Savard Martin, Barbaz David, Bélanger Simon, Müller-Esterl Werner, Bkaily Ghassan, D'orléans-Juste Pedro, Coté Jérôme, Bovenzi Veronica, Gobeil Fernand
Department of Pharmacology, Université de Sherbrooke, Sherbrooke, Québec, Canada.
J Cell Physiol. 2008 Jul;216(1):234-44. doi: 10.1002/jcp.21398.
Bradykinin (BK) represents a pro-inflammatory mediator that partakes in many inflammatory diseases. The mechanism of action of BK is thought to be primarily mediated by specific cell surface membrane B2 receptors (B2Rs). Some evidence has suggested, however, the existence of an intracellular/nuclear B2R population. Whether these receptors are functional and contribute to BK signaling remains to be determined. In this study, by mean of Western blotting, 3D-confocal microscopy, receptor autoradiography and radioligand binding analysis, we showed that plasma membrane and highly purified nuclei from isolated rat hepatocytes contain specific B2R that bind BK. The results depicting B2R nuclear expression in isolated nuclear organelles were reproduced in situ on hepatic sections by immunogold labeling and transmission electron microscopy. Functional tests on single nuclei, by means of confocal microscopy and the calcium-sensitive probe fluo-4AM, showed that BK induces concentration-dependent transitory mobilization of nucleoplasmic calcium; these responses were blocked by B2R antagonist HOE 140, not by the B1R antagonist R954 and, were also found in wild-type C57/Bl6 mice, but not in B2R-KO mice. In isolated nuclei, BK elicited activation/phosphorylation of Akt, acetylation of histone H3 and ensuing pro-inflammatory iNOS gene induction as determined by Western blot and RT-PCR. ChIP assay confirmed binding of acetylated-histone H3 complexes, but not B2R, to promoter region of iNOS gene suggesting that B2R-mediated gene expression is bridged with accessory downstream effectors. This study discloses a previously undescribed mechanism in BK-induced transcriptional events, via intracrine B2R-mediated signaling, occurring in rat autologous hepatic cells.
缓激肽(BK)是一种促炎介质,参与多种炎症性疾病。BK的作用机制被认为主要由特定的细胞表面膜B2受体(B2Rs)介导。然而,一些证据表明存在细胞内/核B2R群体。这些受体是否具有功能并参与BK信号传导仍有待确定。在本研究中,通过蛋白质印迹法、三维共聚焦显微镜、受体放射自显影和放射性配体结合分析,我们表明分离的大鼠肝细胞的质膜和高度纯化的细胞核含有与BK结合的特异性B2R。通过免疫金标记和透射电子显微镜在肝切片上原位重现了描绘分离的核细胞器中B2R核表达的结果。通过共聚焦显微镜和钙敏感探针fluo-4AM对单个细胞核进行功能测试,结果表明BK诱导核质钙的浓度依赖性瞬时动员;这些反应被B2R拮抗剂HOE 140阻断,而不是被B1R拮抗剂R954阻断,并且在野生型C57/Bl6小鼠中也发现了这些反应,但在B2R基因敲除小鼠中未发现。在分离的细胞核中,通过蛋白质印迹和逆转录-聚合酶链反应确定,BK引发了Akt的激活/磷酸化、组蛋白H3的乙酰化以及随后促炎诱导型一氧化氮合酶(iNOS)基因的诱导。染色质免疫沉淀分析证实乙酰化组蛋白H3复合物而非B2R与iNOS基因启动子区域结合,这表明B2R介导的基因表达与辅助下游效应器相关。本研究揭示了BK诱导的转录事件中一种先前未描述的机制,即通过大鼠自体肝细胞中发生的内分泌B2R介导的信号传导。