Potential role of Atp8a1 as plasma membrane aminophospholipid translocase in proliferating neuronal cells
Item
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Title
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Potential role of Atp8a1 as plasma membrane aminophospholipid translocase in proliferating neuronal cells
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Identifier
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d_2009_2013:848ef7efeedc:10192
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identifier
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10345
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Creator
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Levano, Kelly,
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Contributor
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Probal Banerjee
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Date
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2009
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Language
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English
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Publisher
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City University of New York.
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Subject
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Cellular biology | Neurosciences | Biochemistry | phosphatidylserine | Plasma Membrane Aminophospholipid translocase
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Abstract
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The inner leaflet-localized phospholipid PS undergoes a translocation to the outer leaflet of the plasma membrane in apoptotic cells to trigger recognition and phagocytic removal of these dying cells by PS receptor-bearing scavenger cells, such as microglia and macrophages. The enzyme activity responsible for the inner-membrane localization of PS is the plasma membrane aminophospholipid translocase (PLAPLT), also known as flippase, which translocates PS from the outer to the inner leaflet of the plasma membrane. Attempts to identify the PLAPLT molecule of mammalian cells have revealed a candidate molecule, Atp8a1, which is a P-type Mg-ATPase. After much controversy, it is currently believed that Atp8a1 translocates PS across internal membranes but not the plasma membrane. Based on our earlier studies showing overexpression of Atp8a1 in proliferating hybrid neuroblastoma cells causes an increase PLAPLT activity, we postulated that Atp8a1 functions as PLAPLT only in fast dividing cells, such as neurotumor cells or neuroblasts. This study used the fluorescent PS analogue, NBD-PS, to show that ectopic expression of Atp8a1 in the N18 neurotumor Vmax for this enzyme, which suggests that overexpression of Atp8a1 causes an increase in the PLAPLT molecules. This indicates that Atp8a1 is possibly identical to the PLAPLT molecule of the N18 cells. As a confirmation of this hypothesis we expressed phosphorylation-site mutants of Atp8a1 in the N18 cells to elicit a decrease in the Vmax value of PLAPLT, without significantly altering the Km value. The inhibition of the PLAPLT activity in N18 cells was also evidenced by a striking increase in surface staining of these cells with the PS-binding protein annexin V. According to our postulate Atp8a1 deletion should also cause PS exposure in neuroblasts harbored within the dentate gyrus (DG), which is a proliferative niche within the memory center termed hippocampus. In corroboration, we observed pronounced annexin V staining in both dissociated DG cells as well as cultured hippocampal slices of Atp8a1 (-/-) mice but not wild type mice. Such PS externalization should trigger phagocytosis of DG cells, which in turn could lead to a loss of hippocampal function. In support of this postulate we have observed that the Atp8a1 (-/-) mice suffer from possibly hippocampal-related learning defects. Therefore, Atp8a1 may play a crucial role in the maintenance of the functional integrity of the hippocampus. Additionally, our study reveals a potential strategy for the selective removal of the brain tumor cells through targeted suppression of Atp8a1 activity in brain cancer cells, which would lead to PS externalization and elimination of the cells by phagocytosis.
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Type
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dissertation
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Source
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2009_2013.csv
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degree
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Ph.D.
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Program
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Biochemistry
