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

Abstract: 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 “InsP8”) 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 °C, or heated to 42 °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 °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. [Copyright &y& Elsevier]