STRUCTURE OF MURINE AND HUMAN RENAL TYPE-II NA-PHOSPHATE COTRANSPORTER GENES (NPT2 AND NPT2)()

Na+-phosphate (Pi) cotransport across the renal brush border membrane is the rate limiting step in the overall reabsorption of filtered Pi. Murine and human renal-specific cDNAs (NaPi-7 and NaPi-3, respectively ) related to this cotransporter activity (type II Na+-Pi cotransporter ) have been cloned, We now report the cloning and characterization of the corresponding mouse (Npt2) and human (NPT2) genes. The genes were cloned by screening mouse genomic and human chromosome 5-specific libr aries, respectively. Both genes are approximately 16 kb and are compri sed of 13 exons and 12 introns, the junctions of which conform to dono r and acceptor site consensus sequences. Putative CAAT and TATA boxes are located, respectively, at positions -147 and -40 of the Npt2 gene and -143 and -51 of the NPT2 gene, relative to nucleotide 1 of the cor responding cDNAs. The translation initiation site is within exon 2 of both genes. The first 220 bp of the mouse and human promoter regions e xhibit 72% identity. Two transcription start sites (at positions -9 an d -10 with respect to nucleotide 1 of NaPi-7 cDNA) and two polyadenyly lation signals were identified in the Npt2 gene by primer extension, 5 ' and 3' rapid amplification of cDNA ends (RACE). A 484-bp 5' flanking region of the Npt2 gene, comprising the CAAT box, TATA box, and exon 1, was cloned upstream of a luciferase reporter gene; this construct s ignificantly stimulated luciferase gene expression, relative to contro ls, when transiently transfected into OK cells, a renal cell line expr essing type II Na+-Pi cotransporter activity. The present data provide a basis for detailed analysis of cis and trans elements involved in t he regulation of Npt2/NPT2 gene transcription and facilitate screening for mutations in the NPT2 gene in patients with autosomally inherited disorders of renal Pi reabsorption.