title: Role of the PI3-kinase signaling pathway in trafficking of the surfactant protein A receptor P63 (CKAP4) on type II pneumocytes.
abstract: Surfactant protein A (SP-A) plays an important role in the maintenance of lung lipid homeostasis. Previously, an SP-A receptor, P63 (CKAP4), on type II pneumocyte plasma membranes (PM) was identified by chemical cross-linking techniques. An antibody to P63 blocked the specific binding of SP-A to pneumocytes and the ability of SP-A to regulate surfactant secretion. The current report shows that another biological activity of SP-A, the stimulation of surfactant uptake by pneumocytes, is inhibited by P63 antibody. cAMP exposure resulted in enrichment of P63 on the cell surface as shown by stimulation of SP-A binding, enhanced association of labeled P63 antibody with type II cells, and promotion of SP-A-mediated liposome uptake, all of which were inhibited by competing P63 antibody. Incubation of A549 and type II cells with SP-A also increased P63 localization on the PM. The phosphatidylinositol 3-kinase (PI3-kinase) signaling pathway was explored as a mechanism for the transport of this endoplasmic reticulum (ER)-resident protein to the PM. Treatment with LY-294002, an inhibitor of the PI3-kinase pathway, prevented the SP-A-induced PM enrichment of P63. Exposure of pneumocytes to SP-A or cAMP activated Akt (PKB). Blocking either PI3-kinase or Akt altered SP-A-mediated lipid turnover. The data demonstrate an important role for the PI3-kinase-Akt pathway in intracellular transport of P63. The results add to the growing body of evidence that P63 is critical for SP-A receptor-mediated interactions with type II pneumocytes and the resultant regulation of surfactant turnover.
authors.affiliation: Institute for Environmental Medicine, Univ. of Pennsylvania School of Medicine, Philadelphia, 19104-6068, USA.
authors.forename: Altaf S
authors.initials: AS
authors.lastname: Kazi
authors.forename: Jian-Qin
authors.initials: JQ
authors.lastname: Tao
authors.forename: Sheldon I
authors.initials: SI
authors.lastname: Feinstein
authors.forename: Li
authors.initials: L
authors.lastname: Zhang
authors.forename: Aron B
authors.initials: AB
authors.lastname: Fisher
authors.forename: Sandra R
authors.initials: SR
authors.lastname: Bates
mesh_terms: D056809:Alveolar Epithelial Cells / Q000166:cytology / Q000378:metabolism*; D000818:Animals; D002462:Cell Membrane / Q000378:metabolism; D002478:Cells, Cultured; D000242:Cyclic AMP / Q000378:metabolism; D004789:Enzyme Activation; D004791:Enzyme Inhibitors / Q000378:metabolism; D006801:Humans; D008081:Liposomes / Q000737:chemistry / Q000378:metabolism; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D058539:Phosphatidylinositol 3-Kinase / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D037662:Pulmonary Surfactant-Associated Protein A / Q000378:metabolism*; D051381:Rats; D011956:Receptors, Cell Surface / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction / Q000502:physiology*
chemical_list: C081876:CKAP4 protein, human; C554951:CKAP4 protein, rat; D004791:Enzyme Inhibitors; D008081:Liposomes; D008565:Membrane Proteins; D037662:Pulmonary Surfactant-Associated Protein A; D011956:Receptors, Cell Surface; C067774:surfactant protein A receptor; D000242:Cyclic AMP; D058539:Phosphatidylinositol 3-Kinase; D051057:Proto-Oncogene Proteins c-akt