RKIP downregulates B-Raf kinase activity in melanoma cancer cells

Oncogene. 2005 May 12;24(21):3535-40. doi: 10.1038/sj.onc.1208435.


The Raf-MEK-ERK protein kinase cascade is a highly conserved signaling pathway that is pivotal in relaying environmental cues from the cell surface to the nucleus. Three Raf isoforms, which share great sequence and structure similarities, have been identified in mammalian cells. We have previously identified Raf kinase inhibitor protein (RKIP) as a negative regulator of the Raf-MEK-ERK signaling pathway by specifically binding to the Raf-1 isoform. We show here that RKIP also antagonizes kinase activity of the B-Raf isoform. Yeast two-hybrid and coimmunoprecipitation experiments indicated that RKIP specifically interacted with B-Raf. Ectopic expression of RKIP antagonized the kinase activity of B-Raf. We showed that the effects of RKIP on B-Raf functions were independent of its known inhibitory action on Raf-1. The expression levels of RKIP in melanoma cancer cell lines are low relative to primary melanocytes. Forced expression of RKIP partially reverted the oncogenic B-Raf kinase-transformed melanoma cancer cell line SK-Mel-28. The low expression of RKIP and its antagonistic action on B-Raf suggests that RKIP may play an important role in melanoma turmorgenesis.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Androgen-Binding Protein / pharmacology*
  • Down-Regulation
  • Gene Expression Regulation, Neoplastic*
  • Humans
  • Melanocytes / physiology
  • Melanoma / genetics*
  • Melanoma / pathology*
  • Phosphatidylethanolamine Binding Protein
  • Proto-Oncogene Proteins B-raf / biosynthesis
  • Proto-Oncogene Proteins B-raf / pharmacology*
  • Saccharomyces cerevisiae / genetics
  • Signal Transduction
  • Skin Neoplasms / genetics*
  • Skin Neoplasms / pathology*
  • Tumor Cells, Cultured


  • Androgen-Binding Protein
  • PEBP1 protein, human
  • Phosphatidylethanolamine Binding Protein
  • BRAF protein, human
  • Proto-Oncogene Proteins B-raf