Elucidation of the control mechanism of transcription of human L-histidine decarboxylase and trial of the control of histamine production

点击翻译按钮获取中文摘要

Since we cloned human L-histidine decarboxylase (HDC) gene in 1994, we have been investigating the control mechanism of cell specific transcription of this gene. This enzyme catalyze to produce histamine from histidine and its expressions are restricted to mast cells and basophils in hematopoietic cell lineages. We clarified here the cell specific expression in cell lines and this specificity were controlled at transcriptional level. However, in transient transfection analysis, the reporter constructs with HDC promoter were active not only in cells expressing the endogenous gene but also in non-expressing cells. Detailed analyzes of the HDC promoter region revealed that a GC box is essential for transactivation. Also, the promoter region of 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) in those cells. Furthermore, Southern blot analysis with HpaII and MspI endonucleases and sodium bisulfite analysis of genomic DNA revealed the promoter region in HDC expressing cell lines to be selectively unmethylated. In addition, 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. We provided proof that chromosomal configuration and methylation of the HDC promoter are important for mast-cell and basophil specific expression. It will be exciting to elucidate the mechanism how the chromatin structure or the mehtylation state changes during cell differentiation and/or induction. These experiments also may lead to clarify the demethylation mechanism itself. Our current efforts are focused on these points.