The treatment for hepatocellular carcinoma (HCC) is promising in recent years, but still facing critical challenges. The first targeted therapy, sorafenib, prolonged the overall survival by months. However, resistance often occurs, largely limits its efficacy. Sorafenib was found to target the electron transport chain complexes, which results in the generation of reactive oxygen species (ROS). To maintain sorafenib resistance and further facilitate tumor progression, cancer cells develop strategies to overcome excessive ROS production and obtain resistance to oxidative stress-induced cell death. In the present study, we investigated the roles of ROS in sorafenib resistance, and found suppressed ROS levels and reductive redox states in sorafenib-resistant HCC cells. Mitochondria in sorafenib-resistant cells maintained greater functional and morphological integrity under the treatment of sorafenib. However, cellular oxygen consumption rate and mitochondria DNA content analyses revealed fewer numbers of mitochondria in sorafenib-resistant cells. Further investigation attributed this finding to decreased mitochondrial biogenesis, likely caused by the accelerated degradation of peroxisome proliferator-activated receptor γ coactivator 1β (PGC1β). Mechanistic dissection showed that upregulated UBQLN1 induced PGC1β degradation in a ubiquitination-independent manner to attenuate mitochondrial biogenesis and ROS production in sorafenib-resistant cells under sorafenib treatment. Furthermore, clinical investigations further indicated that the patients with higher UBQLN1 levels experienced worse recurrence-free survival. In conclusion, we propose a novel mechanism involving mitochondrial biogenesis and ROS homeostasis in sorafenib resistance, which may offer new therapeutic targets and strategies for HCC patients.

Sorafenib resistance is a major obstacle to the treatment of advanced hepatocellular carcinoma (HCC). MicroRNAs (miRNAs) are multifunctional regulators of gene expression with profound impact for human disease. Therefore, better understanding of the biological mechanisms of abnormally expressed miRNAs is critical to discovering novel, promising therapeutic targets for HCC treatment. This study aimed to investigate the role of miR-378a-3p in the sorafenib resistance of HCC and elucidate the underlying molecular mechanisms. Methods : A novel hub miR-378a-3p was identified based on miRNA microarray and bioinformatics analysis. The abnormal expression of miR-378-3p was validated in different HCC patient cohorts and sorafenib-resistant (SR) HCC cell lines. The functional role of miR-378a-3p and its downstream and upstream regulatory machinery were investigated by gain-of-function and loss-of-function assays in vitro and in vivo . Interactions among miR-378a-3p, LXRα, and IGF1R were examined by a series of molecular biology experiments. Then, the clinical relevance of miR-378a-3p and its targets were evaluated in HCC samples. HCC patient-derived xenograft (PDX) model was used to assess the therapeutic value of LXRα and its downstream miR-378a-3p. Results : miR-378a-3p expression was frequently reduced in established sorafenib-resistant HCC cell lines. The decreased miR-378a-3p levels correlated with poor overall survival of HCC patients following sorafenib treatment. miR-378a-3p overexpression induced apoptosis in SR HCC cells, whereas miR-378a-3p silencing exerted the opposite effects. IGF1R was identified as a novel target of miR-378a-3p. Furthermore, the primary miR-378 level was not consistent with its precursor miRNA level in SR HCC cells, which was attributed to the downregulation of exportin5 (XPO5) and subsequently reduced nuclear export of precursor miR-378 and restrained maturation of miR-378-3p. In this context, we combined an agonist GW3965 of liver X receptor alpha (LXRα), which functioned as a transcription activator of miRNA-378a, and its activation re-sensitized sorafenib-resistant cells to sorafenib treatment in vitro and in vivo . Conclusions : Our finding suggested decreased expression of XPO5 prevents maturation of miR-378a-3p, which leaded to the overexpression of IGF-1R and counteracted the effects of sorafenib-induced apoptosis. LXRα was able to activate miRNA-378a-3p transcription in HCC cells and could be a potential combinable treatment strategy with sorafenib to suppress HCC progression.