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A clickable inhibitor reveals context-dependent autoactivation of p90 RSK

Michael S Cohen1, Haralambos Hadjivassiliou, Jack Taunton

  • 1Program in Chemistry and Chemical Biology, and Department of Cellular and Molecular Pharmacology, University of California, San Francisco, California 94158-2280, USA.

Nature Chemical Biology
|January 30, 2007
PubMed

Insights

p90 ribosomal protein S6 kinases (RSKs) are crucial signaling enzymes. A new inhibitor, fmk-pa, selectively targets RSK1/2, revealing context-dependent activation crucial for distinct cellular responses.

Area of Science:

  • Molecular Biology
  • Cell Signaling
  • Biochemistry

Background:

  • p90 ribosomal S6 kinases (RSKs) are key regulators of cellular signaling pathways.
  • RSKs possess two catalytic domains: the N-terminal kinase domain (NTD) and the C-terminal kinase domain (CTD).
  • Autophosphorylation of Ser386 by the CTD is believed to be critical for NTD activation and downstream substrate phosphorylation.

Purpose of the Study:

  • To develop a more potent and traceable inhibitor of RSK1 and RSK2.
  • To investigate the context-dependent activation of RSKs using a novel chemical probe.
  • To determine the physiological consequences of selective RSK CTD inhibition.

Main Methods:

  • Synthesis and characterization of fmk-pa, a propargylamine variant of the RSK inhibitor fmk.
  • Utilizing click chemistry for copper-catalyzed conjugation of an azidoalkyl reporter to assess RSK modification.
  • Treatment of mammalian cells with fmk-pa and subsequent analysis of RSK phosphorylation and signaling in response to different stimuli (phorbol ester and lipopolysaccharide).

Main Results:

  • fmk-pa demonstrated improved cellular potency and enabled selective, saturable covalent modification of endogenous RSK1 and RSK2.
  • Inhibition of Ser386 phosphorylation and downstream signaling by fmk-pa was observed upon phorbol ester stimulation.
  • RSK activation induced by lipopolysaccharide remained unaffected by fmk-pa treatment, indicating stimulus-specific RSK activation mechanisms.

Conclusions:

  • RSK autoactivation via the CTD is context-dependent, varying with the upstream stimulus.
  • Selective inhibition of the RSK CTD by fmk-pa provides a tool to dissect RSK signaling pathways.
  • The distinct physiological effects of NTD and CTD inhibitors suggest differential therapeutic potential.

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