The promoter of the human 25-hydroxyvitamin D3 1α-hydroxylase gene confers positive and negative responsiveness to PTH, calcitonin, and 1α,25(OH)2D3

25-Hydroxyvitamin D-3 1 alpha-hydroxylase (1 alpha-hydroxylase) catalyzes hydroxylation, mainly in the kidney, of 25-hydroxyvitamin D-3 [25(OH)D-3] into 1 alpha,25-dihydroxyvitamin D-3 [1 alpha,25(OH)(2)D-3], a hormonal form of vitamin D, acting as a key enzyme of vitamin D biosynthesis. Reflecting its biological significance, this enzymatic activity is differentially regulated by several factors involving calcium homeostasis, though the molecular mechanism is poorly understood. In our recent study (K. Takeyama, ct al., 1997), we cloned the cDNA of mouse 1 alpha-hydroxylase, and this led us to investigate the regulation of gene expression and the function of the promoter of this gene. Here we report the isolation of the 5' flanking region of the human 1 alpha-hydroxylase gene and the identification of the human 1 alpha-hydroxylase promoter by a primer extension assay. We found that in the identified promoter, a positively regulatory region to parathyroid hormone (PTH) and calcitonin and a negatively regulatory region to 1 alpha,25(OH)(2)D-3 are located around -4 and -0.5 kb, respectively. Thus, we provide direct evidence that the positive and negative regulation of la-hydroxylase gene expression by hormones takes place at transcriptional levels through two distinct promoter regions. (C) 1998 Academic Press.