Edwards L, Fishman D, Horowitz P, Bourbon N, Kester M, Ernsberger P
Department of Nutrition, Case Western Reserve University School of Medicine, Cleveland, Ohio 44106-4906, USA.
J Neurochem. 2001 Dec;79(5):931-40. doi: 10.1046/j.1471-4159.2001.00632.x.
We sought to further elucidate signal transduction pathways for the I1-imidazoline receptor in PC12 cells by testing involvement of protein kinase C (PKC) isoforms (betaII, epsilon, zeta), and the mitogen-activated protein kinases (MAPK) ERK and JNK. Stimulation of I1-imidazoline receptor with moxonidine increased enzymatic activity of the classical betaII isoform in membranes by about 75% and redistributed the atypical isoform into membranes (40% increase in membrane-bound activity), but the novel isoform of PKC was unaffected. Moxonidine and clonidine also increased by greater than two-fold the proportion of ERK-1 and ERK-2 in the phosphorylated active form. In addition, JNK enzymatic activity was increased by exposure to moxonidine. Activation of ERK and JNK followed similar time courses with peaks at 90 min. The action of moxonidine on ERK activation was blocked by the I1-receptor antagonist efaroxan and by D609, an inhibitor of phosphatidylcholine-selective phospholipase C (PC-PLC), previously implicated as the initial event in I1-receptor signaling. Inhibition or depletion of PKC blocked activation of ERK by moxonidine. Two-day treatment of PC12 cells with the I1/alpha2-agonist clonidine increased cell number by up to 50% in a dose related manner. These data suggest that ERK and JNK, along with PKC, are signaling components of the I1-receptor pathway, and that this receptor may play a role in cell growth.
我们试图通过检测蛋白激酶C（PKC）亚型（βII、ε、ζ）以及丝裂原活化蛋白激酶（MAPK）ERK和JNK的参与情况，进一步阐明PC12细胞中I1-咪唑啉受体的信号转导途径。用莫索尼定刺激I1-咪唑啉受体可使膜中经典βII亚型的酶活性增加约75%，并使非典型亚型重新分布到膜中（膜结合活性增加40%），但PKC的新型亚型未受影响。莫索尼定和可乐定还使磷酸化活性形式的ERK-1和ERK-2的比例增加了两倍以上。此外，暴露于莫索尼定可增加JNK的酶活性。ERK和JNK的激活遵循相似的时间进程，在90分钟时达到峰值。莫索尼定对ERK激活的作用被I1受体拮抗剂依酚氯铵和D609（一种磷脂酰胆碱选择性磷脂酶C（PC-PLC）抑制剂，先前被认为是I1受体信号传导的初始事件）阻断。PKC的抑制或耗竭可阻断莫索尼定对ERK的激活。用I1/α2激动剂可乐定对PC12细胞进行为期两天的处理，可使细胞数量以剂量相关的方式增加多达50%。这些数据表明，ERK和JNK以及PKC是I1受体途径的信号传导成分，并且该受体可能在细胞生长中起作用。
