Dual regulation of β(2)-adrenoceptor messenger RNA expression in human lung fibroblasts by β(2)–cAMP signaling; delayed upregulated inhibitors oppose a rapid in onset, direct stimulation of gene expression

Based on their bronchodilatory effect, β(2)-adrenoceptor agonists constitute essential elements in the treatment of bronchial asthma and COPD. As treatment with β(2)-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 β(2)-adrenoceptor expression were studied. MRC-5 human lung fibroblasts were cultured in absence or presence of test substances followed by β(2)-adrenoceptor messenger RNA (mRNA) determination by qPCR. After inhibition of mRNA synthesis by actinomycin D, β(2)-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. β(2)-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 β(2)-adrenoceptor agonists were mimicked by forskolin, a direct activator of adenylyl cyclase and cholera toxin, which stimulates adenylyl cyclase by permanent activation of Gs. β(2)-Adrenoceptor agonist-induced upregulation of β(2)-adrenoceptor mRNA was blocked by the β(2)-adrenoceptor antagonist ICI 118551 and prevented by actinomycin D, but not by cycloheximide. Moreover, in presence of cycloheximide, β(2)-adrenoceptor agonist-induced reduction in β(2)-adrenoceptor mRNA was converted into stimulation, resulting in a more than 10-fold increase. In conclusion, expression of β(2)-adrenoceptors in human lung fibroblasts is highly regulated at transcriptional level. The β(2)-adrenoceptor gene is under strong inhibitory control of short-living suppressor proteins. β(2)-Adrenoceptor activation induces via adenylyl cyclase - cyclic adenosine monophosphate (cAMP) signaling a rapid in onset direct stimulation of the β(2)-adrenoceptor gene transcription, an effect opposed by a delayed upregulation of inhibitory factors.