MITOGEN-ACTIVATED PROTEIN-KINASE CASCADES AND THE SIGNALING OF HYPEROSMOTIC STRESS TO IMMEDIATE-EARLY GENES

Among prokaryotes and lower eukaryotes, the threat of exposure to hype rosmotic stress is ubiquitous. Among higher eukaryotes, in contrast, o nly specific tissues are routinely exposed to marked hypertonicity. Th e mammalian renal medulla, the prototypical example, is continually su bjected to an elevated solute concentration as a consequence of the re nal concentrating mechanism. Until recently, the investigative focus h as concerned the effects of diverse solutes on the regulation of genes essential for the adaptive accumulation of osmotically active organic solutes. Recent and sweeping developments elucidating the molecular m echanisms underlying stress signaling to the nucleus have focused inte rest on earlier events in the response to hyperosmotic stress. Such ev ents include the transcriptional activation and post-translational mod ification of transcriptional activating proteins, a large subset of wh ich represent the protein products of so-called immediate early genes. This review highlights developments in the understanding of stress si gnaling in general and hypertonic stress signaling in particular in bo th yeast and higher eukaryotic models. The relationship between hypero smotic stress signaling and the transcription and activation of immedi ate-early gene transcription factors is explored. (C) 1997 Elsevier Sc ience Inc.