Cholesterol trafficking is required for mTOR activation in endothelial cells

Department of Pharmacology and Oncology, The Johns Hopkins School of Medicine, Baltimore, MD 21205, USA.
Proceedings of the National Academy of Sciences (Impact Factor: 9.81). 02/2010; 107(10):4764-9. DOI: 10.1073/pnas.0910872107
Source: PubMed

ABSTRACT Mammalian target of rapamycin (mTOR) constitutes a nodal point of a signaling network that regulates cell growth and proliferation in response to various environmental cues ranging from growth factor stimulation to nutrients to stress. Whether mTOR is also affected by cholesterol homeostasis, however, has remained unknown. We report that blockade of cholesterol trafficking through lysosome by a newly identified inhibitor of angiogenesis, itraconazole, leads to inhibition of mTOR activity in endothelial cells. Inhibition of mTOR by itraconazole but not rapamycin can be partially restored by extracellular cholesterol delivered by cyclodextrin. Moreover, other known inhibitors of endosomal/lysosomal cholesterol trafficking as well as siRNA knockdown of Niemann-Pick disease type C (NPC) 1 and NPC2 also cause inhibition of mTOR in endothelial cells. In addition, both the accumulation of cholesterol in the lysosome and inhibition of mTOR caused by itraconazole can be reversed by thapsigarin. These observations suggest that mTOR is likely to be involved in sensing membrane sterol concentrations in endothelial cells, and the cholesterol trafficking pathway is a promising target for the discovery of inhibitors of angiogenesis.

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    • "The antiangiogenic activity of ITZ has been attributed at least in part to its inhibition of the mTOR signaling pathway through disruption of the shuttling of cholesterol between plasma membrane and late endosomes/lysosomes, thereby inducing the accumulation of cholesterol in the endolysosomal system (Xu et al., 2010). We found that cholesterol, stained with filipin, was redistributed not only by ITZ and posaconazole but also by ketoconazole (which does not inhibit virus replication) in two human cell lines (HAP1 [Figure 2C] and HeLa R19 cells [Figure S3E]). "
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    • "Processes depicted have been observed in a number of LSDs but do not necessarily apply to all LSDs. human umbilical vein endothelial cells (Xu et al., 2010), and in MCOLN1-deficient Drosophila pupae (Wong et al., 2012), but not in brain samples from Sandhoff, GM1-gangliosidosis, and NPC1 mice (Boland et al., 2010). Considering the myriad of cellular signaling pathways that mTOR is involved in (Laplante and Sabatini, 2012), it may be necessary to differentiate mTOR activity in affected cell populations of different brain regions. "
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