Mitochondrial Respiratory Defect Enhances Hepatoma Cell Invasiveness via STAT3/NFE2L1/STX12 Axis

SIMPLE SUMMARY: Mitochondria are essential organelles responsible for aerobic ATP production in eukaryotes. However, many solid tumor cells harbor an impaired mitochondrial ATP production system: oxidative phosphorylation (OXPHOS). The aim of this study was to elucidate the involvement of the mitochondrial OXPHOS defect in cancer cell activity, especially focusing on hepatoma cell invasiveness. We demonstrated that NADH:Ubiquinone Oxidoreductase Subunit A9 (NDUFA9) depletion was an upstream driver of the OXPHOS defect and nuclear factor-erythroid 2 like 1 (NFE2L1) upregulation in HCC tumors. NFE2L1 is the key transcription factor to enhance hepatoma cell invasiveness via STX12 expression. Our study presents a novel mitochondrial dysfunction-mediated retrograde signaling pathway and the resulting transcriptomic reprogramming in liver cancer progression, providing the NDUFA9/NFE2L1/STX12 axis as a key prognostic marker of aggressive liver cancer with mitochondrial defects. ABSTRACT: Mitochondrial respiratory defects have been implicated in cancer progression and metastasis, but how they control tumor cell aggressiveness remains unclear. Here, we demonstrate that a mitochondrial respiratory defect induces nuclear factor-erythroid 2 like 1 (NFE2L1) expression at the transcriptional level via reactive oxygen species (ROS)-mediated STAT3 activation. We identified syntaxin 12 (STX12) as an effective downstream target of NFE2L1 by performing cDNA microarray analysis after the overexpression and depletion of NFE2L1 in hepatoma cells. Bioinformatics analysis of The Cancer Genome Atlas Liver Hepatocellular carcinoma (TCGA-LIHC) open database (n = 371) also revealed a significant positive association (r = 0.3, p = 2.49 × 10(−9)) between NFE2L1 and STX12 expression. We further demonstrated that STX12 is upregulated through the ROS/STAT3/NFE2L1 axis and is a key downstream effector of NFE2L1 in modulating hepatoma cell invasiveness. In addition, gene enrichment analysis of TCGA-LIHC also showed that epithelial–mesenchymal transition (EMT)-related core genes are significantly upregulated in tumors co-expressing NFE2L1 and STX12. The positive association between NFE2L1 and STX12 expression was validated by immunohistochemistry of the hepatocellular carcinoma tissue array. Finally, higher EMT gene enrichment and worse overall survival (p = 0.043) were observed in the NFE2L1 and STX12 co-expression group with mitochondrial defect, as indicated by low NDUFA9 expression. Collectively, our results indicate that NFE2L1 is a key mitochondrial retrograde signaling-mediated primary gene product enhancing hepatoma cell invasiveness via STX12 expression and promoting liver cancer progression.