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Selective Prostacyclin Receptor Agonism Augments Glucocorticoid-Induced Gene Expression in Human Bronchial Epithelial Cells¹

Sylvia M. Wilson,^* Pamela Shen,^2* Christopher F. Rider, Suzanne L. Traves,^* David Proud,^* Robert Newton, and Mark A. Giembycz^3*

^*Department of Physiology and Pharmacology and Department of Cell Biology and Anatomy, Airways Inflammation Research Group, Institute of Infection, Immunity and Inflammation, Faculty of Medicine, University of Calgary, Calgary, Alberta, Canada

Prostacyclin receptor (IP-receptor) agonists display anti-inflammatory and antiviral activity in cell-based assays and in preclinical models of asthma and chronic obstructive pulmonary disease. In this study, we have extended these observations by demonstrating that IP-receptor activation also can enhance the ability of glucocorticoids to induce genes with anti-inflammatory activity. BEAS-2B bronchial epithelial cells stably transfected with a glucocorticoid response element (GRE) luciferase reporter were activated in a concentration-dependent manner by the glucocorticoid dexamethasone. An IP-receptor agonist, taprostene, increased cAMP in these cells and augmented luciferase expression at all concentrations of dexamethasone examined. Analysis of the concentration-response relationship that described this effect showed that taprostene increased the magnitude of transcription without affecting the potency of dexamethasone and was, thus, steroid-sparing in this simple system. RO3244794, an IP-receptor antagonist, and oligonucleotides that selectively silenced the IP-receptor gene, PTGIR, abolished these effects of taprostene. Infection of BEAS-2B GRE reporter cells with an adenovirus vector encoding a highly selective inhibitor of cAMP-dependent protein kinase (PKA) also prevented taprostene from enhancing GRE-dependent transcription. In BEAS-2B cells and primary cultures of human airway epithelial cells, taprostene and dexamethasone interacted either additively or cooperatively in the expression of three glucocorticoid-inducible genes (GILZ, MKP-1, and p57^kip2) that have anti-inflammatory potential. Collectively, these data show that IP-receptor agonists can augment the ability of glucocorticoids to induce anti-inflammatory genes in human airway epithelial cells by activating a cAMP/PKA-dependent mechanism. This observation may have clinical relevance in the treatment of airway inflammatory diseases that are either refractory or respond suboptimally to glucocorticoids.

The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked advertisement in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

¹ This study was funded in part by the Canadian Institutes of Health Research (CIHR) and the GlaxoSmithKline/Collaborative Innovation Research Fund. R.N. is a CIHR New Investigator and an Alberta Heritage Foundation for Medical Research (AHFMR) Scholar. M.A.G. is an AHFMR Senior Scholar. D.P. holds a Canadian Research Chair in Inflammatory Lung Diseases.

² Current Address: Department of Pathology and Molecular Medicine, Centre for Gene Therapeutics, McMaster University, Hamilton, Ontario, Canada.

³ Address correspondence and reprint requests to Dr. Mark A. Giembycz, Department of Physiology and Pharmacology, Airways Inflammation Research Group, Institute of Infection, Immunity, and Inflammation, 3280 Hospital Drive Northwest, Calgary, Alberta, Canada T2N 4N1. E-mail address: giembycz{at}ucalgary.ca

⁴ Abbreviations used in this paper: PGI₂, prostacyclin; COPD, chronic obstructive pulmonary disease; GILZ, glucocorticoid-inducible leucine zipper; GR, glucocorticoid receptor; GRE, glucocorticoid response element; E/[A], agonist concentration effect; HEK, human embryonic kidney; HpAEC, human primary airway epithelial cell; ICS, inhaled glucocorticoid; IP-receptor, PGI₂ receptor; MKP, MAPK phosphatase; MOI, multiplicity of infection; p57^kip2, kinase inhibitor protein 2 of 57 kDa; PDE, phosphodiesterase; PKA, cAMP-dependent protein kinase A; PKI, PKA inhibitor; PPAR, peroxisome proliferator-activated receptor; SFM, serum-free medium; siRNA, small interfering RNA; TX, thromboxane.