Transcriptional activation of the human hematopoietic prostaglandin D synthase gene in megakaryoblastic cells. Roles of the oct-1 element in the 5'-flanking region and the AP-2 element in the untranslated exon 1

The human hematopoietic prostaglandin D synthase (H-PGDS) gene is highly expressed in human megakaryoblastic cells, in which phorbol ester induces its expression. We characterized the promoter activity of the 5'-flanking region and the untranslated exon 1 (-1044 to +290) of the human H-PGDS gene in human megakaryoblastic Dami cells. Transient expression analysis using the luciferase reporter gene revealed that the 5'-flanking region and the untranslated exon 1 were sufficient for efficient expression of the H-PGDS gene in Dami cells, but not in monocytic U937 cells. Deletion and site-directed mutagenesis of the Oct-1 element in the 5'-flanking region decreased the promoter activity by approximately 30% compared with that of the entire region from -1044 to +290. An electrophoretic mobility shift assay demonstrated that Oct-1 specifically bound to the promoter region. Interestingly, even only untranslated exon 1 (+1 to +290) showed approximately 60% of the promoter activity of the entire region from -1044 to +290. Site-directed mutagenesis of the AP-2 element within the untranslated exon 1 abolished the basal promoter activity as well as its phorbol ester-mediated up-regulation. In AP-2-deficient HepG2 cells, the H-PGDS promoter activity was enhanced by coexpression with AP-2alpha. These findings indicate that the Oct-1 element in the 5'-flanking region acts as a positive cis-acting element and that the AP-2 element in the untranslated exon 1 is crucial for both basal and phorbol ester-mediated up-regulation of human H-PGDS gene expression in megakaryoblastic Dami cells.     

Isolation and characterization of the human CLC-5 chloride channel gene promoter

The human CLC-5 chloride channel is expressed mainly in the kidney and its mutations cause Dent's disease (a familial renal tubular syndrome with hypercalciuria, tubular proteinuria, rickets, nephrocalcinosis, and eventual renal failure). To gain insight into the regulatory mechanism of CLC-5 expression, a genomic clone that contains the 5'-flanking region of the human CLC-5 gene was isolated and characterized. Two types of 5'-ends of cDNA were isolated by 5'-rapid amplification of cDNA ends, and one of them, approximately 2.1 kbp upstream of ATG-containing exon II, was first identified in human. The major promoter activity was detected in the 5'-flanking region of this newly identified exon Ia. The sequence of the proximal 5'-flanking region contained an activator protein (AP)-1-like site and cAMP-responsive element, but it lacked a TATA box, a GC-rich element, and an SP-1 site. Deletion analysis of the 5'-flanking region showed that the fragments containing the AP-1-like element (TGACTCC) positioned at -38 exhibited high promoter activities in CLC-5 expressing LLC-PK1 cells, but that further deletions not containing this AP-1-like element resulted in a great loss of luciferase activities. Gel-retardation analysis demonstrated the existence of a specific protein binding to this AP-1-like element in LLC-PK1 cells, which seemed to differ from an authentic AP-1. This study clarified the key element of the human CLCN5 promoter, and the mutation in this region could be the cause of Dent's disease.