title: A clickable inhibitor reveals context-dependent autoactivation of p90 RSK.
abstract: p90 ribosomal protein S6 kinases (RSKs) integrate upstream signals through two catalytic domains. Autophosphorylation of Ser386 by the regulatory C-terminal kinase domain (CTD) is thought to be essential for activation of the N-terminal kinase domain (NTD), which phosphorylates multiple downstream targets. We recently reported fmk, an irreversible inhibitor of the CTD of RSK1 and RSK2. Here we describe fmk-pa, a propargylamine variant that has improved cellular potency and a 'clickable' tag for assessing the extent and selectivity of covalent RSK modification. Copper-catalyzed conjugation of an azidoalkyl reporter (the click reaction) revealed that fmk-pa achieves selective and saturable modification of endogenous RSK1 and RSK2 in mammalian cells. Saturating concentrations of fmk-pa inhibited Ser386 phosphorylation and downstream signaling in response to phorbol ester stimulation, but had no effect on RSK activation by lipopolysaccharide. RSK autoactivation by the CTD is therefore context dependent, which suggests that NTD and CTD inhibitors should have distinct physiological effects.
authors.affiliation: Program in Chemistry and Chemical Biology, and Department of Cellular and Molecular Pharmacology, University of California, San Francisco, California 94158-2280, USA.
authors.forename: Michael S
authors.initials: MS
authors.lastname: Cohen
authors.forename: Haralambos
authors.initials: H
authors.lastname: Hadjivassiliou
authors.forename: Jack
authors.initials: J
authors.lastname: Taunton
mesh_terms: D000818:Animals; D001360:Avidin / Q000096:biosynthesis / Q000235:genetics; D015153:Blotting, Western; D002460:Cell Line; D019295:Computational Biology; D015195:Drug Design; D004789:Enzyme Activation / Q000502:physiology*; D004791:Enzyme Inhibitors / Q000138:chemical synthesis* / Q000737:chemistry / Q000494:pharmacology*; D006801:Humans; D007527:Isoenzymes / Q000037:antagonists & inhibitors / Q000737:chemistry; D008070:Lipopolysaccharides / Q000494:pharmacology; D008264:Macrophages / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism; D051379:Mice; D010766:Phosphorylation; D019893:Ribosomal Protein S6 Kinases / Q000037:antagonists & inhibitors*; D013268:Stimulation, Chemical; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology
chemical_list: D004791:Enzyme Inhibitors; D007527:Isoenzymes; D008070:Lipopolysaccharides; D001360:Avidin; D019893:Ribosomal Protein S6 Kinases; D013755:Tetradecanoylphorbol Acetate