title: Pim-1L Protects Cell Surface-Resident ABCA1 From Lysosomal Degradation in Hepatocytes and Thereby Regulates Plasma High-Density Lipoprotein Level.
abstract: ATP-binding cassette transporter A1 (ABCA1) exerts an atheroprotective action through the biogenesis of high-density lipoprotein in hepatocytes and prevents the formation of foam cells from macrophages. Controlling ABCA1 is a rational approach to improving atherosclerotic cardiovascular disease. Although much is known about the regulatory mechanism of ABCA1 synthesis, the molecular mechanism underpinning its degradation remains to be clearly described.
  
  
  
  ABCA1 possesses potential sites of phosphorylation by serine/threonine-protein kinase Pim-1 (Pim-1). Pim-1 depletion decreased the expression of cell surface-resident ABCA1 (csABCA1) and apolipoprotein A-I-mediated [3H]cholesterol efflux in the human hepatoma cell line HepG2, but not in peritoneal macrophages from mice. In vitro kinase assay, immunoprecipitation, and immunocytochemistry suggested phosphorylation of csABCA1 by the long form of Pim-1 (Pim-1L). Cell surface biotinylation indicated that Pim-1L inhibited lysosomal degradation of csABCA1 involving the liver X receptor β, which interacts with csABCA1 and thereby protects it from ubiquitination and subsequent lysosomal degradation. Cell surface coimmunoprecipitation with COS-1 cells expressing extracellularly hemagglutinin-tagged ABCA1 showed that Pim-1L-mediated phosphorylation of csABCA1 facilitated the interaction between csABCA1 and liver X receptor β and thereby stabilized the csABCA1-Pim-1L complex. Mice deficient in Pim-1 kinase activity showed lower expression of ABCA1 in liver plasma membranes and lower plasma high-density lipoprotein levels than control mice.
  
  
  
  Pim-1L protects hepatic csABCA1 from lysosomal degradation by facilitating the physical interaction between csABCA1 and liver X receptor β and subsequent stabilization of the csABCA1-Pim-1L complex and thereby regulates the circulating level of high-density lipoprotein. Our findings may aid the development of high-density lipoprotein-targeted therapy.
authors.affiliation: From the Laboratory of Molecular Pharmacokinetics, Graduate School of Pharmaceutical Sciences, The University of Tokyo, Japan.
authors.forename: Akira
authors.initials: A
authors.lastname: Katsube
authors.affiliation: From the Laboratory of Molecular Pharmacokinetics, Graduate School of Pharmaceutical Sciences, The University of Tokyo, Japan. hayapi@mol.f.u-tokyo.ac.jp.
authors.forename: Hisamitsu
authors.initials: H
authors.lastname: Hayashi
authors.affiliation: From the Laboratory of Molecular Pharmacokinetics, Graduate School of Pharmaceutical Sciences, The University of Tokyo, Japan.
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Kusuhara
mesh_terms: D064286:ATP Binding Cassette Transporter 1 / Q000235:genetics / Q000378:metabolism*; D000818:Animals; D016632:Apolipoprotein A-I / Q000378:metabolism; D019556:COS Cells; D002462:Cell Membrane / Q000378:metabolism*; D002522:Chlorocebus aethiops; D057809:HEK293 Cells; D056945:Hep G2 Cells; D022781:Hepatocytes / Q000201:enzymology*; D006801:Humans; D008075:Lipoproteins, HDL / Q000097:blood*; D000071518:Liver X Receptors / Q000378:metabolism; D008247:Lysosomes / Q000201:enzymology*; D017737:Macrophages, Peritoneal / Q000378:metabolism; D008297:Male; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D010766:Phosphorylation; D011485:Protein Binding; D055550:Protein Stability; D059748:Proteolysis; D051573:Proto-Oncogene Proteins c-pim-1 / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D034622:RNA Interference; D014162:Transfection
chemical_list: D064286:ATP Binding Cassette Transporter 1; D016632:Apolipoprotein A-I; D008075:Lipoproteins, HDL; D000071518:Liver X Receptors; D051573:Proto-Oncogene Proteins c-pim-1; C577836:ABCA1 protein, human; C577833:Abca1 protein, mouse; C505693:APOA1 protein, human; C496634:PIM1 protein, human; C496636:Pim1 protein, mouse
keywords: ATP-binding cassette transporters; Pim-1 kinase; atherosclerosis; hepatocytes; high-density lipoprotein; liver X receptor β