Dealing with osmostress through MAP kinase activation

Abstract

In response to changes in the extracellular environment, cells coordinate intracellular activities to maximize their probability of survival and proliferation. Eukaryotic cells, from yeast to mammals, transduce diverse extracellular stimuli through the cell by multiple mitogen-activated protein kinase (MAPK) cascades. Exposure of cells to increases in extracellular osmolarity results in rapid activation of a highly conserved family of MAPKs, known as stress-activated MAPKs (SAPKs). Activation of SAPKs is essential for the induction of adaptive responses required for cell survival upon osmostress. Recent studies have begun to shed light on the broad effects of SAPK activation in the modulation of several aspects of cell physiology, ranging from the control of gene expression to the regulation of cell division.

Fig. 1. Schematic diagram of the yeast HOG pathway. Pbs2 integrates signals from two major independent upstream osmosensing mechanisms, which leads to the activation of specific MAPKKKs. Under osmostress, activated Pbs2 activates the Hog1 MAPK, which induces a set of osmoadaptive responses.

Fig. 2. Mammalian SAPK pathways. The MAPKKKs upstream of JNK and p38 belong to three broad protein kinase families differentiated by colour in the figure (TAOs, MEKKs and MLKs). There are four MAPKKs with overlapping activities but with different specificity.

Fig. 3. Activation of SAPKs by osmostress has a great impact on cell physiology. In response to stress, the yeast Hog1 (upper panel) or the mammalian p38 and JNK (lower panel) induce diverse osmoadaptive responses.

Paula M. Alepuz, Francesc Posas & Eulàlia de Nadal. Francesc Posas is the recipient of an EMBO Young Investigator Award