Role of the PI3-kinase signaling pathway in trafficking of the surfactant protein A receptor P63 (CKAP4) on type II pneumocytes

Am J Physiol Lung Cell Mol Physiol. 2010 Dec;299(6):L794-807. doi: 10.1152/ajplung.00372.2009. Epub 2010 Sep 24.

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.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Alveolar Epithelial Cells / cytology
  • Alveolar Epithelial Cells / metabolism*
  • Animals
  • Cell Membrane / metabolism
  • Cells, Cultured
  • Cyclic AMP / metabolism
  • Enzyme Activation
  • Enzyme Inhibitors / metabolism
  • Humans
  • Liposomes / chemistry
  • Liposomes / metabolism
  • Membrane Proteins / genetics
  • Membrane Proteins / metabolism*
  • Phosphatidylinositol 3-Kinase / metabolism*
  • Proto-Oncogene Proteins c-akt / metabolism
  • Pulmonary Surfactant-Associated Protein A / metabolism*
  • Rats
  • Receptors, Cell Surface / genetics
  • Receptors, Cell Surface / metabolism*
  • Signal Transduction / physiology*

Substances

  • CKAP4 protein, human
  • CKAP4 protein, rat
  • Enzyme Inhibitors
  • Liposomes
  • Membrane Proteins
  • Pulmonary Surfactant-Associated Protein A
  • Receptors, Cell Surface
  • surfactant protein A receptor
  • Cyclic AMP
  • Phosphatidylinositol 3-Kinase
  • Proto-Oncogene Proteins c-akt