Inhibition of human airway smooth muscle cell proliferation by β2-adrenergic receptors and cAMP is PKA independent: Evidence for EPAC involvement

Karen M. Kassel, Todd A. Wyatt, Reynold A. Panettieri, Myron L. Toews

Research output: Contribution to journalArticle

67 Scopus citations

Abstract

Mechanisms by which β-adrenergic receptor (βAR) agonists inhibit proliferation of human airway smooth muscle (HASM) cells were investigated because of their potential relevance to smooth muscle hyperplasia in asthma. We hypothesized that βAR agonists would inhibit mitogenesis in HASM cells via the β2AR, an increase in cAMP, and PKA activation. HASM cells were treated for 24 h with various agents and then analyzed for [ 3H]thymidine incorporation as a measure of cell proliferation. EGF stimulated proliferation by ∼10-fold. The nonselective βAR agonist isoproterenol and the β2AR-selective agonists albuterol and salmeterol inhibited EGF-stimulated proliferation by more than 50%, with half-maximal effects at 4.8 nM, 110 nM, and 6.7 nM, respectively. A β2AR-selective antagonist inhibited the isoproterenol effect with 100-fold greater potency than a β1AR-selective antagonist, confirming β2AR involvement in the inhibition of proliferation. The cAMP-elevating agents PGE2 and forskolin decreased EGF-induced proliferation, suggesting cAMP as the mediator. β2AR agonists and forskolin also inhibited proliferation stimulated by lysophosphatidic acid (LPA) as well as the synergistic proliferation stimulated by LPA+EGF. Importantly, PKA-selective cAMP analogs did not inhibit proliferation at concentrations that maximally activated PKA (10-100 μM), whereas a cAMP analog selective for the exchange protein directly activated by cAMP (EPAC), 8-(4-chlorophenylthio)-2′-O-methyl-cAMP, maximally inhibited proliferation at a concentration that did not activate PKA (10 μM). These data show that β2AR agonists and other cAMP-elevating agents decrease proliferation in HASM cells via a PKA-independent mechanism, and they provide pharmacological evidence for involvement of EPAC or an EPAC-like cAMP effector protein instead.

Original languageEnglish (US)
Pages (from-to)L131-L138
JournalAmerican Journal of Physiology - Lung Cellular and Molecular Physiology
Volume294
Issue number1
DOIs
StatePublished - Jan 2008

Keywords

  • Asthma
  • Epidermal growth factor
  • Exchange protein directly activated by cAMP
  • Lysophosphatidic acid

ASJC Scopus subject areas

  • Physiology
  • Pulmonary and Respiratory Medicine
  • Physiology (medical)
  • Cell Biology

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