Fbxw7, a substrate recognition subunit of the SCF ubiquitin ligase complex, regulates the proteasomal degradation of multiple cancer-related and metabolic proteins. To elucidate its role in hepatic lipid homeostasis, we established Fbxw7 knockdown (FKD) Huh-7 cells and analyzed associated morphological and molecular alterations. Lipid droplets were evaluated by BODIPY staining and transmission electron microscopy, while metabolic and autophagy-related factors were examined using immunocytochemistry, Western blotting, and RT-PCR. FKD resulted in marked lipid droplet accumulation and upregulation of lipogenic genes, accompanied by increased levels of both precursor and mature sterol regulatory element-binding protein 1 (SREBP-1) with prominent nuclear localization. In three-dimensional spheroid cultures, FKD cells exhibited extensive vacuolar degeneration, reduced LC3B expression, and p62 accumulation, whereas LAMP-1 expression remained unchanged. Low-vacuum scanning electron microscopy further revealed rough, granular deposits on the spheroid surface, suggesting structural deterioration associated with impaired autophagy. Treatment with the autophagy inducer Tat-Beclin1 partially restored LC3B expression and attenuated lipid droplet accumulation. Collectively, these findings indicate that Fbxw7 plays a critical role in maintaining hepatocellular homeostasis through coordinated regulation of lipid metabolism and autophagic degradation. Loss of Fbxw7 disrupts this balance, leading to characteristic metabolic and morphological alterations in hepatocellular carcinoma cells.
Hayashi et al. (Thu,) studied this question.