title: ATP11C mutation is responsible for the defect in phosphatidylserine uptake in UPS-1 cells.
abstract: Type IV P-type ATPases (P4-ATPases) translocate phospholipids from the exoplasmic to the cytoplasmic leaflets of cellular membranes. We and others previously showed that ATP11C, a member of the P4-ATPases, translocates phosphatidylserine (PS) at the plasma membrane. Twenty years ago, the UPS-1 (uptake of fluorescent PS analogs) cell line was isolated from mutagenized Chinese hamster ovary (CHO)-K1 cells with a defect in nonendocytic uptake of nitrobenzoxadiazole PS. Due to its defect in PS uptake, the UPS-1 cell line has been used in an assay for PS-flipping activity; however, the gene(s) responsible for the defect have not been identified to date. Here, we found that the mRNA level of ATP11C was dramatically reduced in UPS-1 cells relative to parental CHO-K1 cells. By contrast, the level of ATP11A, another PS-flipping P4-ATPase at the plasma membrane, or CDC50A, which is essential for delivery of most P4-ATPases to the plasma membrane, was not affected in UPS-1 cells. Importantly, we identified a nonsense mutation in the ATP11C gene in UPS-1 cells, indicating that the intact ATP11C protein is not expressed. Moreover, exogenous expression of ATP11C can restore PS uptake in UPS-1 cells. These results indicate that lack of the functional ATP11C protein is responsible for the defect in PS uptake in UPS-1 cells and ATP11C is crucial for PS flipping in CHO-K1 cells.
authors.affiliation: Graduate School of Pharmaceutical Sciences, Kyoto University, Sakyo-ku; Kyoto 606-8501, Japan.
authors.forename: Naoto
authors.initials: N
authors.lastname: Takada
authors.affiliation: Graduate School of Pharmaceutical Sciences, Kyoto University, Sakyo-ku; Kyoto 606-8501, Japan.
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Takatsu
authors.affiliation: Graduate School of Pharmaceutical Sciences, Kyoto University, Sakyo-ku; Kyoto 606-8501, Japan.
authors.forename: Rie
authors.initials: R
authors.lastname: Miyano
authors.affiliation: Graduate School of Pharmaceutical Sciences, Kyoto University, Sakyo-ku; Kyoto 606-8501, Japan.
authors.forename: Kazuhisa
authors.initials: K
authors.lastname: Nakayama
authors.affiliation: Graduate School of Pharmaceutical Sciences, Kyoto University, Sakyo-ku; Kyoto 606-8501, Japan.
authors.forename: Hye-Won
authors.initials: HW
authors.lastname: Shin
mesh_terms: D000251:Adenosine Triphosphatases / Q000502:physiology*; D000818:Animals; D016466:CHO Cells; D002462:Cell Membrane / Q000201:enzymology; D006224:Cricetinae; D003412:Cricetulus; D006801:Humans; D026901:Membrane Transport Proteins / Q000502:physiology*; D010718:Phosphatidylserines / Q000378:metabolism*
chemical_list: D026901:Membrane Transport Proteins; D010718:Phosphatidylserines; C000588974:ATP11C protein, human; D000251:Adenosine Triphosphatases
keywords: adenosine triphosphatases; flippase; membrane bilayer; phospholipid; plasma membrane; uptake of fluorescent phosphatidylserine analogs