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

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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.