Singal Tushi, Dhalla Naranjan S, Tappia Paramjit S
Institute of Cardiovascular Sciences, St. Boniface Hospital Research Centre and Department of Physiology, University of Manitoba, Winnipeg, Canada.
J Mol Cell Cardiol. 2006 Jul;41(1):126-37. doi: 10.1016/j.yjmcc.2006.03.004. Epub 2006 May 22.
Previously, we have reported that norepinephrine (NE)-mediated cardiac hypertrophy may occur due to stimulation of alpha1-adrenoceptors and phospholipase C (PLC) activity. Since the signal transduction mechanisms involving PLC isozymes in cardiomyocytes are not well established, the present study was conducted to test the hypothesis that stimulation of cardiac PLC activity by NE increases the gene expression for PLC isozymes via a PKC and ERK 1/2-dependent pathway. For this purpose, mRNA levels for PLC beta1, beta3, gamma1, and delta1 isozymes were determined in isolated adult rat cardiomyocytes upon incubation in the absence and presence of NE. The NE-induced increases in PLC isozyme mRNA levels were not only attenuated by prazosin, an inhibitor of alpha1-adrenergic receptor, but also by U73122, an inhibitor of PLC activity. Alterations in NE-induced PLC gene expression by both prazosin and U73122 were associated with inhibition of PLC activity. The inhibition of NE-stimulated PLC gene expression by bisindolylmaleimide, a PKC inhibitor, and PD98059, an ERK1/2 inhibitor, indicated that PKC-MAPK signaling may be involved in this signal transduction pathway. The observed NE-induced changes in gene expression in the presence of different inhibitors were associated with corresponding changes in the protein content. Furthermore, significant increases in mRNA levels and protein contents for all PLC isozymes were found in cardiomyocytes treated with phorbol 12-myristate 13-acetate, a PKC activator. These data indicate that PLC isozymes may regulate their own gene expression through a PKC and ERK 1/2-dependent pathway in a cycle of events associated with the cardiomyocyte hypertrophic response.
此前，我们曾报道，去甲肾上腺素（NE）介导的心肌肥大可能是由于α1-肾上腺素能受体的刺激和磷脂酶C（PLC）活性增加所致。由于心肌细胞中涉及PLC同工酶的信号转导机制尚未完全明确，因此开展了本研究，以验证以下假说：NE刺激心脏PLC活性可通过蛋白激酶C（PKC）和细胞外信号调节激酶1/2（ERK 1/2）依赖性途径增加PLC同工酶的基因表达。为此，在分离的成年大鼠心肌细胞中，于不存在和存在NE的情况下孵育后，测定了PLC β1、β3、γ1和δ1同工酶的mRNA水平。NE诱导的PLC同工酶mRNA水平升高不仅被α1-肾上腺素能受体抑制剂哌唑嗪所减弱，也被PLC活性抑制剂U73122所减弱。哌唑嗪和U73122对NE诱导的PLC基因表达的改变均与PLC活性的抑制有关。PKC抑制剂双吲哚马来酰胺和ERK1/2抑制剂PD98059对NE刺激的PLC基因表达的抑制表明，PKC-丝裂原活化蛋白激酶（MAPK）信号通路可能参与了这一信号转导途径。在存在不同抑制剂的情况下观察到的NE诱导的基因表达变化与蛋白质含量的相应变化相关。此外，在用PKC激活剂佛波醇12-肉豆蔻酸酯13-乙酸酯处理的心肌细胞中，发现所有PLC同工酶的mRNA水平和蛋白质含量均显著增加。这些数据表明，PLC同工酶可能在与心肌细胞肥大反应相关的一系列事件中，通过PKC和ERK 1/2依赖性途径调节其自身的基因表达。
