Lau K F, Miller C C, Anderton B H, Shaw P C
Department of Biochemistry, The Chinese University of Hong Kong, Shatin, N.T., Hong Kong, China.
Genomics. 1999 Sep 1;60(2):121-8. doi: 10.1006/geno.1999.5875.
Glycogen synthase kinase 3beta (GSK-3beta) is a proline-directed kinase that forms part of the wingless signaling pathway. Recent studies have shown that GSK-3beta phosphorylates the microtubule-associated protein tau in vitro and in cell culture. Tau is the principal component of the paired helical filaments (PHFs) found in the brains of patients with Alzheimer disease, and PHF-tau is hyperphosphorylated. GSK-3beta is therefore one of the candidate kinases for phosphorylating tau in Alzheimer disease. GSK-3beta activity is negatively regulated by phosphorylation on serine 9 and positively regulated by phosphorylation on tyrosine 216. However, since overexpression of GSK-3beta by transfection leads to increased activity in the absence of any stimuli, GSK-3beta activity may also be regulated at the transcriptional level. Indeed, increased GSK-3beta protein levels are found in Alzheimer disease brains, and GSK-3beta is found associated with PHFs in Alzheimer disease. To understand how GSK-3beta activity may be regulated at the transcriptional level, we have isolated the human GSK-3beta promoter. The GSK-3beta promoter does not contain a conventional TATA box although several other transcription factor binding sites were identified. A putative transcription start site was mapped by 5' RACE. Transfection of various GSK-3beta promoter CAT reporter genes into both COS-7 cells and SHSY5Y neuronal cells revealed that the GSK-3beta promoter is more active in neuronal cells. Such transfection studies involving promoter deletion mutants revealed that a negative transcriptional response element may be present at position -1421 to -1363 and an activator sequence at position -427 to -384. CP2 binding sites were also present within the promoter. CP2 has recently been shown to interact with the Alzheimer disease amyloid precursor protein binding protein Fe65. The significance of these results with respect to Alzheimer disease pathogenesis are discussed.
糖原合酶激酶3β（GSK - 3β）是一种脯氨酸定向激酶，是无翅信号通路的一部分。最近的研究表明，GSK - 3β在体外和细胞培养中可使微管相关蛋白tau磷酸化。Tau是阿尔茨海默病患者大脑中双螺旋丝（PHF）的主要成分，且PHF - tau存在过度磷酸化。因此，GSK - 3β是阿尔茨海默病中使tau磷酸化的候选激酶之一。GSK - 3β的活性受丝氨酸9位点磷酸化的负调控以及酪氨酸216位点磷酸化的正调控。然而，由于通过转染过度表达GSK - 3β会在无任何刺激的情况下导致活性增加，GSK - 3β的活性也可能在转录水平受到调控。实际上，在阿尔茨海默病大脑中发现GSK - 3β蛋白水平升高，且在阿尔茨海默病中GSK - 3β与PHF相关。为了解GSK - 3β活性在转录水平如何受到调控，我们分离了人GSK - 3β启动子。GSK - 3β启动子不含传统的TATA盒，不过鉴定出了其他几个转录因子结合位点。通过5' RACE确定了一个推定的转录起始位点。将各种GSK - 3β启动子CAT报告基因转染到COS - 7细胞和SHSY5Y神经细胞中，结果显示GSK - 3β启动子在神经细胞中活性更高。此类涉及启动子缺失突变体的转染研究表明，在 - 1421至 - 1363位可能存在一个负转录反应元件，在 - 427至 - 384位存在一个激活序列。启动子内也存在CP2结合位点。最近发现CP2可与阿尔茨海默病淀粉样前体蛋白结合蛋白Fe65相互作用。讨论了这些结果与阿尔茨海默病发病机制的相关性。
