Kudoh S, Komuro I, Mizuno T, Yamazaki T, Zou Y, Shiojima I, Takekoshi N, Yazaki Y
Department of Medicine III, University of Tokyo, School of Medicine, Japan.
Circ Res. 1997 Jan;80(1):139-46. doi: 10.1161/01.res.80.1.139.
Many lines of evidence have suggested that angiotensin II (Ang II)plays an important role in cardiac hypertrophy. Ang II not only increases protein synthesis but also induces the reprogramming of gene expression in cultured cardiac myocytes. In the present study, to elucidate the mechanism by which Ang II regulates gene expression in cardiac myocytes, we examined whether Ang II activates c-Jun NH2-terminal kinase (JNK), which is a member of the mitogen-activated protein kinase family and activates the transcription factor, activator protein-1 (AP-1). The activity of JNK increased 5 minutes after the addition of Ang II, peaked at 20 minutes, and gradually decreased thereafter. Examination of the Ang II dose-response relation revealed detectable JNK activation at 10(-9) mol/L and maximal activation at 10(-6) mol/L. Ang II activated JNK through the AT1 receptor, and the activation was attenuated by the downregulation of protein kinase C or the chelation of intracellular Ca2+. Although the addition of either Ca2+ ionophore or phorbol ester resulted in little or no activation of JNK, simultaneous addition of both Ca2+ ionophore and phorbol ester markedly activated JNK. Slight expressions of the c-jun gene were observed in unstimulated cardiac myocytes, and Ang II increased expressions of the c-jun gene as well as the c-fos gene. Ang II increased transcription of the endothelin-1 gene through the AP-1 binding site. In conclusion, Ang II may activate JNK in cultured cardiac myocytes through an increase in intracellular Ca2+ and activation of protein kinase C, and the activated JNK may regulate gene expression by activating AP-1 during Ang II-induced cardiac hypertrophy.
多条证据表明，血管紧张素II（Ang II）在心肌肥大中起重要作用。Ang II不仅增加蛋白质合成，还可诱导培养的心肌细胞中基因表达的重编程。在本研究中，为阐明Ang II调节心肌细胞基因表达的机制，我们检测了Ang II是否激活c-Jun氨基末端激酶（JNK），JNK是丝裂原活化蛋白激酶家族的成员之一，可激活转录因子活化蛋白-1（AP-1）。添加Ang II后5分钟，JNK活性增加，20分钟时达到峰值，此后逐渐下降。对Ang II剂量反应关系的检测显示，在10^(-9) mol/L时可检测到JNK激活，在10^(-6) mol/L时激活作用最大。Ang II通过AT1受体激活JNK，蛋白激酶C的下调或细胞内Ca2+的螯合可减弱这种激活作用。虽然单独添加Ca2+离子载体或佛波酯对JNK的激活作用很小或没有，但同时添加Ca2+离子载体和佛波酯可显著激活JNK。在未受刺激的心肌细胞中观察到c-jun基因有轻微表达，Ang II可增加c-jun基因以及c-fos基因的表达。Ang II通过AP-1结合位点增加内皮素-1基因的转录。总之，Ang II可能通过增加细胞内Ca2+和激活蛋白激酶C来激活培养的心肌细胞中的JNK，并且在Ang II诱导的心肌肥大过程中，激活的JNK可能通过激活AP-1来调节基因表达。
