Characterization of the human Glvr-1 phosphate transporter/retrovirus receptor gene and promoter region

The cell surface receptor for gibbon ape leukemia virus (Glvr-1) belongs to the type III sodium-dependent phosphate transporter/retrovirus receptor ge ne family. Several observations have suggested an important role for Glvr-1 in regulated Pi handling in bone forming cells and prompted us to investig ate further the molecular mechanisms regulating Glvr-1 gene expression. In addition, the regulation of Glvr-1 gene expression also has potential appli cations to gene therapy, since retroviral vectors carrying gibbon ape leuke mia virus envelope proteins are used for gene delivery into different cell types. The aim of this study was thus to clone the human Glvr-1 gene in ord er to describe its structure and its promoter region. Our results indicate that the Glvr-1 gene consists of 11 exons and 10 intro ns spread over 18 kb of genomic DNA. The translation initiation site is loc ated within exon II and the translation stop codon within exon XI. Rapid am plification of cDNA ends (5'-RACE) suggests that, in human SaOS-2 osteoblas t-like cells, transcription of Glvr-1 is initiated at multiple sites, mostl y located between bp 32 and 50 of the published cDNA sequence, which was in itially obtained from HL-60 cells. The 5'-flanking region of the gene is ch aracterized by a very high GC content. Reporter gene assays demonstrate the presence of a functional promoter upstream of exon I and indicate that a G C-rich region, containing two potential SP1 binding sites, is required for high promoter activity in transiently transfected SaOS-2 cells. The description of the human Glvr-1 gene structure, as well as the analysis of some structural and functional characteristics of its promoter region, provide a basis for more detailed investigation of the molecular mechanisms controlling expression of the Glvr-1 gene in bone forming cells and in oth er cell types. (C) 1999 Elsevier Science B.V. All rights reserved.