Activation of beta(2)-adrenoceptor prevents shiga toxin 2-induced TNF-alpha gene transcription.

Exposure of renal tubular epithelial cells to shiga toxin 2 (Stx-2) causes cytotoxicity, and the potency of this toxin is enhanced in the presence of tumor necrosis factor-alpha (TNF-alpha). It has been shown that Stx-2 induces TNF-alpha production and that activation of beta(2)-adrenoceptors downregulates TNF-alpha. However, little is known about the signaling pathway by which beta(2)-adrenoceptor agonists suppress the Stx-2-induced TNF-alpha gene transcription. The possible signaling components involved in this pathway were investigated. Human adenocarcinoma-derived renal tubular epithelial cells (ACHN) were exposed to Stx-2 in the presence or absence of a beta(2)-adrenoceptor agonist. Mitogen-activated protein kinase (MAPK), activating protein-1 (AP-1), and nuclear factor-kappa B (NF-kappa B) were measured to evaluate the regulatory mechanisms involved in TNF-alpha gene transcription. Stx-2 (4 pg/ml) stimulated MAPK (p42/p44, p38) and AP-1 and increased TNF-alpha promoter activity by 2.4-fold. The increase in TNF-alpha was attenuated by both a p42/p44 inhibitor, PD098059 (10(-6) M), and a p38 inhibitor, SB203580 (10(-6) M), and AP-1-binding activity was inhibited by PD098059. Terbutaline (10(-6) M to 10(-8) M) suppressed MAPK (p42/p44, p38), NF-kappa B (p50, p65), and TNF-alpha promoter activity in a dose-dependent way that was prevented by the beta(2)-adrenoceptor antagonist, ICI118,551. However, inhibition of MAPK (p42/p44) and TNF-alpha promoter activity was partially prevented by the cAMP-protein kinase (PKA) inhibitors, H-89 (5 x 10(-6) M) and KT5720 (10(-5) M), whereas the suppression of p38 MAPK or NF-kappa B (p50) was not blocked by these inhibitors. The suppression of NF-kappa B (p65) was completely overcome by H-89 or KT5720. In summary, the downregulation of TNF-alpha transcription by terbutaline was mediated by an inhibitory effect of beta(2)-adrenoceptor activation on MAPK (p42/p44, p38) and NF-kappa B (p50/p65), which were exerted through a cAMP-PKA pathway and a cAMP-independent mechanism. It is likely that cAMP-PKA and MAPK (p42/p44, p38) may play a critical role in the regulation of the Stx-2-induced TNF-alpha transcription via beta(2)-adrenoceptor activation.