ABCG5 and ABCG8 Are Involved in Vitamin K Transport.

ATP-binding cassette protein G5 (ABCG5)/ABCG8 heterodimer exports cholesterol from cells, while Niemann-Pick C1-like 1 (NPC1L1) imports cholesterol and vitamin K. We examined whether ABCG5/ABCG8 transports vitamin K similar to NPC1L1. Since high concentrations of vitamin K show cytotoxicity, the cytoprotective effects of ABCG5/ABCG8 were examined.

ABCA1 and ABCG1 as potential therapeutic targets for the prevention of atherosclerosis.

Prevention of atherosclerosis is important because it is a risk factor for cardiovascular diseases globally. One of the causes of atherosclerosis is accumulation of cholesterol and triglycerides in peripheral cells. ATP-binding cassette protein A1 (ABCA1) and G1 (ABCG1) are important in eliminating excess cholesterol from cells including macrophages and forming high-density lipoprotein, which contributes to the prevention and regression of atherosclerosis.

Niemann-Pick C1-like 1 Promotes Intestinal Absorption of Siphonaxanthin.

Siphonaxanthin is a carotenoid found in certain green algae, and its promising beneficial properties, such as its anti-obesity effect, have recently been demonstrated. However, there is little information about the molecular mechanisms underlying intestinal absorption of siphonaxanthin. In this study, we aimed to elucidate how siphonaxanthin is transported across the intestinal epithelium using differentiated Caco-2 cells (dCaco-2 cells), recombinant proteins, and an animal model.

Phosphorylation by protein kinase C stabilizes ABCG1 and increases cholesterol efflux.

ATP-binding cassette protein G1 (ABCG1) plays an important role in eliminating excess cholesterol from macrophages and in the formation of high-density lipoprotein (HDL), which contributes to the prevention and regression of atherosclerosis. The post-translational regulation of ABCG1 remains elusive, although phosphorylation by protein kinase A destabilizes ABCG1 proteins. We examined the phosphorylation of ABCG1 using HEK293 and Raw264.

The distribution of vinculin to lipid rafts plays an important role in sensing stiffness of extracellular matrix.

Extracellular matrix (ECM) stiffness regulates cell differentiation, survival, and migration. Our previous study has shown that the interaction of the focal adhesion protein vinculin with vinexin α plays a critical role in sensing ECM stiffness and regulating stiffness-dependent cell migration. However, the mechanism how vinculin-vinexin α interaction affects stiffness-dependent cell migration is unclear.

ABCG1 and ABCG4 Suppress γ-Secretase Activity and Amyloid β Production.

ATP-binding cassette G1 (ABCG1) and ABCG4, expressed in neurons and glia in the central nervous system, mediate cholesterol efflux to lipid acceptors. The relationship between cholesterol level in the central nervous system and Alzheimer's disease has been reported. In this study, we examined the effects of ABCG1 and ABCG4 on amyloid precursor protein (APP) processing, the product of which, amyloid β (Aβ), is involved in the pathogenesis of Alzheimer's disease.

Neurite outgrowth stimulation by n-3 and n-6 PUFAs of phospholipids in apoE-containing lipoproteins secreted from glial cells.

PUFAs, which account for 25-30% of the total fatty acids in the human brain, are important for normal brain development and cognitive function. However, it remains unclear how PUFAs are delivered to neurons and exert their effects. In this study, we demonstrated that n-3 and n-6 PUFAs added to the medium are incorporated into membrane phospholipids of primary glial cells from rat cortices, and then secreted as the fatty acid moiety of phospholipids in apoE-containing lipoproteins (LpEs).

ABCB4 exports phosphatidylcholine in a sphingomyelin-dependent manner.

ABCB4, which is specifically expressed on the canalicular membrane of hepatocytes, exports phosphatidylcholine (PC) into bile. Because SM depletion increases cellular PC content and stimulates PC and cholesterol efflux by ABCA1, a key transporter involved in generation of HDL, we predicted that SM depletion also stimulates PC efflux through ABCB4. To test this prediction, we compared the lipid efflux activity of ABCB4 and ABCA1 under SM depletion induced by two different types of inhibitors for SM synthesis, myriocin and (1R,3S)-N-(3-hydroxy-1-hydroxymethyl-3-phenylpropyl)dodecanamide, in human embryonic kidney 293 and baby hamster kidney cells.

Position 834 in TM6 plays an important role in cholesterol and phosphatidylcholine transport by ABCA1.

ATP-binding cassette protein A1 (ABCA1) plays a key role in eliminating excess cholesterol from peripheral cells by generating nascent high-density lipoprotein (HDL). However, it remains unclear whether both phospholipids and cholesterol are directly loaded onto apolipoprotein A-I (apoA-I) by ABCA1. To identify the amino acid residues of ABCA1 involved in substrate recognition and transport, we applied arginine scan mutagenesis to residues L821-E843 of human ABCA1 and predicted the environment to which each residue is exposed.

Fomiroid A, a novel compound from the mushroom Fomitopsis nigra, inhibits NPC1L1-mediated cholesterol uptake via a mode of action distinct from that of ezetimibe.

Hypercholesterolemia is one of the key risk factors for coronary heart disease, a major cause of death in developed countries. Suppression of NPC1L1-mediated dietary and biliary cholesterol absorption is predicted to be one of the most effective ways to reduce the risk of hypercholesterolemia. In a screen for natural products that inhibit ezetimibe glucuronide binding to NPC1L1, we found a novel compound, fomiroid A, in extracts of the mushroom Fomitopsis nigra.

ABCA1, ABCG1, and ABCG4 are distributed to distinct membrane meso-domains and disturb detergent-resistant domains on the plasma membrane.

ATP-binding cassette A1 (ABCA1), ABCG1, and ABCG4 are lipid transporters that mediate the efflux of cholesterol from cells. To analyze the characteristics of these lipid transporters, we examined and compared their distributions and lipid efflux activity on the plasma membrane. The efflux of cholesterol mediated by ABCA1 and ABCG1, but not ABCG4, was affected by a reduction of cellular sphingomyelin levels.

24(S)-hydroxycholesterol is actively eliminated from neuronal cells by ABCA1.

High cholesterol turnover catalyzed by cholesterol 24-hydroxylase is essential for neural functions, especially learning. Because 24(S)-hydroxycholesterol (24-OHC), produced by 24-hydroxylase, induces apoptosis of neuronal cells, it is vital to eliminate it rapidly from cells. Here, using differentiated SH-SY5Y neuron-like cells as a model, we examined whether 24-OHC is actively eliminated via transporters induced by its accumulation.

ATPase activity of nucleotide binding domains of human MDR3 in the context of MDR1.

Although human MDR1 and MDR3 share 86% similarity in their amino acid sequences and are predicted to share conserved domains for drug recognition, their physiological transport substrates are quite different: MDR1 transports xenobiotics and confers multidrug resistance, while MDR3 exports phosphatidylcholine into bile. Although MDR1 shows high ATPase activity, attempts to demonstrate the ATPase activity of human MDR3 have not succeeded. Therefore, it is possible that the difference in the functions of these proteins is caused by their different ATPase activities.

ATPase activity of human ABCG1 is stimulated by cholesterol and sphingomyelin.

ATP-binding cassette protein G1 (ABCG1) is important for the formation of HDL. However, the biochemical properties of ABCG1 have not been reported, and the mechanism of how ABCG1 is involved in HDL formation remains unclear. We established a procedure to express and purify human ABCG1 using the suspension-adapted human cell FreeStyle293-F.

Role of Dlg5/lp-dlg, a membrane-associated guanylate kinase family protein, in epithelial-mesenchymal transition in LLc-PK1 renal epithelial cells.

Discs large homolog 5 (Dlg5) is a member of the membrane-associated guanylate kinase adaptor family of proteins, some of which are involved in the regulation of epithelial-to-mesenchymal transition (EMT). Dlg5 has been described as a susceptibility gene for Crohn's disease; however, the physiological function of Dlg5 is unknown. We show here that transforming growth factor-β (TGF-β)-induced EMT suppresses Dlg5 expression in LLc-PK1 cells.

ATP hydrolysis-dependent conformational changes in the extracellular domain of ABCA1 are associated with apoA-I binding.

ATP-binding cassette protein A1 (ABCA1) plays a major role in cholesterol homeostasis and high-density lipoprotein (HDL) metabolism. Although it is predicted that apolipoprotein A-I (apoA-I) directly binds to ABCA1, the physiological importance of this interaction is still controversial and the conformation required for apoA-I binding is unclear. In this study, the role of the two nucleotide-binding domains (NBD) of ABCA1 in apoA-I binding was determined by inserting a TEV protease recognition sequence in the linker region of ABCA1.

Involvement of low-density lipoprotein receptor-related protein and ABCG1 in stimulation of axonal extension by apoE-containing lipoproteins.

Apolipoprotein E (apoE)-containing lipoproteins (LpE) are produced by glial cells in the central nervous system (CNS). When LpE are supplied to distal axons, but not cell bodies, of CNS neurons (retinal ganglion cells) the rate of axonal extension is increased. In this study we have investigated the molecular requirements underlying the stimulatory effect of LpE on axonal extension.

ATP-binding cassette proteins involved in glucose and lipid homeostasis.

Glucose and lipids are essential to the body, but excess glucose or lipids lead to metabolic syndrome. ATP-binding cassette (ABC) proteins are involved in the homeostasis of glucose and lipid in that they regulate insulin secretion and remove excess cholesterol from the body. Sulfonylurea receptor (SUR) is a subunit of the ATP-sensitive potassium channels, which regulate insulin secretion from pancreatic beta-cells by sensing cellular metabolic levels.

Molecular mechanisms of subcellular localization of ABCG5 and ABCG8.

Human ABCG subfamily proteins ABCG1, ABCG2, ABCG4, ABCG5, and ABCG8 are half-type ATP-binding cassette (ABC) proteins that transport sterols or xenobiotics. ABCG1, ABCG2, and ABCG4 function as homodimers on the plasma membrane. In contrast, ABCG5 and ABCG8 function as heterodimers on the plasma membrane, and the homodimer of either ABCG5 or ABCG8 is retained in the endoplasmic reticulum (ER).

Improved expression and purification of human multidrug resistance protein MDR1 from baculovirus-infected insect cells.

Multidrug resistance protein MDR1 (P-glycoprotein/ABCB1) is an ATP-dependent efflux pump for various cytotoxic agents, and is implicated in the resistance of human tumors to chemotherapeutic drugs. To achieve the three-dimensional structural analysis for its mechanistic implications, large amounts of high-quality and homogeneous MDR1 protein are essential. Here we report a cost-effective method for large-scale expression of human MDR1 using a baculovirus/insect expressSF+ cell system and an alterative purification method to maintain MDR1 in a monodispersed state.

Direct interaction of nuclear liver X receptor-beta with ABCA1 modulates cholesterol efflux.

Cholesterol is an essential component of eukaryotic cells; at the same time, however, hyperaccumulation of cholesterol is harmful. Therefore, the ABCA1 gene, the product of which mediates secretion of cholesterol, is highly regulated at both the transcriptional and post-transcriptional levels. The transcription of ABCA1 is regulated by intracellular oxysterol concentration via the nuclear liver X receptor (LXR)/retinoid X receptor (RXR); once synthesized, ABCA1 protein turns over rapidly with a half-life of 1-2 h.

Cholesterol fill-in model: mechanism for substrate recognition by ABC proteins.

Many of the 48 or 49 human ABC proteins are involved in lipid homeostasis and in defence against hydrophobic substances in food and the environment. Defects in their functions cause various diseases, suggesting that they play very important roles in human health; however, the mechanism of how they handle enormous numbers of hydrophobic compounds with various structures and molecular weights, or phospholipids and cholesterol, major components of cellular membranes, is not known. We compared the functions of drug-transporting and lipid-transporting ABC proteins, and found that (1) ABC proteins, either lipid or drug transporters, have a similar substrate binding site which recognizes PL and cholesterol, or drugs and cholesterol; (2) Cholesterol in membranes binds to various ABC proteins together with PL or drugs, and plays an important role in substrate recognition, especially by ABCB1/MDR1, where cholesterol fills the empty space in the substrate binding site when small drugs bind to it.