Sidhu A, Olde B, Humblot N, Kimura K, Gardner N
Department of Pediatrics, Georgetown University Medical Center, Georgetown University, Washington, DC 20007, USA.
Neuroscience. 1999;91(2):537-47. doi: 10.1016/s0306-4522(98)00555-7.
SK-N-MC human neuroblastoma cells express functional D1, but not D5, dopaminergic receptors. Stimulating cells with dopamine or the D1-selective agonist, SKF R-38393, rapidly (t(1/2) = 1 h) resulted in > 95% attenuation of dopamine-mediated accumulation of cyclic AMP, without any change in D1 dopamine receptor levels. Prolonged (> 4 h) exposure of cells to dopamine attenuated D1 receptor levels to 45-50% of control (t(1/2) = 8 h) and was accompanied by a loss of high-affinity binding sites. At the molecular level, the expression of D1 receptor messenger RNA was bimodal: an initial increase (by approximately 60%) of receptor messenger RNA within 2 h of treatment of cells with dopamine was followed by a decline to 50% below control messenger RNA levels. Low concentrations (1-10 nM) of dopamine also potentiated D1 messenger RNA levels (up to 48%), resulting in a twofold increase in receptor levels. Transfection studies with the cloned human D1 promoter construct, pGL-D1P, indicated that the up-regulation of D1 messenger RNA was due to activation of promoter by dopamine. The dopamine-mediated up-regulation of both D1 receptor messenger RNA and promoter was prevented by the D1-selective antagonist, SCH 23390. The results suggest that dopamine regulates D1 receptor gene and protein expression in a bimodal manner, partly through activation of the receptor promoter. Moreover, the effects of dopamine are independent of the second messenger, cyclic AMP.
SK-N-MC人神经母细胞瘤细胞表达功能性D1多巴胺能受体，但不表达D5受体。用多巴胺或D1选择性激动剂SKF R-38393刺激细胞，可迅速（半衰期t(1/2)=1小时）使多巴胺介导的环磷酸腺苷积累减少>95%，而D1多巴胺受体水平无任何变化。细胞长时间（>4小时）暴露于多巴胺会使D1受体水平降至对照的45 - 50%（半衰期t(1/2)=8小时），并伴有高亲和力结合位点的丧失。在分子水平上，D1受体信使核糖核酸（mRNA）的表达呈双峰模式：在用多巴胺处理细胞的2小时内，受体mRNA最初增加（约60%），随后降至对照mRNA水平以下50%。低浓度（1 - 10 nM）的多巴胺也会增强D1 mRNA水平（高达48%），导致受体水平增加两倍。用克隆的人D1启动子构建体pGL-D1P进行的转染研究表明，D1 mRNA的上调是由于多巴胺激活了启动子。D1选择性拮抗剂SCH 23390可阻止多巴胺介导的D1受体mRNA和启动子上调。结果表明，多巴胺以双峰方式调节D1受体基因和蛋白质表达，部分是通过激活受体启动子。此外，多巴胺的作用独立于第二信使环磷酸腺苷。
