Abstract
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.
Highlights
The plasma membrane in eukaryotes envelops cells and consists of a bilayer structure of glycerophospholipids, sphingolipids and cholesterol [1] with embedded proteins
Using the C6-NBD-PS analog as well as fluorescently labeled PE and PC we examined in this study i) the ability of major leukocyte subsets to translocate specific phospholipids between the bilayer of the plasma membrane, and ii) whether the P4-type ATPase ATP11C is involved in this aminophospholipid translocation activity
We first wanted to test whether immune cell subsets translocate specific aminophospholipids between the two leaflets of the plasma membrane and compare the flippase activity between major subsets in different tissues
Summary
The plasma membrane in eukaryotes envelops cells and consists of a bilayer structure of glycerophospholipids, sphingolipids and cholesterol [1] with embedded proteins. One of the unique features of the plasma membrane is the asymmetric distribution of specific phospholipids between the two leaflets of the bilayer [2]. Phosphatidylcholine (PC) and sphingomyelin are predominantly present on the exoplasmic leaflet, while phosphatidylserine (PS) and PLOS ONE | DOI:10.1371/journal.pone.0146774. Phosphatidylcholine (PC) and sphingomyelin are predominantly present on the exoplasmic leaflet, while phosphatidylserine (PS) and PLOS ONE | DOI:10.1371/journal.pone.0146774 January 22, 2016
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