GSTK1 suppresses HCC aggravation via L-carnitine metabolism by PGAM5/DRP1 complex-mediated mitochondrial quality control.

BACKGROUND: Hepatocellular carcinoma (HCC) is among the leading causes of cancer-related mortality worldwide. The high recurrence rate and resistance to chemotherapy of HCC contribute to poor clinical outcomes, necessitating the development of novel therapeutic strategies. Glutathione S-transferase kappa 1 (GSTK1) is specifically localized to mitochondria and peroxisomes, participates in adiponectin secretion and insulin resistance, and inhibits the progression of non-alcoholic fatty liver disease. However, the role of GSTK1 in HCC is unknown. We aimed to determine the role of GSTK1 in HCC progression. METHODS: N-nitrosodiethylamine (DEN)/ carbon tetrachloride and DEN/high-fat, high-fructose, high-cholesterol diet models were used in hepatocyte-specific Gstk1 knockout and control mice to establish a murine HCC model. Human HCC cell lines with GSTK1 overexpression or knockdown were used to determine GSTK1 function in tumor growth and migration in vitro. Non-target metabolomics analysis, RNA-sequence, transmission electron microscope (TEM), immunoprecipitation (IP), liquid chromatography, and high-throughput mass spectrometry (LC-MS/MS) were used to determine the mechanism by which GSTK1 participates in HCC. RESULTS: GSTK1 was shown to suppress HCC in vivo and in vitro. Non-target metabolomics analysis indicated that GSTK1 participates in L-carnitine metabolism. L-carnitine supplementation inhibited proliferation and promoted apoptosis of HCC cells in vivo and in vitro. This effect was enhanced by GSTK1 overexpression. Mechanically, TEM and western blot showed that GSTK1 influences mitochondrial quality control (MQC) by promoting mitochondrial biosynthesis and mitochondrial fusion. GSTK1 was shown to inhibit mitochondrial fission and mitophagy, which was consistent with the immunofluorescence results. IP and LC-MS/LMS indicated that GSTK1 combines with PGAM5 and competes with DRP1. Additionally, GSTK1 was shown to be regulated by transcription factors (PPARα/RXRα) and the RXRα agonist, bexarotene, inhibited HCC cell proliferation. CONCLUSIONS: GSTK1 was shown to be a tumor suppressor via its role in MQC and L-carnitine metabolism. Bexarotene and L-carnitine supplementation may serve as potential therapeutic strategies for HCC treatment.