Effect of SB 203580 on the activity of c-Raf in vitro and in vivo

Clare A. Hall-Jackson (Lead / Corresponding author), Michel Goedert, Philip Hedge, Philip Cohen

    Research output: Contribution to journalArticlepeer-review

    139 Citations (Scopus)


    The inhibition of SAPK2a/p38 (a mitogen activated protein (MAP) kinase family member) by SB 203580 depends on the presence of threonine at residue 106. Nearly all other protein kinases are insensitive to this drug because a more bulky residue occupies this site. Raf is one of the few protein kinases that possesses threonine at this position, and we show that SB 203580 inhibits c-Raf with an IC50 of 2 μM in vitro. However, SB 203580 does not suppress either growth factor or phorbol ester-induced activation of the classical MAP kinase cascade in mammalian cells. One of the reasons for this is that SB 203580 also triggers a remarkable activation of c-Raf in vivo (when measured in the absence of the drug). The SB203580-induced activation of c-Raf occurs without any increase in the GTP-loading of Ras, is not prevented by inhibitors of the MAPK cascade, protein kinase C or phosphatidylinositide 3-kinase, and is not triggered by the binding of this drug to SAPK2a/p38. The paradoxical activation of c-Raf by SB 203580 (and by another structurally unrelated c-Raf inhibitor) suggests that inhibitors of the kinase activity of c-Raf may not be effective as anti-cancer drugs.

    Original languageEnglish
    Pages (from-to)2047-2054
    Number of pages8
    Issue number12
    Publication statusPublished - 25 Mar 1999


    • c-Raf
    • EGF
    • MAP kinase
    • p38
    • SAPK2
    • SB203580

    ASJC Scopus subject areas

    • Molecular Biology
    • Genetics
    • Cancer Research


    Dive into the research topics of 'Effect of SB 203580 on the activity of c-Raf in vitro and in vivo'. Together they form a unique fingerprint.

    Cite this