Wong Wai K, Chen Kevin, Shih Jean C
Department of Cell and Neurobiology, Keck School of Medicine, University of Southern California, Los Angeles, California 90033, USA.
J Biol Chem. 2003 Sep 19;278(38):36227-35. doi: 10.1074/jbc.M305549200. Epub 2003 Jul 10.
Monoamine oxidase (MAO) A and B catalyze the oxidative deamination of neuroactive and dietary monoamines such as serotonin, tyramine, and phenylethylamine. Here we show that MAO B, but not MAO A, gene expression was induced during Caco-2 cell differentiation; thus this cell line was used as a model system to study the gene regulation unique for MAO B. Luciferase and gel shift assays showed that transcription factors Sp1 and Sp3 binding to -246 and -99 bp were responsible for the observed gene activation. Overexpression of Sp3 inhibited the induction of MAO B gene by Sp1, and the expression of Sp3 was decreased during Caco-2 cell differentiation. Computer analysis revealed a putative CpG island containing 22 potential CpG methylation sites between -261 and -58 bp. In vitro methylation of MAO B promoter with 5-aza-2'-deoxycytidine, a DNA methyltransferase inhibitor, up-regulated MAO B gene expression in both HeLa and Caco-2 cells. Sodium bisulfite sequencing showed a gradually reduced methylation of the CpG sites during Caco-2 cell differentiation. These results suggested that MAO B gene expression is selectively induced by a decreased Sp3/Sp1 ratio and reduced DNA methylation. This new information may provide insights on the tissue-specific expression of these two isoenzymes.
单胺氧化酶（MAO）A和B催化神经活性单胺和膳食单胺（如5-羟色胺、酪胺和苯乙胺）的氧化脱氨反应。在此我们表明，在Caco-2细胞分化过程中，MAO B的基因表达被诱导，而MAO A则未被诱导；因此，该细胞系被用作研究MAO B独特基因调控的模型系统。荧光素酶和凝胶迁移试验表明，与 -246和 -99 bp结合的转录因子Sp1和Sp3负责观察到的基因激活。Sp3的过表达抑制了Sp1对MAO B基因的诱导，并且在Caco-2细胞分化过程中Sp3的表达下降。计算机分析揭示了一个假定的CpG岛，在 -261和 -58 bp之间包含22个潜在的CpG甲基化位点。用DNA甲基转移酶抑制剂5-氮杂-2'-脱氧胞苷对MAO B启动子进行体外甲基化，可上调HeLa和Caco-2细胞中MAO B基因的表达。亚硫酸氢钠测序显示，在Caco-2细胞分化过程中，CpG位点的甲基化逐渐减少。这些结果表明，MAO B基因表达通过Sp3/Sp1比值降低和DNA甲基化减少而被选择性诱导。这一新信息可能为这两种同工酶的组织特异性表达提供见解。
