Infiltrating regulatory T cells promote invasiveness of liver cancer cells via inducing epithelial-mesenchymal transition

BACKGROUND: Regulatory T (Treg) cells are a major component of the microenvironment of hepatocellular carcinoma (HCC) contributing to immunosuppression. The present study aimed to evaluate the effects of Treg cells on the invasion potential of HCC. METHODS: Infiltrating Treg cells were isolated from fresh HCC tissues by immunomagnetic bead separation and detected by flow cytometry. Circulating tumor cells (CTCs) were detected using the CellSearch platform. The cell migration and invasion potentials were evaluated by Transwell assays. The cell viability was tested by the cell counting kit-8 (CCK8) approach, and the apoptosis rates were determined by flow cytometry. The concentrations of active transforming growth factor-β1 (TGFβ1) were measured by enzyme-linked immunosorbent assay. RESULTS: Infiltrating Treg cells significantly correlated with the number of CTCs and vascular invasion (both P<0.05). Moreover, these cells could greatly promote HCC migration, invasion, and proliferation, and inhibit HCC apoptosis. Polymerase chain reaction and Western blot assays revealed that Treg cells significantly decreased the expression levels of epithelium-related molecules and increased the expression levels of mesenchyme-related molecules. Treg cells could activate Smad2/3 via secreting TGFβ1, and these effects could be impaired by knocking down the expression of TGFβ1 in Treg cells. CONCLUSIONS: The involvement of infiltrating Treg cells in triggering the TGFβ1 signaling pathway and promoting the epithelial-mesenchymal transition (EMT) of cancer cells during tumor hematogenous dissemination is presumably responsible for increasing the invasiveness potential of HCC cells. Targeting Treg cells in microenvironments can be a promising therapeutic strategy to improve the prognosis for patients with HCC undergoing resection.