Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:3.6.1.3 (ATPase)
 65,361 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Cytotoxicity by unconjugated bilirubin involves disturbances of membrane structure, excitotoxicity and cell death. These events were reported to trigger elevated free radicals production and impairment of calcium homeostasis, and to result in loss of cell membrane integrity. Therefore, this study was designed to investigate whether interaction of clinically relevant concentrations of free unconjugated bilirubin with synaptosomal membrane vesicles could be linked to oxidative stress, cytosolic calcium accumulation and perturbation of membrane function. Synaptosomal vesicles were prepared from gerbil cortical brain tissue and incubated with purified bilirubin (<or=1 microM), for 4 h at 37 degrees C. Intracellular concentrations of reactive oxygen species (ROS) and calcium were determined by dichlorofluorescin and BAPTA fluorescent probes, respectively. Membrane protein and lipid oxidation were evaluated by immunocytochemistry and phosphatidylserine exposure by annexin V binding. Levels of reduced and oxidized glutathione (GSH and GSSG, respectively), as well as activities of Mg(2+)-ATPase aminophospholipid translocase (flippase) and Na(+),K(+)-ATPase, were also measured. Our results showed that bilirubin induced oxidative stress, due to a rise in lipid (>or=10%, P<0.05) and protein oxidation (>or=20%, P<0.01), ROS content (approximately 17%, P<0.01), and a decrease in GSH/GSSG ratio (>30%, P<0.01). In addition, synaptosomes exposed to bilirubin exhibited increased externalization of phosphatidylserine (approximately 10%, P<0.05), together with decreased flippase and NA(+),K(+)-ATPase (>or=15%, P<0.05) activities, events that were accompanied by enhanced intracellular calcium levels ( approximately 20%, P<0.01). The data obtained point out that interaction of unconjugated bilirubin with synaptosomal membrane vesicles leads to oxidative injury, loss of membrane asymmetry and functionality, and calcium intrusion, thus potentially contributing to the pathogenesis of encephalopathy by hyperbilirubinemia.
 ...
PMID:A link between hyperbilirubinemia, oxidative stress and injury to neocortical synaptosomes. 1547 95

The maintenance of phospholipid asymmetry in membrane bilayers is a paradigm in cell biology. However, the mechanisms and proteins involved in phospholipid translocation are still poorly understood. Members of the type 4 subfamily of P-type ATPases have been implicated in the translocation of phospholipids from the outer to the inner leaflet of membrane bilayers. In humans, several inherited disorders have been identified which are associated with loci harboring type 4 P-type ATPase genes. Up to now, one inherited disorder, Byler disease or progressive familial intrahepatic cholestasis type 1 (PFIC1), has been directly linked to mutations in a type 4 P-type ATPase gene. How the absence of an aminophospholipid translocase activity relates to this severe disease is, however, still unclear. Studies in the yeast Saccharomyces cerevisiae have recently identified important roles for type 4 P-type ATPases in intracellular membrane- and protein-trafficking events. These processes require an (amino)phospholipid translocase activity to initiate budding or fusion of membrane vesicles from or with other membranes. The studies in yeast have greatly contributed to our cell biological insight in membrane dynamics and intracellular-trafficking events; if this knowledge can be translated to mammalian cells and organs, it will help to elucidate the molecular mechanisms which underlie severe inherited human diseases such as Byler disease.
 ...
PMID:The type 4 subfamily of P-type ATPases, putative aminophospholipid translocases with a role in human disease. 1591 84

The most common therapeutic strategy for the treatment of cancer uses antimetabolites, which block uncontrolled division of cancer cells and kill them. However, such antimetabolites also kill normal cells, thus yielding detrimental side effects. This emphasizes the need for an alternative therapy, which would have little or no side effects. Our approach involves designing genetic means to alter surface lipid determinants that induce phagocytosis of cancer cells. The specific target of this strategy has been the enzyme activity termed aminophospholipid translocase (APLT) or flippase that causes translocation of phosphatidylserine (PS) from the outer to the inner leaflet of the plasma membrane in viable cells. Efforts to identify the enigmatic, plasma membrane APLT of mammalian cells have led investigators to some P-type ATPases, which have often proven to be the APLT of internal membranes rather than the plasma membrane. By measuring kinetic parameters for the plasma membrane APLT activity, we have shown that the P-type ATPase Atp8a1 is the plasma membrane APLT of the tumorigenic N18 cells, but not the non-tumorigenic HN2 (hippocampal neuron x N18) cells. Targeted knockdown of this enzyme causes PS externalization in the N18 cells, which would trigger phagocytic removal of these cells. But how would we specifically express the mutants or antisense Atp8a1 in the cancer cells? This has brought us to a glycosyltransferase, GnT-V, which is highly expressed in the transformed cells. By using the GnT-V promoter to drive a luciferase reporter gene we have demonstrated a dramatic increase in luciferase expression selectively in tumor cells. The described strategy could be tested for the removal of cancer cells without the use of antimetabolites that often kill normal cells.
 ...
PMID:A genetic strategy involving a glycosyltransferase promoter and a lipid translocating enzyme to eliminate cancer cells. 1928 71

The molecule responsible for the enzyme activity plasma membrane (PM) aminophospholipid translocase (APLT), which catalyzes phosphatidylserine (PS) translocation from the outer to the inner leaflet of the plasma membrane, is unknown in mammals. A Caenorhabditis elegans study has shown that ablation of transbilayer amphipath transporter-1 (TAT-1), which is an ortholog of a mammalian P-type ATPase, Atp8a1, causes PS externalization in the germ cells. We demonstrate here that the hippocampal cells of the dentate gyrus, and Cornu Ammonis (CA1, CA3) in mice lacking Atp8a1 exhibit a dramatic increase in PS externalization. Although their hippocampi showed no abnormal morphology or heightened apoptosis, these mice displayed increased activity and a marked deficiency in hippocampus-dependent learning, but no hyper-anxiety. Such observations indicate that Atp8a1 plays a crucial role in PM-APLT activity in the neuronal cells. In corroboration, ectopic expression of Atp8a1 but not its close homolog, Atp8a2, caused an increase in the population (V(max) ) of PM-APLT without any change in its signature parameter K(m) in the neuronal N18 cells. Conversely, expression of a P-type phosphorylation-site mutant of Atp8a1 (Atp8a1*) caused a decrease in V(max) of PM-APLT without significantly altering its K(m) . The Atp8a1*-expressing N18 cells also exhibited PS externalization without apoptosis. Together, our data strongly indicate that Atp8a1 plays a central role in the PM-APLT activity of some mammalian cells, such as the neuronal N18 and hippocampal cells.
 ...
PMID:Atp8a1 deficiency is associated with phosphatidylserine externalization in hippocampus and delayed hippocampus-dependent learning. 2200 59

In order to define the molecular anatomy of the blood-brain barrier (BBB) that may be relevant to either barrier or transport function, proteins that are overexpressed in the cerebral microvessels should be identified. We used differential display to identify novel proteins that are overexpressed or unique to the BBB. DNA sequence analysis is one of the differentially expressed transcripts showed that it is highly homologous with the ATPase class I, type 8B, and member 1 (ATP8B1) protein and contains an ATPase domain and a phospholipid-binding domain. ATP8B1 is expressed in the BBB microvessels but not brain tissue lacking microvessels. Likewise, ATP8B1 was enriched in BBB microvessels similar to glucose transporter 1. Immunohistochemistry using an ATP8B1-specific antibody demonstrated preferential staining of the microvessels within the cerebral tissue. These results suggest that ATP8B1, a P-type aminophospholipid translocase, is enriched in cerebral microvessels and may have a role in plasma membrane lipid transport.
 ...
PMID:Identification of ATP8B1 as a blood-brain barrier-enriched protein. 2464 66

Organization of the plasma membrane into specialized substructures in different blood lineages facilitates important biological functions including proper localization of receptors at the plasma membrane as well as the initiation of crucial intracellular signaling cascades. The eukaryotic plasma membrane is a lipid bilayer that consists of asymmetrically distributed phospholipids. This asymmetry is actively maintained by membrane-embedded lipid transporters, but there is only limited data available about the molecular identity of the predominantly active transporters and their substrate specificity in different leukocyte subsets. We demonstrate here that the P4-type ATPase ATP11C mediates significant flippase activity in all murine leukocyte subsets. Loss of ATP11C resulted in a defective internalization of phosphatidylserine (PS) and phosphatidylethanolamine (PE) in comparison to control cells. The diminished flippase activity caused increased PS exposure on 7-aminoactinomycin D- (7-AAD-) viable pro-B cells freshly isolated from the bone marrow of ATP11C-deficient mice, which was corrected upon a 2-hour resting period in vitro. Despite the impaired flippase activity in all immune cell subsets, the only other blood cell type with an accumulation of PS on the surface were viable 7-AAD- developing T cells but this did not result in any discernable effect on their development in the thymus. These findings show that all leukocyte lineages exhibit flippase activity, and identify ATP11C as an aminophospholipid translocase in immune cells.
...
PMID:ATP11C Facilitates Phospholipid Translocation across the Plasma Membrane of All Leukocytes. 2679 98


<< Previous 1 2 3