Davis Warren
Medical University of South Carolina, 173 Ashley Avenue, BSB 358, MSC 505, Charleston, SC, 29403, USA.
Curr Alzheimer Res. 2015;12(9):847-59. doi: 10.2174/156720501209151019105834.
The ATP-binding cassette transporter-2 (ABCA2) is a member of a family of multipass transmembrane proteins that use the energy of ATP hydrolysis to transport substrates across membrane bilayers. ABCA2 has also been genetically linked with Alzheimer's disease but the molecular mechanisms are unknown. In this report, we hypothesized that ABCA2 modulation of sphingolipid metabolism activates a signaling pathway that regulates amyloid precursor protein transcription. We found that ABCA2 overexpression in N2a cells was associated with increased mass of the sphingolipid sphingosine, derived from the catabolism of ceramide. ABCA2 overexpression increased in vitro alkaline and acid ceramidase activity. Sphingosine is a physiological inhibitor of protein kinase C (PKC) activity. Pharmacological inhibition of ceramidase activity or activation PKC activity with 12-myristate 13-acetate (PMA) or diacylglycerol (DAG) decreased endogenous APP mRNA levels in ABCA2 overexpressing cells. Treatment with PMA also decreased the expression of a transfected human APP promoter reporter construct, while treatment with a general PKC inhibitor, GF109203x, increased APP promoter activity. In N2a cells, chromatin immunoprecipitation experiments revealed that a repressive complex forms at the AP-1 site in the human APP promoter, consisting of c-jun, c-jun dimerization protein 2 (JDP2) and HDAC3 and this complex was reduced in ABCA2 overexpressing cells. Activation of the human APP promoter in A2 cells was directed by the upstream stimulatory factors USF-1 and USF-2 that bound to an E-box element in vivo. These findings indicate that ABCA2 overexpression modulates sphingosine levels and regulates transcription of the endogenous APP gene.
ATP结合盒转运蛋白2（ABCA2）是多跨膜蛋白家族的成员，该家族利用ATP水解产生的能量跨膜双层转运底物。ABCA2在基因上也与阿尔茨海默病相关，但分子机制尚不清楚。在本报告中，我们假设ABCA2对鞘脂代谢的调节激活了一条调节淀粉样前体蛋白转录的信号通路。我们发现，N2a细胞中ABCA2的过表达与神经酰胺分解代谢产生的鞘脂鞘氨醇质量增加有关。ABCA2的过表达增加了体外碱性和酸性神经酰胺酶活性。鞘氨醇是蛋白激酶C（PKC）活性的生理抑制剂。用12-肉豆蔻酸13-乙酸酯（PMA）或二酰甘油（DAG）对神经酰胺酶活性进行药理抑制或激活PKC活性，可降低ABCA2过表达细胞中内源性APP mRNA水平。用PMA处理也降低了转染的人APP启动子报告基因构建体的表达，而用一般的PKC抑制剂GF109203x处理则增加了APP启动子活性。在N2a细胞中，染色质免疫沉淀实验表明，在人APP启动子的AP-位点形成了一种抑制复合物，该复合物由c-jun、c-jun二聚化蛋白2（JDP2）和HDAC3组成，在ABCA2过表达细胞中这种复合物减少。A2细胞中人APP启动子的激活由上游刺激因子USF-1和USF-2介导，它们在体内与一个E-box元件结合。这些发现表明，ABCA2过表达调节鞘氨醇水平并调节内源性APP基因的转录。
