Laboratory of Neuropsychopharmacology, Department of Psychiatry and Neurosciences, University of South Florida College of Medicine, Tampa, FL, USA.
Neuroscience. 2010 Nov 24;171(1):12-22. doi: 10.1016/j.neuroscience.2010.09.005. Epub 2010 Sep 17.
Sustained exposure to nicotine is well known to increase the cell surface density of α4β2* neuronal nicotinic receptors both in vivo and in vitro, but the cellular mechanisms mediating this effect are equivocal. Using a pharmacological approach to investigate the effects of nicotine on receptor subunit expression and phosphorylation in SH-EP1 cells expressing human α4 and β2 nicotinic receptor subunits, we have demonstrated that incubation with nicotine for 24 h increased the expression of immature and mature forms of both α4 and β2 subunits in a concentration-dependent manner, and that inhibition of protein kinase C (PKC), but not cAMP-dependent protein kinase (PKA) inhibited the nicotine-induced increased expression of subunits. Incubation of cells with nicotine for 24 h also increased the phosphorylation of immature forms of α4 subunits similar to that induced by activation of either PKC or PKA. When cells were preincubated with nicotine, the PKC-mediated increased phosphorylation was inhibited; the PKA-mediated phosphorylation was unaltered. The phosphopeptide maps for immature α4 subunits following nicotine exposure or PKC activation were identical, and phosphoamino acid analyses indicated phosphorylation on serine residues only. Results indicate that nicotine-induced up regulation of α4β2 neuronal nicotinic receptors involves a PKC-dependent mechanism and likely reflects the ability of nicotine to activate PKC, leading to the phosphorylation of immature α4 subunits, promoting subunit assembly and receptor maturation. Because up regulation of these receptors has been implicated to mediate tolerance, locomotor sensitization and addiction to nicotine, results identify a potential new target for modulating the effects of nicotine on the brain.
持续暴露于尼古丁会增加体内和体外 α4β2*神经元烟碱受体的细胞表面密度，但介导这种效应的细胞机制尚存在争议。本研究采用药理学方法研究尼古丁对表达人 α4 和 β2 烟碱受体亚单位的 SH-EP1 细胞中受体亚单位表达和磷酸化的影响，结果表明，尼古丁孵育 24 小时可浓度依赖性地增加 α4 和 β2 亚基的未成熟和成熟形式的表达，而蛋白激酶 C（PKC）抑制剂而非 cAMP 依赖性蛋白激酶（PKA）可抑制尼古丁诱导的亚基表达增加。尼古丁孵育 24 小时还增加了 α4 亚基未成熟形式的磷酸化，类似于 PKC 或 PKA 激活所诱导的磷酸化。当细胞用尼古丁预孵育时，PKC 介导的增加的磷酸化被抑制；PKA 介导的磷酸化未改变。暴露于尼古丁或 PKC 激活后，未成熟 α4 亚基的磷酸肽图谱相同，磷酸氨基酸分析表明仅磷酸化丝氨酸残基。结果表明，尼古丁诱导的 α4β2 神经元烟碱受体上调涉及 PKC 依赖性机制，可能反映了尼古丁激活 PKC 的能力，导致未成熟 α4 亚基的磷酸化，促进亚基组装和受体成熟。由于这些受体的上调与尼古丁引起的耐受、运动敏化和成瘾有关，结果确定了调节尼古丁对大脑影响的一个新的潜在靶点。
