Stanniocalcin 2 (STC2) is a potent biomarker of hepatocellular carcinoma with its expression being augmented in Nrf1α-deficient cells, but diminished in Nrf2-deficient cells

For insights into the fact that liver-specific knockout of Nrf1 leads to development of non-alcoholic steatohepatitis and spontaneous hepatoma, we previously found that loss of Nrf1 (i.e., a full-length isoform encoded by Nfe2l1) promotes HepG2-derived tumor growth in xenograft mice, but malgrowth of the xenograft tumor is significantly suppressed by knockout of Nrf2 (encoded by Nfe2l2). The mechanism underlying such marked distinctions in their pathologic phenotypes remains elusive, however, to date. Herein, we mined the transcriptome data of liver cancer from the TCGA database to establish a prognostic model of liver cancer and then calculated the predicted risk score of each cell line. The results indicated that knockout of Nrf1 significantly increased the risk score in HepG2 cells, whereas the risk score was reduced by knockout of Nrf2. Of note, stanniocalcin 2 (STC2, a biomarker of liver cancer, that is up-expressed in hepatocellular carcinoma (HCC) tissues with a reduction in the overall survival ratio of those patients) was augmented in Nrf1Nrf2-/- cells, but diminished in Nrf2-/- cells. Thereby, it is inferable that STC2 is likely involved in mediating the distinction between Nrf1Nrf2-/- and Nrf2-/-. Further investigation revealed that HIF1A is an upstream regulator of STC2 in caNrf2{Delta}N, rather than Nrf1Nrf2-/-, cells, and regulation of STC2 and HIF1A in Nrf1Nrf2-/- is determined by Nrf2, but the regulation of STC2 by Nrf2 may be independent on HIF1A. In turn, STC2 can regulate Nrf2 via the putative calcium-mediated Keap1-p62 signaling so to form a feedback regulatory loop. Such potential function of STC2 was further corroborated by a series of experiments combined with transcriptomic sequencing. The results unraveled that STC2 manifests as a dominant tumor-promoter, because the STC2-leading increases in clonogenicity of hepatoma cells and malgrowth of relevant xenograft tumor were almost completely abolished in STC2-/-cells. Together, these demonstrate that STC2 could be paved as a novel potent therapeutic target, albeit as a diagnostic marker, for hepatocellular carcinoma.