TGF-β1-mediated repression of SLC7A11 drives vulnerability to GPX4 inhibition in hepatocellular carcinoma cells

System x(c)(-) contributes to glutathione (GSH) synthesis and protects cells against ferroptosis by importing cystine and exchanging it with glutamate. Transforming growth factor beta 1 (TGF-beta 1) induces redox imbalance; however, its role in system x(c)(-) regulation remains poorly understood. The present study was the first to show that TGF-beta 1 repressed the protein and mRNA levels of xCT, a catalytic subunit of system x(c)(-), in PLC/PRF/5, Huh7, Huh6, and HepG2 cells with an early TGF-beta 1 gene signature but not in SNU387, SNU449, SNU475, and SK-Hep1 cells with a late TGF-beta 1 gene signature. TGF-beta 1 treatment for 24 h reduced xCT expression in a dose-dependent manner but this TGF-beta 1-induced repression was blunted by pretreatment with a TGF-beta 1 receptor inhibitor. TGF-beta 1-mediated xCT repression was prevented by Smad3, but not Smad2 or Smad4, knockdown, whereas it was enhanced by Smad3 overexpression. TGF-beta 1 decreased GSH levels in control cells but not xCT-overexpressed cells. Furthermore, TGF-beta 1 increased reactive oxygen species (ROS) levels in PLC/PRF/5 cells and enhanced tert-butyl hydroperoxide-induced ROS levels in Huh7 cells; these changes were reversed by xCT overexpression. TGF-beta 1 treatment ultimately induced the ferrostatin-1- and deferoxamine-dependent lipid peroxidation after 2 days and 8 days in PLC/PRF/5 and Huh7 cells but not in SNU475 and SK-Hep1 cells. Pre-treatment of TGF-beta 1 for 2 days enhanced the reduction of cell viability induced by RSL3, a GSH peroxidase 4 (GPX4) inhibitor, in PLC/PRF/5 and Huh7 cells. In conclusion, TGF-beta 1 represses xCT expression via Smad3 activation and enhances lipid peroxidation in hepatocellular carcinoma cells with an early TGF-beta 1 signature, which would benefit from the targeting of GPX4.