TGFB1 and hepatocellular carcinoma: Importantly, TGF-β gene and protein expression were elevated without alteration of HIF-1α heterodimer partner, ARNT, and HIF-1α hydroxylase, PHD2 protein levels under hypoxia in HCC cells (Figs. 1b, c and S1a), suggesting hypoxia promoted TGF-β signaling.