Importin 13 regulates nuclear import of the glucocorticoid receptor in airway epithelial cells

Am J Respir Cell Mol Biol. 2006 Dec;35(6):668-80. doi: 10.1165/rcmb.2006-0073OC. Epub 2006 Jun 29.


Antiinflammatory effects of glucocorticoids are critical to treatment of airway inflammation in such common disorders as asthma. There is considerable variation in responsiveness to glucocorticoid, and prolonged exposure can result in glucocorticoid resistance. We cloned LGL2, a glucocorticoid-inducible gene in fetal rat lung. We described the characterization of lgl2 as a nuclear transport protein, classified as importin 13 (IPO13), and demonstrated developmental regulation of IPO13 nucleocytoplasmic shuttling. We now report on the identification of the glucocorticoid receptor (GR) as a cargo substrate for IPO13. Binding of GR and IPO13 was demonstrated by GR-GST pulldown and coimmunoprecipitation. To investigate the role of IPO13 in modulating GR signaling in the lung, we studied IPO13-regulated GR transport in airway epithelial cells. Small interfering RNAs that inhibited IPO13 synthesis prevented nuclear translocation of GR. Silencing of IPO13 also abrogated the ability of cortisol to inhibit synthesis of the inflammatory cytokine IL-8 after stimulation with TNF-alpha. Our findings support a role for IPO13 in promoting nuclear occupancy of GR in a way that strongly potentiates the antiinflammatory effects of glucocorticoids. We speculate that variation in cellular levels of IPO13 and intracellular IPO13 shuttling rates may contribute to glucocorticoid resistance.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Active Transport, Cell Nucleus / drug effects
  • Animals
  • Anti-Inflammatory Agents / pharmacology
  • Cell Nucleus / drug effects
  • Cell Nucleus / metabolism*
  • Drug Resistance
  • HeLa Cells
  • Humans
  • Hydrocortisone / pharmacology
  • Immunoprecipitation
  • Interleukin-8 / biosynthesis
  • Protein Binding
  • RNA Interference
  • RNA, Small Interfering / genetics
  • RNA, Small Interfering / metabolism
  • Rats
  • Rats, Wistar
  • Receptors, Glucocorticoid / drug effects
  • Receptors, Glucocorticoid / genetics
  • Receptors, Glucocorticoid / metabolism*
  • Recombinant Fusion Proteins / metabolism
  • Respiratory Mucosa / cytology
  • Respiratory Mucosa / drug effects
  • Respiratory Mucosa / metabolism*
  • Transfection
  • Tumor Necrosis Factor-alpha / pharmacology
  • Up-Regulation / drug effects
  • beta Karyopherins / genetics
  • beta Karyopherins / metabolism*


  • Anti-Inflammatory Agents
  • Interleukin-8
  • Ipo13 protein, rat
  • RNA, Small Interfering
  • Receptors, Glucocorticoid
  • Recombinant Fusion Proteins
  • Tumor Necrosis Factor-alpha
  • beta Karyopherins
  • Hydrocortisone