Functional consensus for mammalian osmotic response elements

The molecular mechanisms underlying adaptation to hyperosmotic stress throu gh the accumulation of organic osmolytes are largely unknown. Yet, among or ganisms, this is an almost universal phenomenon. In mammals, the cells of t he renal medulla are uniquely exposed to high and variable salt concentrati ons; in response, renal cells accumulate the osmolyte sorbitol through incr eased transcription of the aldose reductase (AR) gene. In cloning the rabbi t AR gene, we found the first evidence of an osmotic response region in a e ukaryotic gene. More recently, we functionally defined a minimal essential osmotic response element (ORE) having the sequence CGGAAAATCAC(C) (bp -1105 to -1094). In the present study, we systematically replaced each base with every other possible nucleotide and tested the resulting sequences individ ually in reporter gene constructs. Additionally, we categorized hyperosmoti c response by electrophoretic mobility shift assays of a 17-bp sequence (-1 108 to -1092) containing the native ORE as a probe against which the test c onstructs would compete for binding. In this manner, binding activity was a ssessed for the full range of osmotic responses obtained. Thus we have arri ved at a functional consensus for the mammalian ORE, NGGAAAWDHMC(N). This f inding should accelerate the discovery of genes previously unrecognized as being osmotically regulated.