The control of human histidine decarboxylase gene expression and elucidation of the regulatory mechanism of histamine synthesis

以组氨酸为原料，以组氨酸脱羧酶（HDC）催化合成组胺。该HDC基因在造血细胞肥大细胞和嗜碱性细胞中表达受限。通过RNA印迹分析发现，人类肥大细胞系HMC-1表达HDC mRNA，而人类红系K562不表达HDC mRNA。流式细胞实验显示，hcc -1细胞比K562细胞转录更高的HDC mRNA。这些结果表明存在细胞系特异性的顺式作用元件调控HDC基因的转录。通过将插入荧光素酶报告基因上游的5'侧翼区多种缺失突变的质粒瞬时转染到HMC-1和K562细胞中，发现-153 bp和52 bp之间的片段是转录所必需的。在这个片段中有几个公认的转录因子结合元件。在制备更精细的缺失突变体并转染鉴定这些元件的活性后，明确了-64 bp和52 bp之间的GC盒对基础转录很重要。我们进一步评估了hmc1和K562的核蛋白与合成的包含该GC盒序列的寡核苷酸的结合活性。结果表明，在HMC-1和K562中均存在Sp1蛋白，Sp1蛋白与该片段结合，而不与GC盒突变片段结合。我们进一步寻找从转录起始位点到最后一个外显子下游3 Kb的-7 Kb之间的组织/细胞特异性增强子和/或抑制子，但尚未找到候选子。对组织/细胞特异性顺式元件进行进一步的实验研究是必然的。

Histamine is synthesized from histidine catalyzed with histidine decarboxylase (HDC). The expression of this HDC gene is restricted in mast cells and basophils in the hematopoietic cells. By RNA blot analysis it was shown that the HMC-1 which is a unique human mast cell line express HDC mRNA but K562 which is one of human erythroid cell lines does not. HMC-1 cells were shown to transcribe higher HDC mRNA than K562 cells by nuclear run-on assay. These results suggest the existence of cell lineage specific cis-acting elements for the regulation of the transcription of HDC gene. By transient transfection of the plasmids containing various deletion mutants of 5' flanking region inserted into just upstream of luciferase reporter gene into HMC-1 and K562 cells, it is suggested that the flagment between-153 bp and-52 bp is essential for the transcription. In this fragment there are several consensus binding elements for transcription factors. After preparing finer deletion mutants and transfection to descriminate the activity of those element, it was clarifiedthat GC box between-64 bp and-52 bp is important for basal transcription. We further assessed the binding activity of the nuclear protein of HMC 1 and K562 to synthetic oligonucleotide including this GC box sequence. It was proved that there are Sp1 protein in both HMC-1 and K562 which bind to this fragment but not to the GC box-mutated fragment. We further searched for tissue/cell specific enhancer and/or suppressor between-7 Kb from transcription initiation site to 3 Kb down stream of the last exon, but there are no candidates yet. It is inevitable to do further experiment to elucidate the tissue/cell specific cis-elements.