Evolution of osmotic stress signaling via map kinase cascades

Cells respond to changes in osmotic pressure with compensatory molecular ad aptations that allow them to reestablish homeostasis of osmotically disturb ed aspects of cell structure and function, In addition, some cell types res pond to osmotic stress by changing their phenotype or, if their tolerance t hreshold is exceeded, by initiating programmed cell death, To understand ho w cells achieve these different types of adaptive response to osmotic stres s, it is necessary to identify the key elements of osmosensory signal trans duction and to analyze the complex networks that process osmotic stimuli im posed upon cells by their environment. This review highlights mitogen-activ ated protein kinase (MAPK) cascades as important intracellular signal-trans duction pathways activated in response to changes in osmolality, A unifying theme of osmotic stress signaling via MAPKs seems to be regulation of the cell cycle as part of the cellular stress response. This very important phy siological capacity may have been conserved throughout evolution as a major function of MAPKs from many different subfamilies. The evidence for this c onjecture is discussed, and our current knowledge about osmotic stress sign aling pathways in yeast, animals and plants is briefly reviewed.