The regulation of beta1 and beta2-adrenergic receptors (beta1AR and beta2AR) and receptor gene expression by interleukin-1alpha (IL-1a) was studied in cultured A549 human lung adenocarcinoma cells. The density and affinity of beta1AR and beta2AR were analyzed by computerized curve fitting of 125-I-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 beta1AR than beta2AR (beta1: 1.9plus/minus0.3 vs beta2: 4.0plus/minus0.5 fmol/mg protein, mean plus/minus SE), but lost most of their beta2AR upon reaching confluency (beta1: 2.7plus/minus0.4, beta2: 0.8plus/minus 0.3 fmol/mg). Incubation of preconfluent cells for 24 hr with 20 pM of human recombinant IL-1a did not modify the density of either of the betaAR subtypes. Similar incubations of confluent cells increased the density of beta2AR from 0.8plus/minus0.3 to 4.2plus/minus0.9 fmol/mg, while the density of beta1AR and the antagonist affinities of both receptors remained unaltered. The IL-1a-induced increase in beta2AR 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-1a-induced increase in beta2AR density was preceded by an increase in the steady state level of beta2AR mRNA, while levels of beta1AR mRNA remained unchanged. The rate of transcription of the beta2AR mRNA was increased by IL-1a, as evidenced by the results of nuclear run-off assays.These observations indicate that activation of type I IL-1 receptors in A549 cells leads to a cell density-dependent, selective upregulation of beta2AR, and that the mechanism of this effect involves increased transcription of the beta2AR gene.
