Metallothionein 1 family profiling identifies MT1X as a tumor suppressor involved in the progression and metastastatic capacity of hepatocellular carcinoma

Metallothionein 1 (MT1s) is a family of cysteine-rich proteins with diverse functions such as metal homeostasis, oxidative stress, and carcinogenesis. However, its involvement in hepatocellular carcinoma (HCC) remains not fully understood. We aimed to explore the contribution of the individual member of MT1s to HCC. Its member mRNA levels were determined in cohort 1 of normal (n=30), cirrhotic (n=30), peritumoral (n=135), and HCC (n=135). In cohort 1, seven of eight members were down-regulated during the transition from normal liver to HCC, and only MT1G and MT1X were correlated with tumor features and outcomes. The MT1X was selected to be further stained in cohort 2 consisting of a series of liver nodules (15 normal livers, 33 cirrhotic livers, 12 dysplastic nodules, 31 HCC, and 9 HCC metastasis), and in cohort 3 (HCC, n=85). In cohort 2, MT1X immunoreactivity was reduced in HCC and lost in metastatic HCC and showed good diagnostic performance for HCC (AUC=0.754, 95%IC=0.659-0.849). In cohort 3, MT1X expression in peritumoral tissues was independent predictor for HCC (recurrence free survival: HR=0.34, 95%CI=0.17-0.66; overall survival: HR=0.32, 95%CI=0.16-0.60). Moreover, we found that ectopic overexpression of MT1X delayed G1/S progression of cell cycle and promoted apoptosis in HCC cells in vitro, and suppressed tumor growth and lung metastasis in nude mice in vivo. We further demonstrated that MT1X induces cell cycle arrest and apoptosis by inactivating NF-B signaling in HCC. In conclusion, MT1X may serve as a candidate of prognostic indicator and inhibits the progression and metastasis of HCC.