title: Osmotic stress inhibits p70/85 S6 kinase through activation of a protein phosphatase.
abstract: While studying the stress regulation of p70/85 S6 kinase (S6K), we observed that anisomycin and UV light stimulated S6K activity, but that sorbitol inactivated S6K. Pretreatment with hyperosmotic stress also prevented the activation of S6K by both 12-O-tetradecanoylphorbol-13-acetate and anisomycin. Comparison of sorbitol and rapamycin revealed that both agents inactivated S6K and caused dephosphorylation of Ser/Thr-Pro sites in the COOH terminus of S6K, including Thr(412), a residue essential to S6K regulation, as determined by phospho-specific antibodies. Rapamycin-resistant S6K truncation mutants were similarly resistant to deactivation by sorbitol. Additionally, the PHAS-1 mobility shift, which is sensitive to rapamycin, was also found to be sensitive to osmotic stress. Experiments using the p38 inhibitor SB203580 and dominant negative mutants involving both stress-activated protein kinase/c-Jun NH(2)-terminal kinase and p38 stress pathways indicated that these pathways are probably not involved in osmotic stress inhibition of S6K. Examining the potential involvement of a phosphatase, we found that sodium pyrophosphate, sodium vanadate, cyclosporin A, tautomycin, and okadaic acid had no effect on osmotic stress inhibition of S6K. However, calyculin A prevented both rapamycin- and sorbitol-mediated deactivation of S6K. Our results suggest that osmotic stress and rapamycin act through a calyculin A-sensitive phosphatase to cause dephosphorylation and deactivation of S6K.
authors.affiliation: Institute of Pathology, Case Western Reserve University, Cleveland, Ohio 44106, USA.
authors.forename: L A
authors.initials: LA
authors.lastname: Parrott
authors.forename: D J
authors.initials: DJ
authors.lastname: Templeton
mesh_terms: D048868:Adaptor Proteins, Signal Transducing; D000818:Animals; D002352:Carrier Proteins; D018797:Cell Cycle Proteins; D002460:Cell Line; D002522:Chlorocebus aethiops; D004789:Enzyme Activation; D006801:Humans; D008387:Marine Toxins; D009154:Mutation; D009997:Osmotic Pressure; D010080:Oxazoles / Q000494:pharmacology; D010749:Phosphoprotein Phosphatases / Q000378:metabolism*; D010750:Phosphoproteins / Q000378:metabolism; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D019893:Ribosomal Protein S6 Kinases / Q000037:antagonists & inhibitors*; D020123:Sirolimus / Q000494:pharmacology; D014466:Ultraviolet Rays
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D002352:Carrier Proteins; D018797:Cell Cycle Proteins; C087000:EIF4EBP1 protein, human; D008387:Marine Toxins; D010080:Oxazoles; D010750:Phosphoproteins; C059041:calyculin A; D017346:Protein Serine-Threonine Kinases; D019893:Ribosomal Protein S6 Kinases; D010749:Phosphoprotein Phosphatases; D020123:Sirolimus