SELECTIVE REGULATION OF BETA-2-ADRENERGIC RECEPTOR GENE-EXPRESSION BY INTERLEUKIN-1 IN CULTURED HUMAN LUNG-TUMOR CELLS

The regulation of beta-1- and beta-2-adrenergic receptors (beta-1AR and beta-2AR) and receptor gene expression by interleukin-1-alpha (IL-1-alpha) was studied in cultured A549 human lung adenocarcinoma cells. The density and affinity of beta-1AR and beta-2AR were analyzed by computerized curve fitting of I-125-pindolol binding and its displacement by subtype selective antagonists. Steady state levels of receptor mRNAs were quantified by DNA excess solution hybridization assays. A549 cells in preconfluent cultures had fewer beta-1AR than beta-2AR (beta-1: 1.9 +/- 0.3 vs. beta-2: 4.0 +/- 0.5 fmol/mg protein, means +/- SE), but lost most of their beta-2AR upon reaching confluency (beta-1: 2.7 +/- 0.4, beta-2: 0.8 +/- 0.3 fmol/mg). Incubation of preconfluent cells for 24 hr with 20 pM of human recombinant IL-1-alpha did not modify the density of either of the beta-AR subtypes. Similar incubations of confluent cells increased the density of beta-2AR from 0.8 +/- 0.3 to 4.2 +/- 0.9 fmol/mg, while the density of beta-1AR and the antagonist affinities of both receptors remained unaltered. The IL-1-alpha-induced increase in beta-2AR density in confluent cells was antagonized in a concentration-dependent manner by a recombinant protein antagonist of type I IL-1 receptors (IC50: 0.2 nM). The IL-1-alpha-induced increase in beta-2AR density was preceded by an increase in the steady state level of beta-2AR mRNA, while levels of beta-1AR mRNA remained unchanged. IL-1-alpha increased the stability as well as the rate of transcription of beta-2AR mRNA. These findings demonstrate for the first time that activation of type I IL-1 receptors in A549 cells leads to a cell density-dependent, selective upregulation of beta-2AR, and that the mechanism of this effect involves increased formation and stability of the beta-2AR message.