Fig. 6

PIWIL1-induced Complement C3 expression in HCC cells regulated the immunosuppressive activity of HCC. a Gene lists in two enriched clusters, immune system regulation, and lipid metabolism regulation were overlapped. Complement C3 was the only common gene in both clusters; b the secretion of complement C3 was measured in wild type and PIWIL1-overexpressing HCC cells, which showed that PIWIL1 overexpression could remarkably induce C3 secretion in HCC cells; c Complement C3 level was also then measured in the circulating blood and surrounding hepatic tissues of mice with wild type or PIWIL1-overexpressing HCC. Increased complement C3 level in surrounding hepatic tissues but not circulating blood of mice with PIWIL1-overexpressing HCC was observed. The BMDMs were isolated using ficoll method, and cultured with 50% conditioned medium from PIWIL1-overexpressing HCC cells for 4 days in the presence of neutralizing antibodies against human complement C3 protein. Blockade of Complement C3 significantly reduced d the activation of p38 MAPK and e secretion of IL10; A stable C3 knockdown clone of PIWIL1-overexpressing MHCC97L cells was constructed. The orthotopic HCC model was established with PIWIL1-overexpressing tumor cells with or without C3 knockdown. Knockdown of C3 in PIWIL1-overexpressing HCC cells could significantly attenuate f growth rate, g tumor size of PIWIL1-overexpressing HCC in mice, and h potently suppress the infiltration and accumulation of PMN-MDSCs at the hepatic tissue surrounding PIWIL1-overexpressing HCC tumors (n = 5). All experiments were performed in triplicate if without particular notice. *p < 0.05; **p < 0.01; ***p < 0.001