Ontogeny of renal sulfate transporters: postnatal mRNA and protein expression

American Journal of Physiology-Cell Physiology

2004

The sat-1 transporter mediates sulfate/bicarbonate/oxalate anion exchange in vivo at the basolateral membrane of the kidney proximal tubule. In the present study, we show two renal cell lines [Madin-Darby canine kidney (MDCK) and porcine proximal tubular kidney (LLC-PK1) cells] that similarly target sat-1 exclusively to the basolateral membrane. To identify possible sorting determinants, we generated truncations of the sat-1 cytoplasmic COOH terminus, fused to enhanced green fluorescence protein (EGFP) or the human IL-2 receptor alpha-chain (Tac) protein, and both fusion constructs were transiently transfected into MDCK cells. Confocal microscopy revealed that removal of the last three residues on the sat-1 COOH terminus, a putative PDZ domain, had no effect on basolateral sorting in MDCK cells or on sulfate transport in Xenopus oocytes. Removal of the last 30 residues led to an intracellular expression for the GFP fusion protein and an apical expression for the Tac fusion protein, suggesting that a possible sorting motif lies between the last 3 and 30 residues of the sat-1 COOH terminus. Elimination of a dileucine motif at position 677/678 resulted in the loss of basolateral sorting, suggesting that this motif is required for sat-1 targeting to the basolateral membrane. This posttranslational mechanism may be important for the regulation of sulfate reabsorption and oxalate secretion by sat-1 in the kidney proximal tubule.

Section: Resultsmentioning

confidence: 90%

A dileucine motif targets the sulfate anion transporter sat-1 to the basolateral membrane in renal cell lines

Regeer

American Journal of Physiology-Cell Physiology

2004

“…However, since the total renal tubular mass and the BBM and BLM surface areas of the proximal tubule are much smaller at birth than in adulthood (75,134) and the fact that the proximal tubular segment (S1) where the majority of sulfate reabsorption occurs is poorly developed in the newborn compared with the adult (95,108,119,240), we could expect to see a reduced number of sulfate transporters in the young compared with adults. To resolve this issue, a recent study in this laboratory looked at the expression levels (mRNA and protein) of NaSi-1 and sat-1 transporters in rats of various ages (156). It was demonstrated that renal sulfate transport changed with postnatal age: both NaSi-1 and sat-1 mRNA levels increased by 10-fold (per g RNA) from day 1 to day 77 (11 wk) rats (156).…”

Section: K Pregnancy and Postnatal Growthmentioning

confidence: 99%

“…To resolve this issue, a recent study in this laboratory looked at the expression levels (mRNA and protein) of NaSi-1 and sat-1 transporters in rats of various ages (156). It was demonstrated that renal sulfate transport changed with postnatal age: both NaSi-1 and sat-1 mRNA levels increased by 10-fold (per g RNA) from day 1 to day 77 (11 wk) rats (156). A similar age-dependent increase was observed for sodium-dependent and sodium-independent sulfate uptakes in Xenopus oocytes injected with kidney mRNAs from rats of increasing age.…”

Section: K Pregnancy and Postnatal Growthmentioning

confidence: 99%

Physiological Roles and Regulation of Mammalian Sulfate Transporters

2001

Physiological Reviews

244

All cells require inorganic sulfate for normal function. Sulfate is among the most important macronutrients in cells and is the fourth most abundant anion in human plasma (300 microM). Sulfate is the major sulfur source in many organisms, and because it is a hydrophilic anion that cannot passively cross the lipid bilayer of cell membranes, all cells require a mechanism for sulfate influx and efflux to ensure an optimal supply of sulfate in the body. The class of proteins involved in moving sulfate into or out of cells is called sulfate transporters. To date, numerous sulfate transporters have been identified in tissues and cells from many origins. These include the renal sulfate transporters NaSi-1 and sat-1, the ubiquitously expressed diastrophic dysplasia sulfate transporter DTDST, the intestinal sulfate transporter DRA that is linked to congenital chloride diarrhea, and the erythrocyte anion exchanger AE1. These transporters have only been isolated in the last 10-15 years, and their physiological roles and contributions to body sulfate homeostasis are just now beginning to be determined. This review focuses on the structural and functional properties of mammalian sulfate transporters and highlights some of regulatory mechanisms that control their expression in vivo, under normal physiological and pathophysiological states.

“…FREAC-4 is regulated by Ets-1, another kidney-expressed transcription factor [7] for which there are seven potential binding sites in the NAS1 promoter. The presence of such putative binding sites in the NAS1 promoter correlates well with developmental expression of rNaSi-1 mRNA, which is up-regulated in the first 2 weeks of life [34]. rNaSi-1 mRNA and protein levels are lower in aged than in young rats and increase significantly in adult and aged rats following treatment with growth hormone [56].…”

Section: Discussionmentioning

confidence: 99%

Characterization of the human renal Na+-sulphate cotransporter gene (NAS1) promoter

Lee

Pflugers Arch - Eur J Physiol

2004

Sulphate (SO(4)(2-)) plays an essential role during growth, development, and cellular metabolism. Recently, we have isolated the human renal Na(+)-SO(4)(2-) cotransporter (hNaSi-1) that is implicated in the regulation of serum SO(4)(2-) levels. To gain an insight into hNaSi-1 regulation, our aims were to clone and characterize functionally the hNaSi-1 gene ( NAS1) promoter. We PCR-amplified 3742 bp of the NAS1 5'-flanking region, which is 64% AT-rich and contains numerous putative cis-acting elements. The NAS1 transcription start site was mapped to 25 bp upstream from the translation start site. NAS1 promoter truncations fused to luciferase gene constructs transfected into renal LLC-PK1, MDCK and OK cells allowed us to establish that the first 169 bp of the NAS1 promoter are sufficient for basal transcription. Furthermore, the NAS1 promoter conferred responsiveness to the polycyclic aromatic hydrocarbon 3-methylcholanthrene (3-MC), but not to thyroid hormone (T(3)) or vitamin D [1,25-(OH)(2)D(3)]. Site-directed mutagenesis of the NAS1 promoter identified a functional xenobiotic response element at -2,052, which conferred 3-MC responsiveness. The human NAS1 gene promoter is not responsive to Vitamin D or T(3), unlike the mouse Nas1 promoter with which it shares approximately 40% sequence similarity, but is transactivated by 3-MC, suggesting that the control of renal SO(4)(2-) reabsorption via the regulation of NAS1 transcription may be important for maintaining the sulphation potential for kidney polycyclic aromatic hydrocarbon metabolism.