Cloning of the rat Slc14a2 gene and genomic organization of the UT-A urea transporter

We cloned the Slc14a2 gene and determined the genomic organization of the r at urea transporter UT-A. Slc14a2, the gene encoding the rat UT-A transport er, extends for more that 300 kb. The four known rat mRNA isoforms: UT-A1, UT-A2, UT-A3, and UT-A4 are transcribed from 24 exons. The Slc14a2 genomic map also accounts for 3'-untranslated sequences expressed alternatively in UT-A1, UT-A2, and UT-A3. We previously identified a TATA-less, tonicity-res ponsive promoter controlling the transcription of UT-A1, UT-A3, and UT-A4 f rom a single initiation site in the 5'-flanking region of the gene. Here, w e describe a second, internal promoter in intron 12, which controls the tra nscription of UT-A2 starting from exon 13. This region contains a TATA moti f upstream from the UT-A2 transcription start site, and shows consensus seq uences for the cAMP response element (CRE) and for the tonicity enhancer (T onE) motif. Stimulation by cAMP induces UT-A2 mRNA expression in mIMCD3 cel ls, and luciferase activity in mIMCD3 cells transfected with those pGL3 con structs including the CRE sequences. Although long-term exposure to hyperto nicity induces UT-A2 expression in mIMCD3 cells, hypertonicity does not ind uce significantly the activity of the promoter in intron 12. In summary, we describe the genomic structure of the rat UT-A urea transporter, encoded b y the Slc14a2 gene. Our findings suggest that two promoters regulate transc ription of the four UT-A isoforms, and that stimulation of transcription by vasopressin, mediated by cAMP and CRE sequences, and controlled by an intr onic promoter, may contribute to the increase in UT-A2 expression during wa ter deprivation. (C) 2001 Elsevier Science B.V. All rights reserved.