Activation of 40-kDa Protein Kinases in Response to Hypo- and Hyperosmotic Shock in the Halotolerant Green Alga Dunaliella tertiolecta

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Changes in protein kinase activities in Dunaliella tertiolecta in response to hypo- and hyperosmotic shocks were assessed by assays of protein kinase activities on SDS-poly-acrylamide gels that contained protein substrates. Hypo-osmotic shock (transfer from 0.5 to 0.2 M NaCl) transiently activated a 40-kDa protein kinase (low osmotic pressure-activated protein kinase, LAP kinase) that phosphorylated myelin basic protein (MBP) and histone H1 but not casein. By contrast, hyperosmotic shock (transfer from 0.5 to 1.1 M NaCl) rapidly activated another 40-kDa protein kinase (high osmotic pressure-activated protein kinase, HAP kinase) that phosphorylated casein and histone H1 but not MBP. Inhibitors of protein kinases, namely, K-252a and staurosporine, suppressed the activation of both LAP kinase and HAP kinase. The protein kinase activities in extracts of osmotically shocked cells disappeared completely after treatment with calf intestinal alkaline phosphatase. Anti-phosphotyrosine monoclonal antibodies did not cross-react with either LAP kinase or HAP kinase. These results indicate that at least two 40-kDa protein kinases, LAP kinase and HAP kinase, are activated by hyper- and hypoosmotic shock, respectively, and that their activities are regulated via phosphorylation by putative protein ki-nase(s) that act at an upstream position in the signaling cascade(s) that follows osmotic shock.
日本植物生理学会の論文