Dual regulation of β2-adrenoceptor messenger RNA expression in human lung fibroblasts by β2-cAMP signaling; delayed upregulated inhibitors oppose a rapid in onset, direct stimulation of gene expression.
Based on their bronchodilatory effect, β2-adrenoceptor agonists constitute essential elements in the treatment of bronchial asthma and COPD. As treatment with β2-adrenoceptor agonists has been associated with worsening of airway hyper-reactivity, possibly because of loss of β-adrenoceptor function, molecular mechanism of the regulation of β2-adrenoceptor expression were studied. MRC-5 human lung fibroblasts were cultured in absence or presence of test substances followed by β2-adrenoceptor messenger RNA (mRNA) determination by qPCR. After inhibition of mRNA synthesis by actinomycin D, β2-adrenoceptor mRNA decreased with a half-life of 23 min, whereas inhibition of protein synthesis by cycloheximide caused an about 5- and 6-fold increase within 1.5 and 4 h, respectively. β2-Adrenoceptor mRNA was increased by about 100 % after 1 h exposure to formoterol or olodaterol but decreased by about 60 % after 4 h agonist exposure. Both effects of β2-adrenoceptor agonists were mimicked by forskolin, a direct activator of adenylyl cyclase and cholera toxin, which stimulates adenylyl cyclase by permanent activation of Gs. β2-Adrenoceptor agonist-induced upregulation of β2-adrenoceptor mRNA was blocked by the β2-adrenoceptor antagonist ICI 118551 and prevented by actinomycin D, but not by cycloheximide. Moreover, in presence of cycloheximide, β2-adrenoceptor agonist-induced reduction in β2-adrenoceptor mRNA was converted into stimulation, resulting in a more than 10-fold increase. In conclusion, expression of β2-adrenoceptors in human lung fibroblasts is highly regulated at transcriptional level. The β2-adrenoceptor gene is under strong inhibitory control of short-living suppressor proteins. β2-Adrenoceptor activation induces via adenylyl cyclase - cyclic adenosine monophosphate (cAMP) signaling a rapid in onset direct stimulation of the β2-adrenoceptor gene transcription, an effect opposed by a delayed upregulation of inhibitory factors.
Institute of Pharmacology & Toxicology, University of Bonn, Biomedical Center, Sigmund-Freud-Str. 25, D-53105, Bonn, Germany.
N
N
Kämpfer
F
F
Lamyel
I
I
Schütz
M
M
Warnken
K
K
Hoffmann
I
I
von Kügelgen
Kurt
K
Racké
D002460:Cell Line; D000242:Cyclic AMP / Q000378:metabolism*; D005347:Fibroblasts / Q000378:metabolism*; D006801:Humans; D008168:Lung / Q000166:cytology; D012333:RNA, Messenger / Q000378:metabolism*; D018343:Receptors, Adrenergic, beta-2 / Q000235:genetics* / Q000378:metabolism*; D015398:Signal Transduction; D015854:Up-Regulation
D012333:RNA, Messenger; D018343:Receptors, Adrenergic, beta-2; D000242:Cyclic AMP