Presence of Membrane-Bound TGF-β1 and Its Regulation by IL-2-Activated Immune Cell-Derived IFN-γ in Head and Neck Squamous Cell Carcinoma Cell Lines

Abstract

The presence of membrane-bound TGF-beta1 (mTGF-beta1) has been recently observed in regulatory T cells, but only a few studies have reported the same phenomenon in cancer cells. In this study, we investigate the regulation of mTGF-beta1 expression in five head and neck squamous cell carcinoma cell lines using FACS analysis. Through blocking Ab and exogenous cytokine treatment experiments, we found that expression of mTGF-beta1 is significantly induced by the activated immune cell-derived factor IFN-gamma. In addition, IFN-gamma and TNF-alpha are shown to have a synergistic effect on mTGF-beta1 expression. Moreover, we found that exogenous TNF-alpha induces endogenous TNF-alpha mRNA expression in an autocrine loop. In contrast to previous reports, we confirm that, in this model, mTGF-beta1 is neither a rebound form of once-secreted TGF-beta1 nor an activated form of its precursor membrane latency-associated peptide. Inhibitors of transcription (actinomycin D), translation (cycloheximide), or membrane translocation (brefeldin A) effectively block the induction of mTGF-beta1, which suggests that induction of mTGF-beta1 by IFN-gamma and/or TNF-alpha occurs through de novo synthesis. These findings suggest that some cancer cells can detect immune activating cytokines, such as IFN-gamma and TNF-alpha, and actively block antitumor immunity by induction of mTGF-beta1.