AN OSMOSENSING SIGNAL-TRANSDUCTION PATHWAY IN MAMMALIAN-CELLS

The osmotic balance between the cytoplasmic and extracellular compartm ents of cells is critical for the control of cell volume. A mammalian protein kinase, Jnk, which is a distant relative of the mitogen-activa ted protein kinase group, was activated by phosphorylation on threonin e and tyrosine in osmotically shocked cells. The activation of Jnk may be relevant to the biological response to osmotic shock because the e xpression of human Jnk in the yeast Saccharomyces cerevisiae rescued a defect in growth on hyper-osmolar media. These data indicate that rel ated protein kinases may mediate osmosensing signal transduction in ye ast and mammalian cells.