 regulated TAMs and macrophage polarization in liver cancer progression. THP-1 cells were induced to differentiate into M1 and M2 macrophages, which were then cultured in liver cancer cell conditioned culture medium before the M1 and M2 macrophages were identified by measuring biomarkers using real-time polymerase chain reaction. The differential expressed genes in macrophages in Gene Expression Omnibus (GEO) databases were screened. S100A9 overexpression and knockdown plasmid were transfected into macrophages to determine the effect of S100A9 on M2 macrophage polarization of TAMs and on proliferation ability of liver cancer cells. The proliferation, migration, invasion, and epithelial-mesenchymal transition (EMT) abilities of liver cancer co-cultured with TAMs. M1 and M2 macrophages were successfully induced and liver cancer cell conditioned culture medium can increase polarization of macrophages into M2 macrophages, in which elevated expression of S100A9 was detected. Data in GEO database showed that tumor microenvironment (TME) upregulated S1000A9 expression. Suppression on S1000A9 can significantly suppress M2 macrophage polarization. TAM can provide the necessary microenvironment for liver cancer cells, HepG2 and MHCC97H by increasing cell proliferation, migration, and invasion ability, while suppression on S1000A9 can reverse this expression pattern. Suppression on S100A9 expression can regulate M2 macrophage polarization of TAMs to suppress the progression of liver cancer.