Department of Radiation Oncology, The Ohio State University Comprehensive Cancer Center, Columbus, Ohio.
Department of Radiation Oncology, Stanford University, Stanford, California.
Mol Cancer Res. 2019 Oct;17(10):2089-2101. doi: 10.1158/1541-7786.MCR-18-1343. Epub 2019 Jul 15.
Accumulation of lipid droplets has been observed in an increasing range of tumors. However, the molecular determinants of this phenotype and the impact of the tumor microenvironment on lipid droplet dynamics are not well defined. The hypoxia-inducible and lipid droplet associated protein HILPDA is known to regulate lipid storage and physiologic responses to feeding conditions in mice, and was recently shown to promote hypoxic lipid droplet formation through inhibition of the rate-limiting lipase adipose triglyceride lipase (ATGL). Here, we identify fatty acid loading and nutrient deprivation-induced autophagy as stimuli of HILPDA-dependent lipid droplet growth. Using mouse embryonic fibroblasts and human tumor cells, we found that genetic ablation of HILPDA compromised hypoxia-fatty acid- and starvation-induced lipid droplet formation and triglyceride storage. Nutrient deprivation upregulated HILPDA protein posttranscriptionally by a mechanism requiring autophagic flux and lipid droplet turnover, independent of HIF1 transactivation. Mechanistically, loss of HILPDA led to elevated lipolysis, which could be corrected by inhibition of ATGL. Lipidomic analysis revealed not only quantitative but also qualitative differences in the glycerolipid and phospholipid profile of HILPDA wild-type and knockout cells, indicating additional HILPDA functions affecting lipid metabolism. Deletion studies of HILPDA mutants identified the N-terminal hydrophobic domain as sufficient for targeting to lipid droplets and restoration of triglyceride storage. , HILPDA-ablated cells showed decreased intratumoral triglyceride levels and impaired xenograft tumor growth associated with elevated levels of apoptosis. IMPLICATIONS: Tumor microenvironmental stresses induce changes in lipid droplet dynamics via HILPDA. Regulation of triglyceride hydrolysis is crucial for cell homeostasis and tumor growth.
脂滴的积累在越来越多的肿瘤中都有观察到。然而，这种表型的分子决定因素以及肿瘤微环境对脂滴动力学的影响还没有得到很好的定义。缺氧诱导和与脂滴相关的蛋白 HILPDA 已知可调节小鼠的脂质储存和对喂养条件的生理反应，最近还被证明通过抑制限速脂肪酶脂肪甘油三酯脂肪酶 (ATGL) 来促进缺氧脂滴的形成。在这里，我们确定脂肪酸负荷和营养剥夺诱导的自噬是 HILPDA 依赖性脂滴生长的刺激因素。使用小鼠胚胎成纤维细胞和人类肿瘤细胞，我们发现 HILPDA 的基因缺失会损害缺氧-脂肪酸和饥饿诱导的脂滴形成和甘油三酯储存。营养剥夺通过需要自噬通量和脂滴周转的机制，在后转录水平上调 HILPDA 蛋白，而不依赖于 HIF1 反式激活。从机制上讲，HILPDA 的缺失导致脂解作用升高，这可以通过抑制 ATGL 来纠正。脂质组学分析不仅揭示了 HILPDA 野生型和敲除细胞中甘油磷脂和磷脂的定量差异，还揭示了甘油三酯代谢的其他 HILPDA 功能的定性差异。HILPDA 突变体的缺失研究表明，N 端疏水区足以靶向脂滴并恢复甘油三酯储存。此外，HILPDA 缺失的细胞显示出肿瘤内甘油三酯水平降低，异种移植肿瘤生长受损，与凋亡水平升高相关。意义：肿瘤微环境应激通过 HILPDA 诱导脂滴动力学的变化。甘油三酯水解的调节对于细胞内稳态和肿瘤生长至关重要。
