Otakhor Kelly O, Zaidi Mohd Ali Abbas, Oberley-Deegan Rebecca, Ponnusamy Moorthy, Schott Micah B
Department of Molecular Genetics and Cell Biology, University of Nebraska Medical Center, Omaha, NE.
Department of Biochemistry and Molecular Biology, University of Nebraska Medical Center, Omaha, NE.
bioRxiv. 2025 Aug 24:2025.08.20.670915. doi: 10.1101/2025.08.20.670915.
Altered lipid metabolism and lipid droplet (LD) dynamics are hallmark features of hepatocellular carcinoma (HCC) subtypes, but the molecular mechanisms governing LD trafficking and catabolism in HCC cells remain unclear. The small GTPase Rab5, a key regulator of early endosomal dynamics, has been observed to localize to the surface of LDs, suggesting it may play a role in LD turnover. However, the regulation of Rab5-LD interactions and its functional consequences in HCC cell metabolism and proliferation have not been elucidated. In this study, we explored the role of Rab5 in governing LD homeostasis and its impact on HCC cell proliferation. We found that the GTP-bound (Q79L), active form of Rab5 exhibited increased association with LDs compared to the GDP-bound, inactive mutant (S34N). Nutrient starvation enhanced Rab5 GTP-loading and its recruitment to LDs, indicating that Rab5's GTPase cycle regulates its LD localization. Importantly, inhibition of Rab5 GTP-binding impaired LD catabolism, reduced mitochondrial oxidative phosphorylation, and significantly impaired HCC cell proliferation. Transcriptomic analyses further revealed that RAB5 is significantly overexpressed in HCC patient samples, and this overexpression correlated with poorer overall survival. These findings demonstrate that Rab5's GTPase cycle is a critical regulator of LD dynamics in HCC cells, governing LD turnover to sustain mitochondrial energy production and support cancer cell proliferation. Targeting the Rab5-mediated regulation of LD metabolism may represent a novel therapeutic strategy to disrupt the metabolic adaptations that fuel liver cancer progression.
脂质代谢改变和脂滴（LD）动态变化是肝细胞癌（HCC）亚型的标志性特征，但肝细胞癌细胞中调控LD转运和分解代谢的分子机制仍不清楚。小GTP酶Rab5是早期内体动态变化的关键调节因子，已观察到它定位于LD表面，提示其可能在LD周转中发挥作用。然而，Rab5与LD相互作用的调控及其在HCC细胞代谢和增殖中的功能后果尚未阐明。在本研究中，我们探讨了Rab5在调控LD稳态中的作用及其对HCC细胞增殖的影响。我们发现，与结合GDP的无活性突变体（S34N）相比，结合GTP的（Q79L）活性形式的Rab5与LD的结合增加。营养饥饿增强了Rab5的GTP负载及其向LD的募集，表明Rab5的GTP酶循环调节其在LD上的定位。重要的是，抑制Rab5的GTP结合会损害LD分解代谢，降低线粒体氧化磷酸化，并显著损害HCC细胞增殖。转录组分析进一步显示，RAB5在HCC患者样本中显著过表达，且这种过表达与较差的总生存期相关。这些发现表明，Rab5的GTP酶循环是HCC细胞中LD动态变化的关键调节因子，控制LD周转以维持线粒体能量产生并支持癌细胞增殖。靶向Rab5介导的LD代谢调节可能代表一种破坏促进肝癌进展的代谢适应的新治疗策略。
