Regulation of astrocytic glutamate transporter expression by Akt: evidence for a selective transcriptional effect on the GLT-1/EAAT2 subtype
Regulation of astrocytic glutamate transporter expression by Akt: evidence for a selective transcriptional effect on the GLT-1/EAAT2 subtype
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DOI：
10.1111/j.1471-4159.2006.03743.x
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发表时间：
2006-05-01
影响因子：
4.7
通讯作者：
Robinson, MB
中科院分区：
文献类型：
--
作者：
Li, LB;Toan, SV;Robinson, MB
在神经系统中，星形胶质细胞表达不同比例的两种神经胶质谷氨酸转运蛋白，即谷氨酸转运蛋白亚型 1 (GLT-1) 和谷氨酸/天冬氨酸转运蛋白 (GLAST)，但对于独立调节其表达的信号通路知之甚少。在星形胶质细胞培养物中，二丁酰-cAMP、表皮生长因子 (EGF) 或其他生长因子的治疗均会诱导 GLT-1 的表达并增加 GLAST 的表达。 GLT-1 的诱导与形态和生化变化相关，这些变化与星形胶质细胞的成熟一致。药理学研究表明磷脂酰肌醇3激酶(PI-3K)和核转录因子-κB(NF-κB)可能参与GLT-1表达的诱导。在多种信号系统中，Akt（也称为蛋白激酶 B (PKB)）在 PI-3K 下游发挥作用。在目前的这些研究中，我们使用工程化表达 Akt 显性失活 (DN)、组成型活性 (CA) 或无效变体的慢病毒载体来研究 Akt 可能参与 GLT-1 的调节。 DN-Akt 的表达减弱了 GLT-1 的 EGF 依赖性诱导。 CA-Akt 的表达导致 GLT-1 蛋白呈剂量和时间依赖性增加，增加 GLT-1 mRNA 水平，增加二氢红藻氨酸敏感性（可能是 GLT-1 介导的）转运活性，并导致星形胶质细胞形态变化为更星状形状，但对 GLAST 蛋白水平没有影响。最后，CA-Akt 的表达增加了报告基因构建体的表达，该报告基因构建体含有来自 GLT-1 人类同源物的推定启动子片段（称为 EAAT2）。从这些研究中，我们得出结论，Akt 通过增加转录来诱导 GLT-1 的表达，并且 Akt 可以调节 GLT-1 的表达而不增加星形胶质细胞中 GLAST 的表达。
In the nervous system, astrocytes express different ratios of the two glial glutamate transporters, glutamate transporter subtype 1 (GLT-1) and glutamate/aspartate transporter (GLAST), but little is known about the signaling pathways that independently regulate their expression. Treatment with dibutyryl-cAMP, epidermal growth factor (EGF) or other growth factors both induces expression of GLT-1 and increases expression of GLAST in astrocyte cultures. The induction of GLT-1 is correlated with morphological and biochemical changes that are consistent with astrocyte maturation. Pharmacological studies suggest that phosphatidylinositol 3-kinase (PI-3K) and the nuclear transcription factor-kappa B (NF-kappa B) may be involved in the induction of GLT-1 expression. In several signaling systems Akt, also known as protein kinase B (PKB), functions downstream of PI-3K. In these present studies we used lentiviral vectors engineered to express dominant-negative (DN), constitutively active (CA), or null variants of Akt to study the possible involvement of Akt in the regulation of GLT-1. Expression of DN-Akt attenuated the EGF-dependent induction of GLT-1. Expression of CA-Akt caused a dose- and time-dependent increase in GLT-1 protein, increased GLT-1 mRNA levels, increased dihydrokainate-sensitive (presumably GLT-1 mediated) transport activity, and caused a change in astrocyte morphology to a more stellate shape, but had no effect on GLAST protein levels. Finally, the expression of CA-Akt increased the expression of a reporter construct containing a putative promoter fragment from the human homolog of GLT-1, called EAAT2. From these studies, we conclude that Akt induces the expression of GLT-1 through increased transcription and that Akt can regulate GLT-1 expression without increasing GLAST expression in astrocytes.