Cloning and regulation of expression of the rat kidney urea transporter (rUT2).

Abstract

In mammals, urea is the predominant end-product of nitrogen metabolism and plays a central role in the urinaryconcentrating mechanism. Urea accumulation in the renal medulla is critical to the ability of the kidney to concentrate urine to an osmolality greater than systemic plasma. Regulation of urea excretion and accumulation in the renal medulla depends on the functional state of specialized phloretin-sensitive urea transporters. To study these transporters and their regulation of expression we isolated a cDNA which encodes the rat homologue (rUT2) of rabbit UT2 (You, G., C. P. Smith, Y. Kanai, W.-S. Lee, M. Stelzner, and M. A. Hediger, et al. Nature (Lond.). 1993.365:844-847). Rat UT2 has 88% amino acid sequence identity to rabbit UT2 and 64% identity to the recently cloned human erythrocyte urea transporter, HUT1l (Olives, B., P. Neav, P. Bailly, M. A. Hediger, G. Rousselet, J. P. Cartron, and P. Ripoch J. Biol. Chem. 1994. 269:31649-31652). Analysis of rat kidney mRNA revealed two transcripts of size 2.9 and 4.0 kb which had spatially distinct distributions. Northern analysis and in situ hybridization showed that the 4.0-kb transcript was primarily responsive to changes in the protein content of the diet whereas the 2.9-kb transcript was responsive to changes in the hydration state of the animal. These studies reveal that the expression levels of the two rUT2 transcripts are modulated by different pathways to allow fluid and nitrogen balance to be regulated independently. Our data provide important insights into the regulation of the renal urea transporter UT2 and provide a basis on which to refine our understanding of the urinary concentrating mechanism and its regulation. (J. Clin. Invest. 1995. 96:1556-1563

Molecular characterization of a new urea transporter in the human kidney

“…As expected for a vasopressin-regulated transporter, UT2 is localized in the inner medullary collecting ducts and probably in the descending thin limbs of Henle's loop [9], where it plays a central role in the establishment of a corticomedullary osmotic gradient. Two transcripts (4.0 and 2.9 kb) of a rat urea transporter (rUT2) were identified in the kidney [7].…”

“…3), at the opposite of the UT2 transcript which was present in the rabbit colon [6]. Recently, it was reported that the rat UT2 transcript was undetectable in the colon and it was suggested that this may represent an adaptation towards the dietary protein consumed between herbivore (rabbit) and omnivore (rat) [7].…”

“…Thus, the plasma membrane of human erythrocytes [3,4] and some renal epithelial cells [5] exhibit an elevated urea permeability which is mediated by highly selective urea transporters. At least two forms of urea transporters have recently been identified: (i) the presumably vasopressin-sensitive rabbit and rat transporters UT2 [6,7] and (ii) the constitutive human transporter HUTll [8].…”

“…Two transcripts (4.0 and 2.9 kb) of a rat urea transporter (rUT2) were identified in the kidney [7]. They have a spatially distinct distribution and their expression is modulated by different pathways.…”

“…They have a spatially distinct distribution and their expression is modulated by different pathways. Indeed, the 4.0 kb transcript is confined to the inner medulla and is responsive to changes in the protein diet, whereas the 2.9 kb transcript is predominantly expressed in the inner stripe of the outer medulla and is responsive to the hydration state [7]. Thus, the two rUT2 The human urea transporter (HUTll clone) has been cloned by cross-hybridization from a human bone marrow library [8].…”