Kuramasu A, Saito H, Suzuki S, Watanabe T, Ohtsu H
Department of Cellular Pharmacology, Tohoku University School of Medicine, 2-1, Seiryo-machi, Aoba-ku, Sendai 980-8575, Japan.
J Biol Chem. 1998 Nov 20;273(47):31607-14. doi: 10.1074/jbc.273.47.31607.
L-Histidine decarboxylase (HDC) catalyzes the formation of histamine from L-histidine, and in hematopoietic cell lineages the gene is expressed only in mast cells and basophils. We attempted here to discover how HDC gene expression is restricted in these cells. In the cultured cell lines tested, only the mast cells and basophils strongly transcribed the HDC gene. However, in transient transfection analysis, the reporter constructs with the HDC promoter were active not only in expressing cells but also in nonexpressing cells. Detailed analyses of the HDC promoter region revealed that the GC box is essential for transactivation. Also, the promoter region of the HDC gene proved to be sensitive to DNase I and restriction endonucleases exclusively in HDC-expressing cells, suggesting that the promoter region is readily accessible to trans-acting factor(s). Furthermore, the promoter region in HDC-expressing cell lines was found to be selectively unmethylated. The correlation between HDC expression and hypomethylation was also found in primary human mast cells. Methylation of the HDC promoter in vitro reduced the luciferase reporter activity in transient expression analysis, suggesting that methylation of the promoter region is functionally important for HDC gene expression. These results imply that alteration of DNA methylation is one of the mechanisms regulating cell-specific expression of the HDC gene.
L-组氨酸脱羧酶（HDC）催化L-组氨酸生成组胺，在造血细胞谱系中，该基因仅在肥大细胞和嗜碱性粒细胞中表达。我们在此试图探究HDC基因表达在这些细胞中是如何受到限制的。在所测试的培养细胞系中，只有肥大细胞和嗜碱性粒细胞能强烈转录HDC基因。然而，在瞬时转染分析中，带有HDC启动子的报告基因构建体不仅在表达细胞中具有活性，在非表达细胞中也具有活性。对HDC启动子区域的详细分析表明，GC盒对于反式激活至关重要。此外，HDC基因的启动子区域仅在HDC表达细胞中对DNase I和限制性内切酶敏感，这表明该启动子区域易于被反式作用因子作用。此外，在HDC表达细胞系中发现启动子区域选择性地未甲基化。在原代人肥大细胞中也发现了HDC表达与低甲基化之间的相关性。在瞬时表达分析中，体外HDC启动子的甲基化降低了荧光素酶报告基因的活性，这表明启动子区域的甲基化对HDC基因表达在功能上很重要。这些结果表明，DNA甲基化的改变是调节HDC基因细胞特异性表达的机制之一。
