TGF-β1 Secreted by Hepatocellular Carcinoma Induces the Expression of the Foxp3 Gene and Suppresses Antitumor Immunity in the Tumor Microenvironment

Abstract

The purpose of this study was to explore the mechanisms of TGF-β1 mediated immunosuppression in tumor stroma. The expression of TGF-β1 was investigated in Huh7, Hep 3B, SGC-7901, Eca-109 and Hepa1-6 cell lines using immunofluorescence. Knocked-down TGF-β1 of the Hepa1-6 cell line was established through lentivirus-based RNA interference. The interference efficiency of the TGF-β1 gene was tested by real-time PCR and ELISA; the expression of Foxp3, IFN-γ and CD83 in CD4(+), CD8(+) or dendritic cells was examined via flow cytometry; and the tumorigenic ability of the cancer cells was investigated in the animal experiments. The diverse digestive cancer cells were found to secrete TGF-β1, mRNA of which was knocked down by 78 % thanks to lentivirus-based interference in Hepa1-6 cells. Flow cytometry showed that CD4(+)CD25(+)Foxp3(+) regulatory T cells significantly increased in hepatocellular carcinoma patients when compared with those in the healthy controls. The supernatant from Hepa1-6 cells and recombinant TGF-β1 significantly induced the expression of Foxp3 gene in vitro, while that from sh TGF-β1 Hepa1-6 cells restored it. Hepa1-6 cells inhibited IFN-γ and CD83 expression in CD8(+) or dendritic cells by secreting TGF-β1. The animal experiments indicated that the knockdown TGF-β1 gene impaired the tumorigenic ability of Hepa1-6 cells. TGF-β1, expressed in cancer cells, might be a potential therapeutic target for cancer treatment.