Mitochondrial Ca signaling, which is strongly dependent on the mitochondrial Ca uniporter (MCU) complex, has a series of key roles in physiopathological processes, including energy metabolism, reactive oxygen species (ROS) production and cell apoptosis. However, a mechanistic understanding of how the mitochondrial Ca signaling is remodeled and its functional roles remains greatly limited in cancers, especially in hepatocellular carcinoma. Here we demonstrated that the MCU complex was dysregulated in hepatocellular carcinoma (HCC) cells and significantly correlated with metastasis and poor prognosis of HCC patients. Upregulation of MCU clearly enhanced the Ca uptake into mitochondria, which significantly promoted ROS production by downregulating nicotinamide adenine dinucleotide (NAD)/reduced form of nicotinamide adenine dinucleotid (NADH) ratio and the NAD-dependent deacetylase activity of sirtuin 3 to inhibit superoxide dismutase 2 (SOD2) activity. Moreover, our data indicated that the MCU-dependent mitochondrial Ca uptake promotes matrix metalloproteinase-2 activity and cell motility by ROS-activated c-Jun N-terminal kinase pathway, and thus contributed to the increased ability of invasion and migration in vitro and intrahepatic and distal lung metastasis in vivo of HCC cells. In addition, treatment with the mitochondrial Ca-buffering protein parvalbumin significantly suppressed ROS production and the ability of HCC metastasis. Our study uncovers a mechanism that links the remodeling of mitochondrial Ca homeostasis to ROS production, and provides evidence supporting a metastasis-promoting role for the MCU-dependent mitochondrial Ca uptake in HCC. Our findings suggest that the mitochondrial Ca uptake machinery may potentially be a novel therapeutic target for HCC metastasis.

In a previous study, we elucidated the specific microRNA (miRNA) profile of hepatic differentiation. In this study, we aimed to clarify the instructive role of six overexpressed miRNAs (miR-1246, miR-1290, miR-148a, miR-30a, miR-424 and miR-542-5p) during hepatic differentiation of human umbilical cord lining-derived mesenchymal stem cells (hMSCs) and to test whether overexpression of any of these miRNAs is sufficient to induce differentiation of the hMSCs into hepatocyte-like cells. Before hepatic differentiation, hMSCs were infected with a lentivirus containing a miRNA inhibitor sequence. We found that downregulation of any one of the six hepatic differentiation-specific miRNAs can inhibit HGF-induced hepatic differentiation including albumin expression and LDL uptake. Although overexpression of any one of the six miRNAs alone or liver-enriched miR-122 cannot initiate hepatic differentiation, ectopic overexpression of seven miRNAs (miR-1246, miR-1290, miR-148a, miR-30a, miR-424, miR-542-5p and miR-122) together can stimulate hMSC conversion into functionally mature induced hepatocytes (iHep). Additionally, after transplantation of the iHep cells into mice with CCL4-induced liver injury, we found that iHep not only can improve liver function but it also can restore injured livers. The findings from this study indicate that miRNAs have the capability of directly converting hMSCs to a hepatocyte phenotype in vitro.

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