
<ArticleTitle>Hyperosmotic stress activates the <prot>insulin receptor</prot> in CHO cells.</ArticleTitle>
<AbstractText>Stress factors, such as osmotic stress and genotoxic agents, activate stress kinases, whereas growth factors preferentially stimulate the structurally homologous mitogen-activated protein kinases, <prot>ERK1/2</prot>. Hyperosmolarity also has insulin-mimicking action as reflected by <prot>ERK1/2</prot> activation and by the stimulation of glucose uptake in adipocytes. We examined to what extent hyperosmolarity activates components of the <prot>insulin receptor</prot> (<prot>IR</prot>) signalling pathway. CHO cells expressing the human <prot>IR</prot> were treated with 500 mM NaCl or 700 mM sorbitol and the activation of insulin signalling intermediates was studied. Hyperosmolarity induced tyrosine phosphorylation of the <prot>IR</prot> beta-subunit, and the adaptor proteins <prot>p52-Shc</prot>, <prot>p66-Shc</prot>, and <prot>IRS1</prot>. Furthermore, the stress kinases <prot>JNK</prot> and <prot>p38</prot> were activated. When CHO cells were transfected with a kinase-dead <prot>IR</prot> (K1030R) mutant, hyperosmolarity did not induce tyrosine phosphorylation of the <prot>IR</prot>, indicating that hyperosmolarity induced <prot>IR</prot> autophosphorylation directly, rather than inducing phosphorylation by an exogenous tyrosine kinase. A partially purified and detergent-solubilized <prot>IR</prot> was not phosphorylated in response to hyperosmolarity, suggesting that hyperosmolarity activates the receptor only when present in the plasma membrane. In cells stably expressing the kinase-dead <prot>IR</prot>, <prot>IRS1</prot> and <prot>Shc</prot> Tyr phosphorylation was abrogated, indicating that the hyperosmolarity signalling was dependent on an active <prot><prot>IR</prot> tyrosine kinase</prot>. In contrast, the stress kinases <prot>p38</prot> and <prot>JNK</prot> were normally activated by hyperosmolarity in the <prot>IR</prot>-K1030R mutant. We conclude that, at least in CHO cells, hyperosmolarity signals partially through <prot>IR</prot> autophosphorylation and subsequent activation of the <prot>IR</prot> downstream targets. This may be responsible for some of the insulin-mimicking effects of hyperosmolarity. The activation of stress kinases by hyperosmolarity occurs independent of the <prot>IR</prot>.</AbstractText>
