Transforming growth factor β-interacting factor-induced malignant progression of hepatocellular carcinoma cells depends on superoxide production from Nox4.

Hepatocellular carcinoma (HCC) is one of the most deadly malignancies worldwide because of its high recurrence rate, high metastatic potential, and resistance to drugs. Elucidation of the mechanisms underlying malignancy in HCC is needed to improve diagnosis, therapy, and prognosis. Previously, we showed that transforming growth factor β-interacting factor (TGIF) antagonizes arsenic trioxide-induced apoptosis of HepG2 cells and is associated with poor prognosis and progression of urothelial carcinoma in patients after radical nephroureterectomy. To determine whether TGIF plays a role in HCC tumorigenesis, we compared the expression of TGIF, its downstream targets, and reactive oxygen species levels between HCC HepG2 cells and the more invasive SK-Hep1 cells. Superoxide production, phosphorylation of c-Src(Y416) and AKT(S473), and expression of TGIF and NADPH oxidase (Nox) were higher in invasive SK-Hep1 cells than in HepG2 cells. TGIF-overexpressing HepG2 xenograft tumors markedly promoted tumor growth and metastasis to the lungs. Overexpression of TGIF in HepG2 cells increased superoxide production from Nox4, matrix metalloproteinase expression, invadopodia formation, and cellular migration/invasion ability. Conversely, knockdown of TGIF in SK-Hep1 cells attenuated these processes. Using gene knockdown and pharmacological inhibitors, we demonstrate that c-Src/AKT is the upstream signaling that regulates TGIF-induced Nox4 activation and subsequent superoxide production. Taken together, our results implicate TGIF as a potential biomarker for prognosis and target for clinical therapy in patients with advanced HCC.