ABC transporters form the largest of all transporter families, and their structural study has made tremendous progress over recent years. However, despite such advances, the precise mechanisms that determine the energy-coupling between ATP hydrolysis and the conformational changes following substrate binding remain to be elucidated. Here, we present our thermodynamic analysis for both ABC importers and exporters, and introduce the two new concepts of differential-binding energy and elastic conformational energy into the discussion. We hope that the structural analysis of ABC transporters will henceforth take thermodynamic aspects of transport mechanisms into account as well.
ATP-Binding Cassette Transporters ; physiology ; Adenosine Triphosphate ; metabolism ; Animals ; Humans ; Models, Theoretical ; Thermodynamics

OBJECTIVETo study the effects of high-density lipoprotein (HDL) and oxidized high-density lipoprotein (ox-HDL) on the expression of ATP-binding cassette transporter A1 (ABCAl) and cholesterol efflux in human umbilical vein endothelial cells (HUVECs).

METHODSIn vitro cultured HUVECs were incubated in the presence of 100 microg/ml HDL or 100 microg/ml ox-HDL for 24 h, using PBS as the negative control. ABCA1 mRNA level and cholesterol efflux rate were determined using RT-PCR and a liquid scintillator, respectively.

RESULTSHDL and ox-HDL significantly elevated the level of ABCA1 mRNA by 58% and 23% relative to the control level, respectively (P<0.05). The cholesterol efflux rate in ox-HDL group was significantly lower than that in HDL group (P<0.01).

CONCLUSIONHDL increases ABCAl expression and cholesterol efflux in HUVECs. Oxidative modification of HDL decrease cholesterol efflux by inhibiting the expression of ABCAl, suggesting a possible mechanism of ox-HDL in the pathogenesis of atherosclerosis.

ATP Binding Cassette Transporter 1 ; ATP-Binding Cassette Transporters ; genetics ; metabolism ; Cells, Cultured ; Cholesterol ; metabolism ; Endothelial Cells ; metabolism ; Humans ; Lipoproteins, HDL ; metabolism ; physiology ; Umbilical Veins ; cytology

ATP Binding Cassette Subfamily B Member 11 ; ATP Binding Cassette Transporter, Sub-Family G, Member 2 ; ATP-Binding Cassette Transporters ; physiology ; ATP-Binding Cassette, Sub-Family B, Member 1 ; physiology ; Animals ; Bile ; metabolism ; Biliary Tract ; physiology ; Drug Interactions ; Drug Resistance, Multiple ; Humans ; Liver ; physiology ; Multidrug Resistance-Associated Proteins ; physiology ; Neoplasm Proteins ; physiology ; Organic Anion Transporters ; physiology ; Organic Anion Transporters, Sodium-Dependent ; physiology ; Organic Cation Transport Proteins ; physiology ; Symporters ; physiology

OBJECTIVETo investigate the role of ATP-binding cassette transporter G1 (ABCG1) in endothelial dysfunction induced by high glucose.

METHODSHuman aortic endothelial cells (HAECs) were incubated in the presence of 5.6 or 30 mmol/L glucose for 24-72 h with or without a 2-h pretreatment with the LXR agonist 22(R)-hydroxycholesterol. Real-time PCR and Western blotting were used to measure the mRNA and protein expressions of ABCG1; the intracellular cholesterol efflux and endothelial nitric oxide synthase (eNOS) activity were measured by scintillation counting.

RESULTSHigh glucose time-dependently suppressed ABCG1 expression and cholesterol efflux to HDL in HAECs. High glucose also decreased eNOS activity. ABCG1 down-regulation induced by high glucose, along with decreased cholesterol efflux and eNOS activity, was abolished by treatment of the cells with the LXR agonist.

CONCLUSIONEndothelial dysfunction induced by high glucose is associated with decreased ABCG1 expression.

ATP Binding Cassette Transporter, Sub-Family G, Member 1 ; ATP-Binding Cassette Transporters ; genetics ; metabolism ; Aorta ; cytology ; Cell Line ; Down-Regulation ; drug effects ; Endothelial Cells ; cytology ; metabolism ; physiology ; Glucose ; pharmacology ; Humans

OBJECTIVE: To determine the effect and possible mechanism of an apolipoprotein (apo) A-I mimetic peptide, D-4F, on cholesterol efflux in RAW264.7 macrophages. METHODS: RAW264.7 macrophages were incubated in the medium containing 8-bromo cAMP (8-Br-cAMP, 0.5 mmol/L) and ox-LDL (50 μg/mL) for 24 h. Then various concentrations of D-4F (0-100 μg/mL) or H89 (20 μmol/L, a protein kinase A inhibitor) were added for the purpose of interference. The intracellular cyclic AMP (cAMP) level was determined by enzyme-linked immunoabsobant assay (ELISA). ATP binding cassette transporter A1 (ABCA1) expression in the macrophages was quantitated by real-time PCR and Western blot. RESULTS: D-4F significantly increased the cholesterol efflux in both concentration and time-dependent manner accompanied by the increase in the intracellular cAMP level, ABCA1 mRNA and protein expression. The effect of D-4F on cholesterol efflux ABCA1 expression was enhanced by 8-Br-cAMP. Although H89 did not affect the basal cholesterol efflux and ABCA1 expression, it could attenuate the effect of 8-Br cAMP. CONCLUSION D-4F affects cholesterol efflux, cAMP level, and ABCA1 expression in macrophages, which is likely involved in the pathway of cAMP/PKA/ABCA1.
ATP Binding Cassette Transporter 1 ; ATP-Binding Cassette Transporters ; metabolism ; Apolipoprotein A-I ; chemistry ; pharmacology ; Biological Transport ; drug effects ; physiology ; Biomimetics ; Cell Line ; Cholesterol ; metabolism ; Cyclic AMP ; metabolism ; Humans ; Macrophages ; cytology ; metabolism ; Peptides ; chemistry ; pharmacology

The present study was designed to analyze the metabolites of all-trans-retinal (atRal) and compare the cytotoxicity of atRal versus its derivative all-trans-retinoic acid (atRA) in human retinal pigment epithelial (RPE) cells. We confirmed that atRA was produced in normal pig neural retina and RPE. The amount of all-trans-retinol (atROL) converted from atRal was about 2.7 times that of atRal-derived atRA after incubating RPE cells with 10 μmol/L atRal for 24 h, whereas atRA in medium supernatant is more plentiful (91 vs. 29 pmol/mL), suggesting that atRA conversion facilitates elimination of excess atRal in the retina. Moreover, we found that mRNA expression of retinoic acid-specific hydroxylase CYP26b1 was dose-dependently up-regulated by atRal exposure in RPE cells, indicating that atRA inactivation may be also initiated in atRal-accumulated RPE cells. Our data show that atRA-caused viability inhibition was evidently reduced compared with the equal concentration of its precursor atRal. Excess accumulation of atRal provoked intracellular reactive oxygen species (ROS) overproduction, heme oxygenase-1 (HO-1) expression, and increased cleaved poly(ADP-ribose) polymerase 1 (PARP1) expression in RPE cells. In contrast, comparable dosage of atRA-induced oxidative stress was much weaker, and it could not activate apoptosis in RPE cells. These results suggest that atRA generation is an antidotal metabolism pathway for atRal in the retina. Moreover, we found that in the eyes of ABCA4^-/-RDH8^-/- mice, a mouse model with atRal accumulation in the retina, the atRA content was almost the same as that in the wild type. It is possible that atRal accumulation simultaneously and equally promotes atRA synthesis and clearance in eyes of ABCA4^-/-RDH8^-/- mice, thus inhibiting the further increase of atRA in the retina. Our present study provides further insights into atRal clearance in the retina.
ATP-Binding Cassette Transporters/physiology* ; Alcohol Oxidoreductases/physiology* ; Animals ; Cell Survival/drug effects* ; Cells, Cultured ; Humans ; Inactivation, Metabolic ; Mice ; Retina/metabolism* ; Retinal Pigment Epithelium/metabolism* ; Swine ; Tretinoin/pharmacology*

ATP-binding cassette (ABC) transporters are a family of proteins that mediate multi-drug resistance (MDR) via ATP-dependent drug efflux pumps. Abnormally expression and function would result in tumor MDR. That is the most important mechanism of MDR. The inhibition of ABC transporters as a strategy to reverse MDR in cancer has been studied extensively. In this review, we reviewed the structure and function of ABC transporters, and focused on the research advances in the mechanism of tumors MDR mediated by ABC transporters and the development of their modulators and reversal strategies.
ATP-Binding Cassette Transporters ; antagonists & inhibitors ; chemistry ; metabolism ; physiology ; Antineoplastic Agents ; therapeutic use ; Drug Resistance, Multiple ; Drug Resistance, Neoplasm ; Humans ; Neoplasms ; drug therapy ; physiopathology

Mitofusin2 (Mfn2) plays a pivotal role in the proliferation and apoptosis of vascular smooth muscle cells (VSMCs). The purpose of this study was to investigate the effects of Mfn2 on the trafficking of intracellular cholesterol in the foam cells derived from rat VSMCs (rVSMCs) and also to investigate the effects of Mfn2 on the expression of adenosine triphosphate-binding cassette subfamily A member 1 (ABCA1), adenosine triphosphate-binding cassette subfamily G member 1 (ABCG1) and peroxisome proliferator-activated receptor gamma (PPARγ). The rVSMCs were co-cultured with oxidized low density lipoprotein (LDL, 80 μg/mL) to produce foam cells and cholesterol accumulation in cells. Before oxidized LDL treatment, different titers (20, 40 and 60 pfu/cell) of recombinant adenovirus containing Mfn2 gene (Adv-Mfn2) were added into the culture medium for 24 h to transfect the Mfn2 gene into the rVSMCs. Then the cells were harvested for analyses. The protein expression of Mfn2 was significantly higher in Adv-Mfn2-transfected group than in untransfected group (P<0.05), and the expression levels significantly increased when the titer of Adv-Mfn2 increased (P<0.05). At 24 or 48 h after oxidized LDL treatment, rVSMCs became irregular and their nuclei became larger, and their plasma abounded with red lipid droplets. However, the number of red lipid droplets was significantly decreased in Adv-Mfn2-transfected group as compared with untransfected group. At 48 h after oxidized LDL treatment, the intracellular cholesterol in rVSMCs was significantly increased (P<0.05), but it was significantly decreased in Adv-Mfn2-transfected group as compared with untransfected group (P<0.05), and it also significantly decreased when the titer of Adv-Mfn2 increased (P<0.05). The mRNA and protein expression levels of ABCA1 and ABCG1 were significantly increased in Adv-Mfn2-transfected group as compared with untransfected group (P<0.05). Though the mRNA and protein expression levels of PPARγ was not significantly increased (P>0.05), the phosporylation levels of PPARγ were significantly decreased in Adv-Mfn2-transfected group as compared with untransfected group (P<0.05). These results suggest that the transfection of Adv-Mfn2 can significantly reduce intracellular cholesterol in oxidized LDL-induced rVSMCs possibly by decreasing PPARγ phosporylation and then increasing protein expression levels of ABCA1 and ABCG1, which may be helpful to suppress the formation of foam cells.
ATP Binding Cassette Transporter 1 ; metabolism ; ATP Binding Cassette Transporter, Sub-Family G, Member 1 ; ATP-Binding Cassette Transporters ; metabolism ; Animals ; Cell Differentiation ; physiology ; Cells, Cultured ; Cholesterol ; metabolism ; Foam Cells ; cytology ; metabolism ; Intracellular Fluid ; metabolism ; Lipoproteins, LDL ; metabolism ; Membrane Proteins ; genetics ; metabolism ; Mitochondrial Proteins ; genetics ; metabolism ; Muscle, Smooth, Vascular ; cytology ; metabolism ; Oxidation-Reduction ; PPAR gamma ; metabolism ; Rats

OBJECTIVE To explore downstream regulatory pathway of microRNA-21 (miR-21) in colon cancer cells (RKO) through detecting miR-21 and its target PDCD4, and the influence of miR-21 regulation on the sensitivity of RKO cells to 5-fluorouracil (5-FU). METHODS 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide (MTT) assay was used to determine the effect of 5-FU on the viability of RKO cells with knockout of miR-21 or high expression of PDCD4. Real-time was used to determine the expression of PDCD4, ABCC5 and CD44 in RKO cell after knockout of miR-21. RESULTS MTT assay reveals that the IC50 of 5-FU in RKO-WT cells (52.82 ± 0.06 umol/L) was about 67% higher than in miR-21 knockout cells (32.23 ± 0.05 umol/L) (P < 0.05), and the apoptosis ratio elevated after knockout of miR-21. High expression of PDCD4, a target gene of miR-21, can negatively regulate the expression of ABC transporter ABCC5 and the stem cell marker CD44. CONCLUSION MiR-21 can mediate the drug resistance to 5-FU by inhibiting its target PDCD4, which can regulate the expression of ABCC5 and CD44 genes.
ATP Binding Cassette Transporter, Sub-Family G, Member 5 ; ATP-Binding Cassette Transporters ; genetics ; Antimetabolites, Antineoplastic ; pharmacology ; Apoptosis Regulatory Proteins ; physiology ; Cell Line, Tumor ; Colonic Neoplasms ; drug therapy ; pathology ; Drug Resistance, Neoplasm ; Fluorouracil ; pharmacology ; Humans ; Hyaluronan Receptors ; genetics ; Lipoproteins ; genetics ; MicroRNAs ; physiology ; RNA-Binding Proteins ; physiology

BACKGROUNDABCA7 is a member of the ABCA subfamily that shows a high degree of homology to ABCA1 and, like ABCA1, mediates cellular cholesterol and phospholipid release by apolipoproteins when transfected in vitro. However, expression of ABCA7 has been shown to be downregulated by increased cellular cholesterol while ABCA1 was upregulated.

METHODSThe underlying mechanism for this effect was examined in ABCA1 or ABCA7-transfected HEC293. Lipid content in the medium and cells was determined by enzymatic assays. Gene expression was quantitated by real time PCR, and protein content was determined by Western blotting.

RESULTSWhile ABCA7 mRNA was decreased by 25-hydroxycholesterol treatment, ABCA1 was apparently increased. Treatment with the synthetic LXR agonist T0901317 (T09) upregulated ABCA1 expression and apoAI-mediated cellular lipid release in ABCA1-transfected HEC293 cells, but ABCA7 expression and cellular lipid release in ABCA7-transfected HEC293 cells showed no obvious changes.

CONCLUSIONThe ABCA7 gene is regulated by sterol in a direction opposite to that of ABCA1.

ATP Binding Cassette Transporter 1 ; analysis ; genetics ; physiology ; ATP-Binding Cassette Transporters ; analysis ; genetics ; physiology ; Amino Acid Sequence ; Apolipoprotein A-I ; physiology ; Gene Expression Regulation ; HEK293 Cells ; Humans ; Hydrocarbons, Fluorinated ; pharmacology ; Hydroxycholesterols ; pharmacology ; Lipid Metabolism ; Liver X Receptors ; Molecular Sequence Data ; Orphan Nuclear Receptors ; agonists ; Sulfonamides ; pharmacology