Post-transcriptional regulation of bradykinin B1 and B2 receptor gene expression in human lung fibroblasts by tumor...

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 alpha (TNF-alpha) and interleukin 1beta (IL-1beta). TNF-alpha and IL-1beta 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 [(3)H]des-Arg(10)-kallidin, and [(3)H]bradykinin, respectively. The induced B1 receptors were functionally coupled, because the B1 agonist, des-Arg(10)-kallidin, induced an increase in arachidonic acid release in TNF-alpha-stimulated cells but not in control cells. The induction of B1 and the up-regulation of B2 receptors by TNF-alpha was partly mediated through activation of p38 mitogen-activated protein kinase and that of B2 receptor by protein kinase A. TNF-alpha and IL-1beta 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.