Intracellular cholesterol trafficking is dependent upon NPC2 interaction with lysobisphosphatidic acid

Abstract

Unesterified cholesterol accumulation in the late endosomal/lysosomal (LE/LY) compartment is the cellular hallmark of Niemann-Pick C (NPC) disease, caused by defects in the genes encoding NPC1 or NPC2. We previously reported the dramatic stimulation of NPC2 cholesterol transport rates to and from model membranes by the LE/LY phospholipid lysobisphosphatidic acid (LBPA). It had been previously shown that enrichment of NPC1-deficient cells with LBPA results in cholesterol clearance. Here we demonstrate that LBPA enrichment in human NPC2-deficient cells, either directly or via its biosynthetic precursor phosphtidylglycerol (PG), is entirely ineffective, indicating an obligate functional interaction between NPC2 and LBPA in cholesterol trafficking. We further demonstrate that NPC2 interacts directly with LBPA and identify the NPC2 hydrophobic knob domain as the site of interaction. Together these studies reveal a heretofore unknown step of intracellular cholesterol trafficking which is critically dependent upon the interaction of LBPA with functional NPC2 protein.

Bis(monoacylglycero)phosphate, an important actor in the host endocytic machinery hijacked by SARS-CoV-2 and related viruses

“…The cholesterol transfer between NPC2 and membrane vesicles including between inner membranes of the LE/Lys compartment is favored by BMP [ 71 ]. This occurs through the direct interaction of BMP with a domain of NPC2 [ 67 ]. This region is also involved in the interaction between the cytosolic NPC2 and the transmembrane protein NPC1 in the limiting membrane of the LE/Lys.…”

“…Among all cholesterol transport proteins, Niemann-Pick C1 and C2 proteins (NPC1, NPC2) cooperate to regulate the egress of low-density lipoprotein (LDL)-derived cholesterol out of late endosomes [ 67 ]. Other proteins like STARD3 (StAR related lipid transfer domain containing 3) [ 68 ], ORPs (OSPB (Oxysterol Binding proteins)-Related Proteins) [ 69 ] and Aster protein [ 70 ] transport cholesterol between LE, PM, ER, Golgi and mitochondria.…”

“…3 Schematic intracellular lipid flows regulated by sterol transfer proteins and their inhibitors (indicated in red): A) cholesterol efflux from LE/Lys: the cationic amphiphilic drug U18666A binds to NPC1 and inhibits the LDL-derived cholesterol exit from lysosomes thereby inducing NPC phenotype [ 74 , 75 ]. BMP (green conical cylinder) favors the acid hydrolysis of LDL-derived cholesterol ester [ 92 ] and stimulates the rate of cholesterol transfer by NPC2 [ 67 , 71 ]. B) Cholesterol transfer at MCS between ER and Golgi/LE.…”

“…The authors therefore raised the hypothesis that BMP becomes limiting in the NPC disease upon excessive cholesterol overload. Whereas Gruenberg's studies have highlighted a functional crosstalk between BMP and NPC 1/2 proteins, it has been demonstrated that BMP regulates cholesterol transport through direct interaction with NPC2, independent of NPC1 [ 67 ]. Biochemical, structural and atomic scale studies demonstrated that BMP stimulated the extent and rate of cholesterol transfer by NPC2 through direct interaction at the hydrophobic knob domain on the surface of NPC2 [ 67 , 96 ].…”

Cellular endo‐lysosomal dysfunction in the pathogenesis of non‐alcoholic fatty liver disease

“…Although Npc1 affects liver fat metabolism by regulating the transport of lipids and cholesterol from lysosome to different cellular compartments, there are still few evidences for a role of altered Npc1 function in NAFLD pathogenesis. Similar to Npc1, the Npc2 protein also plays an important role in regulating intracellular cholesterol trafficking and homeostasis . Npc2 was downregulated in fatty liver tissues.…”