Involvement of glypican-3 in the recruitment of M2-polarized tumor-associated macrophages in hepatocellular carcinoma

Previously, we demonstrated that membrane expression of glypican-3 (GPC3) stimulates the recruitment of macrophages into human hepatocellular carcinoma (HCC) tissues. However, functional polarization of the macrophages and the chemoattractant factors related to the recruitment has yet to be determined. In this study, to clarify the polarization (M1 or M2) of the macrophages and provide a clue as to the factors involved in the recruitment, we used xenograft models of SK-HEP-1 and SK03 cell lines with undetectable and high-level membrane expression of GPC3, respectively and analyzed the expression profiles of the relevant genes in both xenografts mainly using microarray techniques. Clustering analyses with mouse genome arrays revealed that the SK-HEP-1 and SK03 xenografts showed different expression profiles for M2 macrophage-related genes but not for M1 macrophage-related genes. Many of the M2 macrophage-related genes were upregulated in the SK03 xenografts compared to the SK-HEP-1 xenografts. Additionally, most of the macrophages infiltrating into the SK03 xenografts were positive for M2 macrophage-specific markers. Regarding the chemoattractant factors, the microarray and quantitative real-time PCR analyses revealed that, of the genes reportedly related to macrophage recruitment, CCL5, CCL3 and CSF1 were significantly upregulated in the SK03 xenograft. These findings suggest that the macrophages recruited into GPC3-overexpressing (with membrane expression) HCC are M2-polarized ones and, more specifically, M2 tumor-associated macrophages which are known to promote tumor progression and metastasis, and CCL5, CCL3 and CSF1 are possible candidate genes for the recruitment of macrophages.