A MEK-independent role for CRAF in mitosis and tumor progression

Nat Med. 2011 Nov 13;17(12):1641-5. doi: 10.1038/nm.2464.


RAF kinases regulate cell proliferation and survival and can be dysregulated in tumors. The role of RAF in cell proliferation has been linked to its ability to activate mitogen-activated protein kinase kinase 1 (MEK) and mitogen-activated protein kinase 1 (ERK). Here we identify a MEK-independent role for RAF in tumor growth. Specifically, in mitotic cells, CRAF becomes phosphorylated on Ser338 and localizes to the mitotic spindle of proliferating tumor cells in vitro as well as in murine tumor models and in biopsies from individuals with cancer. Treatment of tumors with allosteric inhibitors, but not ATP-competitive RAF inhibitors, prevents CRAF phosphorylation on Ser338 and localization to the mitotic spindle and causes cell-cycle arrest at prometaphase. Furthermore, we identify phospho-Ser338 CRAF as a potential biomarker for tumor progression and a surrogate marker for allosteric RAF blockade. Mechanistically, CRAF, but not BRAF, associates with Aurora kinase A (Aurora-A) and Polo-like kinase 1 (Plk1) at the centrosomes and spindle poles during G2/M. Indeed, allosteric or genetic inhibition of phospho-Ser338 CRAF impairs Plk1 activation and accumulation at the kinetochores, causing prometaphase arrest, whereas a phospho-mimetic Ser338D CRAF mutant potentiates Plk1 activation, mitosis and tumor progression in mice. These findings show a previously undefined role for RAF in tumor progression beyond the RAF-MEK-ERK paradigm, opening new avenues for targeting RAF in cancer.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Animals
  • Aurora Kinase A
  • Aurora Kinases
  • Cell Cycle
  • Cell Cycle Proteins / metabolism
  • Cell Line, Tumor
  • Cell Proliferation
  • Centrosome / metabolism
  • Disease Models, Animal
  • Female
  • Humans
  • Kinetochores / metabolism
  • MAP Kinase Kinase 1 / genetics
  • MAP Kinase Kinase 1 / metabolism*
  • Mice
  • Mice, Nude
  • Mitosis*
  • Neoplasms / pathology*
  • Phosphorylation
  • Protein Serine-Threonine Kinases / metabolism
  • Proto-Oncogene Proteins / metabolism
  • Proto-Oncogene Proteins c-raf / genetics
  • Proto-Oncogene Proteins c-raf / metabolism*
  • Signal Transduction
  • Spindle Apparatus / metabolism


  • Cell Cycle Proteins
  • Proto-Oncogene Proteins
  • AURKA protein, human
  • Aurka protein, mouse
  • Aurora Kinase A
  • Aurora Kinases
  • Protein Serine-Threonine Kinases
  • Proto-Oncogene Proteins c-raf
  • polo-like kinase 1
  • MAP Kinase Kinase 1