Post-Transcriptional Regulation of Bradykinin B1 and B2 Receptor Gene Expression in Human Lung Fibroblasts by Tumor Necrosis Factor-a: Modulation by Dexamethasone

The cellular and molecular mechanisms governing bradykinin B1 and B2 receptor expression and function are poorly understood. We investigated the regulation of both B1 and B2 receptors in human embryonic lung fibroblasts (HEL 299) by the proinflammatory cytokines tumor necrosis factor a (TNF-a) and interleukin 1b (IL-1b). TNF-a and IL-1b both induced a rapid and transient increase in B1 and B2 receptor mRNA expression that was maximal by 2 h, accompanied by an increase in B1 and B2 receptor protein, as measured by radioligand binding assay with [H]des-Arg-kallidin, and [H]bradykinin, respectively. The induced B1 receptors were functionally coupled, because the B1 agonist, des-Arg-kallidin, induced an increase in arachidonic acid release in TNF-a-stimulated cells but not in control cells. The induction of B1 and the up-regulation of B2 receptors by TNF-a was partly mediated through activation of p38 mitogen-activated protein kinase and that of B2 receptor by protein kinase A. TNF-a and IL-1b regulation of both B1 and B2 receptors was inhibited by dexamethasone. When compared with vehicle-treated cells, dexamethasone increased the rate of decline of both B1 and B2 receptor mRNAs. Nuclear run-on experiments demonstrate that the induction of B1 and the up-regulation of B2 receptors as well as the inhibitory effect of dexamethasone are entirely mediated through post-transcriptional mechanisms. Bradykinin (BK) and the related peptide kallidin (KD or lys-BK) are formed from high and low molecular weight kininogen precursors following the activation of plasma and tissue kallikreins by pathophysiological stimuli such as tissue damage, inflammation, or anoxia (Farmer and Burch, 1992; Hall, 1992). There is considerable evidence to suggest that BK plays a key role in airway inflammation and inflammatory diseases such as asthma and rhinitis (Barnes, 1992; Trifilieff et al., 1993). The biological actions of kinins are mediated via an interaction with constitutive B2 receptors and inducible B1 receptors. These receptors have been defined initially based on pharmacological criteria, and subsequently by molecular cloning (Hess et al., 1992; Menke et al., 1994; Webb et al., 1994) and both receptors belong to the G-protein-coupled receptor family. B2 receptors show a higher affinity for BK and KD, whereas B1 receptors show a higher affinity toward the metabolites [des-Arg]BK and [des-Arg]KD. Most of the biological actions of BK appear to be mediated through the activation of B2 receptors. Studies in different cell types have shown that activation of the B2 receptor leads to a number of intracellular events, including activation of phospholipase C, an increase in intracellular calcium, and activation of phospholipase D and PLA2 with subsequent release of arachidonic acid (Farmer and Burch,