The B₁-agonist [des-Arg¹⁰]-kallidin activates transcription factor NF-κB and induces homologous upregulation of the bradykinin B₁-receptor in cultured human lung fibroblasts

The bradykinin B₁-receptor is strongly upregulated under chronic inflammatory conditions. However, the mechanism and reason are not known. Because a better understanding of the mechanism of the upregulation will help in understanding its potential importance in inflammation, we have studied the molecular mechanism of B₁-receptor upregulation in cultured human lung fibroblasts (IMR 90) in response to IL-1β and the B₁-agonist [des-Arg¹⁰]- kallidin. We show that treatment of human IMR 90 cells by IL-1β stimulates the expression of both B₁-receptor mRNA and protein. The latter was studied by Western blot analysis using antipeptide antibodies directed against the COOH-terminal part of the human B₁-receptor. We furthermore report the novel observation that the B₁-receptor is upregulated by its own agonist which was completely blocked by the specific B₁-antagonist [des-Arg¹⁰-Leu⁹]- kallidin, indicating an upregulation entirely mediated through cell surface B₁-receptors. The increased population of B₁-receptors was functionally coupled as exemplified by an enhancement of the B₁-agonist induced increase in free cytosolic calcium. Upregulation by the B₁-agonist was blocked by a specific protein kinase C inhibitor. B₁-agonist-induced upregulation was correlated to the induction of transcription factor nuclear factor κB (NF- κB) which efficiently bound to the NF-κB-like sequence located in the promoter region of the human B₁-receptor gene. This correlation was further confirmed by reporter gene assays which showed that this NF-κB-like sequence, in the B₁-receptor promoter context, could contribute to IL-1β and DLBK-induced B₁-receptor transcription activation, and by the effect of NF-κB inhibitor pyrrolidinedithiocarbamate which diminished both B₁- receptor upregulation and NF-κB activation. NF-κB is now recognized as a key inflammatory mediator which is activated by the B₁-agonist but which is also involved in B₁-receptor upregulation.