High expression of peroxisomal D-bifunctional protein in cytosol regulates apoptosis and energy metabolism of hepatocellular carcinoma cells via PI3K/AKT pathway.

Peroxisomal D-bifunctional protein (DBP) is an indispensable enzyme of the fatty acid β-oxidation in the peroxisome of humans. However, the role of DBP in oncogenesis is poorly understood. Our previous studies have demonstrated that DBP overexpression promotes hepatocellular carcinoma (HCC) cell proliferation. In this study, we evaluated the expression of DBP in 75 primary HCC samples using RT-qPCR, immunohistochemistry, and Western blot, as well as its correlation with the prognosis of HCC. In addition, we explored the mechanisms by which DBP promotes HCC cell proliferation. We found that DBP expression was upregulated in HCC tumor tissues, and higher DBP expression was positively correlated with tumor size and TNM stage. Multinomial ordinal logistic regression analysis indicated that lower DBP mRNA level was an independent protective factor of HCC. Notably, DBP was overexpressed in the peroxisome and cytosol and mitochondria of tumor tissue cells. Xenograft tumor growth was promoted by overexpressing DBP outside peroxisome in vivo. Mechanistically, DBP overexpression in cytosol activated the PI3K/AKT signaling axis and promoted HCC cell proliferation by downregulating apoptosis via AKT/FOXO3a/Bim axis. In addition, overexpression of DBP increased glucose uptake and glycogen content via AKT/GSK3β axis, as well as elevated the activity of mitochondrial respiratory chain complex III to increase ATP content via the mitochondrial translocation of p-GSK3β in an AKT-dependent manner. Taken together, this study was the first to report the expression of DBP in peroxisome and cytosol, and that the cytosolic DBP has a critical role in the metabolic reprogramming and adaptation of HCC cells, which provides a valuable reference for instituting an HCC treatment plan.