Signal transduction during environmental stress:: InsP8 operates within highly restricted contexts

Genetic manipulation of diphosphoinositol polyphosphate synthesis impacts many biological processes (reviewed in S.B. Shears, Biochem. J. 377, 2004, 265-280). These observations lacked a cell-signalling context, until the recent discovery that bis-diphosphoinositol tetrakisphosphate ([PP](2)-InSP4 or "InsP(8)") accumulates rapidly in mammalian cells in response to hyperosmotic stress (X. Pesesse, K. Choi, T. Zhang, and S. B. Shears J. Biol. Chem. 279, 2004, 43378-43381). We now investigate how widely applicable is this new stress-response. [PP](2)-InSP4 did not respond to mechanical strain or oxidative stress in mammalian cells. Furthermore, despite tight conservation of many molecular stress responses across the phylogenetic spectrum, we show that cellular [PP](2)-InSP4 levels do not respond significantly to osmotic imbalance, heat stress and salt toxicity in Saccharomyces cerevisiae. In contrast, we show that [PP](2)-InSP4 is a novel sensor of mild thermal stress in mammalian cells: [PP](2)-InSP4 levels increased 3-4 fold when cells were cooled from 37 to 33 degrees C, or heated to 42 degrees C. Increases in [PP](2)-InSP4 levels following heat-shock were evident < 5 min, and reversible (t(1/2)= 7 min) once cells were returned to 37 degrees C. These responses were blocked by pharmacological inhibition of the ERK/MEK pathway. Additional control processes may lie upstream Of [PP](2)-InSP4 synthesis, which was synergistically activated when heat stress and osmotic stress were combined. Our data add to the repertoire of signaling responses following thermal challenges, a topic of current interest for its possible therapeutic value. Published by Elsevier Inc.