Cholesterol trafficking is required for mTOR activation in endothelial cells

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.

Effect of a Synthetic Liver X Receptor Agonist TO901317 on Cholesterol Concentration in Goose Primary Hepatocytes

“…Similarly, our study showed that treatment with TO901317 in goose hepatocytes promoted mRNA expression of S6K. Otherwise, one previous study suggested that cholesterol trafficking is required for mTOR activation in endothelial (Xu et al, 2010), which confirmed the role of mTOR in cholesterol biosynthesis. Huwait et al showed that the LXR agonists-induced ABCA1 promoter activity was inhibited by the expression of dominant negative forms of the components of the PI3K pathways (Huwait et al, 2011).…”

Low-density Lipoprotein Receptor Deficiency Causes Impaired Osteoclastogenesis and Increased Bone Mass in Mice because of Defect in Osteoclastic Cell-Cell Fusion

“…Numerous studies have indicated a critical involvement of cholesterol in the differentiation and function of a variety of cell types, including endothelial cells, cardiac muscle cells, macrophages, and osteoblasts (57)(58)(59). It is well known that cholesterol is a major component of the plasma membrane, and especially of lipid rafts (36 -39).…”

Repurposing itraconazole as an anticancer agent

“…Itraconazole inhibits AKT (protein kinase B)/mechanistic target of rapamycin (mTOR) signaling in human umbilical vein endothelial cells (HUVECs), glioblastoma, endometrial carcinoma (EC) and melanoma cells (10)(11)(12)(13)(14). Inhibition of Hedgehog signaling was observed in basal cell carcinoma, medulloblastoma, pleural mesothelioma, breast cancer and melanoma cells (9,(14)(15)(16)(17), but not in EC cells (13).…”