Nakamura Akio, Johns Edward J, Imaizumi Akira, Yanagawa Yukishige, Kohsaka Takao
Department of Paediatrics, Teikyo University School of Medicine, Tokyo, Japan.
Department of Physiology, University of Birmingham, Birmingham, United Kingdom.
J Am Soc Nephrol. 2001 Nov;12(11):2288-2299. doi: 10.1681/ASN.V12112288.
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.
肾小管上皮细胞暴露于志贺毒素2（Stx - 2）会导致细胞毒性，并且在肿瘤坏死因子 - α（TNF - α）存在的情况下这种毒素的毒性会增强。已表明Stx - 2诱导TNF - α的产生，并且β₂ - 肾上腺素能受体的激活会下调TNF - α。然而，关于β₂ - 肾上腺素能受体激动剂抑制Stx - 2诱导的TNF - α基因转录的信号通路知之甚少。研究了该通路中可能涉及的信号成分。在存在或不存在β₂ - 肾上腺素能受体激动剂的情况下，将人腺癌来源的肾小管上皮细胞（ACHN）暴露于Stx - 2。测量丝裂原活化蛋白激酶（MAPK）、活化蛋白 - 1（AP - 1）和核因子 - κB（NF - κB），以评估参与TNF - α基因转录的调控机制。Stx - 2（4 pg/ml）刺激MAPK（p42/p44、p38）和AP - 1，并使TNF - α启动子活性增加2.4倍。p42/p44抑制剂PD098059（10⁻⁶ M）和p38抑制剂SB203580（10⁻⁶ M）均减弱了TNF - α的增加，并且PD098059抑制了AP - 1结合活性。特布他林（10⁻⁶ M至10⁻⁸ M）以剂量依赖的方式抑制MAPK（p42/p44、p38）、NF - κB（p50、p65）和TNF - α启动子活性，β₂ - 肾上腺素能受体拮抗剂ICI118,551可阻止这种抑制作用。然而，cAMP - 蛋白激酶（PKA）抑制剂H - 89（5×10⁻⁶ M）和KT5720（10⁻⁵ M）部分阻止了MAPK（p42/p44）和TNF - α启动子活性的抑制，而这些抑制剂并未阻断p38 MAPK或NF - κB（p50）的抑制。H - 89或KT5720完全克服了NF - κB（p65）的抑制。总之，特布他林对TNF - α转录的下调是由β₂ - 肾上腺素能受体激活对MAPK（p42/p44、p38）和NF - κB（p50/p65）的抑制作用介导的，这是通过cAMP - PKA途径和一种不依赖cAMP的机制实现的。cAMP - PKA和MAPK（p42/p44、p38）可能在通过β₂ - 肾上腺素能受体激活调控Stx - 2诱导的TNF - α转录中起关键作用。
