Identification and characterization of multiple osmotic response sequences in the human aldose reductase gene

Abstract

Aldose reductase (AR) has been implicated in osmoregulation in the kidney because it reduces glucose to sorbitol, which can serve as an osmolite. Under hyperosmotic stress, transcription of this gene is induced to increase the enzyme level. This mode of osmotic regulation of AR gene expression has been observed in a number of nonrenal cells as well, suggesting that this is a common response to hyperosmotic stress. We have identified a 132-base pair sequence 1 kilobase pairs upstream of the transcription start site of the human AR gene that enhances the transcription activity of the AR promoter as well as that of the SV40 promoter when the cells are under hyperosmotic stress. Within this 132-base pair sequence, there are three sequences that resemble TonE, the tonicity response element of the canine betaine transporter gene, and the osmotic response element of the rabbit AR gene, suggesting that the mechanism of osmotic regulation of gene expression in these animals is similar. These three sequences are designated as OreA, OreB, and OreC respectively, Analysis of the mouse AR gene also revealed that these three sequences are highly conserved between the mouse and human. Results from site-directed mutagenesis and gel mobility shift assays suggested that the OreC is the most important element for the osmotic response and cooperative interaction among the three elements in the human AR gene is essential for their enhancer function. The human aldose reductase gene osmotic response elements are the first osmotic response elements characterized in human.