BCR/ABL activates Rap1 and B-Raf to stimulate the MEK/Erk signaling pathway in hematopoietic cells

Biochem Biophys Res Commun. 2005 Jan 21;326(3):645-51. doi: 10.1016/j.bbrc.2004.11.086.


The BCR/ABL fusion tyrosine kinase activates various intracellular signaling pathways, thus causing chronic myeloid leukemia (CML). Here we demonstrate that the inducible expression of BCR/ABL in a murine hematopoietic cell line, TonB210, leads to the activation of the Ras family small GTPase Rap1, which is inhibited by the ABL kinase inhibitor imatinib. The Rap1 activity in a CML cell line, K562, was also inhibited by imatinib. Inhibition of Rap1 activation by a dominant negative mutant of Rap1, Rap1-N17, or SPA-1 inhibited the BCR/ABL-induced activation of Elk-1. BCR/ABL also activated in a kinase activity-dependent manner the B-Raf kinase, which is an effector molecule of Rap1 and a potent activator of the MEK/Erk/Elk-1 signaling pathway. Together, these data suggest that, in addition to the well-established Ras/Raf-1 pathway, BCR/ABL activates the alternative signaling pathway involving Rap1 and B-Raf to activate Erk, which may play important roles in leukemogenesis.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Extracellular Signal-Regulated MAP Kinases / metabolism*
  • Fusion Proteins, bcr-abl / metabolism*
  • Hematopoietic Stem Cells / metabolism
  • MAP Kinase Kinase Kinases / metabolism*
  • Mice
  • Proto-Oncogene Proteins B-raf / metabolism*
  • rac GTP-Binding Proteins / metabolism
  • rap1 GTP-Binding Proteins / metabolism*
  • ras Proteins / metabolism


  • Fusion Proteins, bcr-abl
  • Braf protein, mouse
  • Proto-Oncogene Proteins B-raf
  • Extracellular Signal-Regulated MAP Kinases
  • MAP Kinase Kinase Kinases
  • rac GTP-Binding Proteins
  • rap1 GTP-Binding Proteins
  • ras Proteins