Kim K A, Chakraborti T, Goldstein G W, Bressler J P
Department of Neurology, Johns Hopkins University School of Public Health and Hygiene and The Kennedy Krieger Research Institute, Baltimore, Maryland 21205, USA.
J Neurochem. 2000 Mar;74(3):1140-6. doi: 10.1046/j.1471-4159.2000.741140.x.
We previously demonstrated induction of c-fos mRNA in PC12 cells exposed to lead that was dependent on new transcription. In the current work, we examined two signal transduction mechanisms that are activated by lead and have been shown to mediate induction of c-fos mRNA. One mechanism involves protein kinase C, and the other requires calmodulin-dependent protein kinase II. Significant increases in the levels of c-fos, c-jun, and egr-1 but not NGFIB mRNA were observed in PC12 cells exposed to lead or phorbol 12-myristate 13-acetate. In contrast, PC12 cells depolarized with 56 mM K+ displayed an increase in c-fos, egr-1, and NGFIB but not c-jun mRNA. Similar to other activators of protein kinase C, lead increased AP-1 and Egr-1 DNA binding activity. Additionally, lead increased luciferase activity in cerebellar granule cells transfected with an AP-1 luciferase reporter construct. Lead did not increase c-fos mRNA in PC12 cells that were depleted of protein kinase C by a 24-h treatment with phorbol 12,13-dibutyrate or incubated with the protein kinase C inhibitor H-7. In contrast, an inhibitor of calmodulin-dependent protein kinase, KN-62, and an inhibitor of calmodulin, W-7, did not block the induction of c-fos mRNA by lead. An increase in serum-response element DNA-binding activity was observed in nuclear extracts from PC12 cells exposed to lead. It is interesting that lead activated protein kinase C isoforms delta and epsilon, but not isoforms alpha and beta. In conclusion, lead appears to induce the expression of immediate early genes by a mechanism that requires protein kinase C.
我们之前证明，暴露于铅的PC12细胞中c-fos mRNA的诱导依赖于新的转录。在当前研究中，我们研究了两种由铅激活且已被证明介导c-fos mRNA诱导的信号转导机制。一种机制涉及蛋白激酶C，另一种需要钙调蛋白依赖性蛋白激酶II。在暴露于铅或佛波酯12-肉豆蔻酸酯13-乙酸酯的PC12细胞中，观察到c-fos、c-jun和egr-1的水平显著增加，但NGFIB mRNA水平未增加。相比之下，用56 mM K+去极化的PC12细胞中，c-fos、egr-1和NGFIB增加，但c-jun mRNA未增加。与蛋白激酶C的其他激活剂类似，铅增加了AP-1和Egr-1的DNA结合活性。此外，铅增加了用AP-1荧光素酶报告构建体转染的小脑颗粒细胞中的荧光素酶活性。用佛波酯12,13-二丁酸酯进行24小时处理使蛋白激酶C耗尽或与蛋白激酶C抑制剂H-7孵育的PC12细胞中，铅未增加c-fos mRNA。相反，钙调蛋白依赖性蛋白激酶抑制剂KN-62和钙调蛋白抑制剂W-7并未阻断铅对c-fos mRNA的诱导。在暴露于铅的PC12细胞核提取物中观察到血清反应元件DNA结合活性增加。有趣的是，铅激活了蛋白激酶C亚型δ和ε，但未激活亚型α和β。总之，铅似乎通过一种需要蛋白激酶C的机制诱导立即早期基因的表达。
