Raf kinase inhibitor protein suppresses nuclear factor-κB-dependent cancer cell invasion through negative regulation of matrix metalloproteinase expression

Cancer Lett. 2010 Dec 28;299(2):137-49. doi: 10.1016/j.canlet.2010.08.012. Epub 2010 Sep 19.


Accumulating evidence suggests that Raf kinase inhibitor protein (RKIP), which negatively regulates multiple signaling cascades including the Raf and nuclear factor-κB (NF-κB) pathways, functions as a metastasis suppressor. However, the basis for this activity is not clear. We investigated this question in a panel of breast cancer, colon cancer and melanoma cell lines. We found that RKIP negatively regulated the invasion of the different cancer cells through three-dimensional extracellular matrix barriers by controlling the expression of matrix metalloproteinases (MMPs), particularly, MMP-1 and MMP-2. Silencing of RKIP expression resulted in a highly invasive phenotype and dramatically increased levels of MMP-1 and MMP-2 expression, while overexpression of RKIP decreased cancer cell invasion in vitro and metastasis in vivo of murine tumor allografts. Knockdown of MMP-1 or MMP-2 in RKIP-knockdown cells reverted their invasiveness to normal. In contrast, when examining migration of the different cancer cells in a two-dimensional, barrier-less environment, we found that RKIP had either a positive regulatory activity or no activity, but in no case a negative one (as would be expected if RKIP suppressed metastasis at the level of cell migration itself). Therefore, RKIP's function as a metastasis suppressor appears to arise from its ability to negatively regulate expression of specific MMPs, and thus invasion through barriers, and not from a direct effect on the raw capacity of cells to move. The NF-κB pathway, but not the Raf pathway, appeared to positively control the invasion of breast cancer cells. A regulatory loop involving an opposing relationship between RKIP and the NF-κB pathway may control the level of MMP expression and cell invasion.

Publication types

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

MeSH terms

  • Animals
  • Blotting, Western
  • Cell Line, Tumor
  • Cell Movement
  • Cell Proliferation
  • Female
  • Gene Expression Regulation, Neoplastic
  • Humans
  • Mammary Neoplasms, Experimental / genetics
  • Mammary Neoplasms, Experimental / metabolism
  • Mammary Neoplasms, Experimental / pathology
  • Matrix Metalloproteinase 1 / genetics
  • Matrix Metalloproteinase 1 / metabolism
  • Matrix Metalloproteinase 2 / genetics
  • Matrix Metalloproteinase 2 / metabolism
  • Matrix Metalloproteinases / genetics
  • Matrix Metalloproteinases / metabolism*
  • Mice
  • Mice, Inbred BALB C
  • NF-kappa B / metabolism*
  • Neoplasm Invasiveness
  • Neoplasms / genetics
  • Neoplasms / metabolism*
  • Neoplasms / pathology
  • Phosphatidylethanolamine Binding Protein / genetics
  • Phosphatidylethanolamine Binding Protein / metabolism*
  • RNA Interference
  • Reverse Transcriptase Polymerase Chain Reaction
  • Signal Transduction


  • NF-kappa B
  • PEBP1 protein, human
  • Phosphatidylethanolamine Binding Protein
  • Raf kinase inhibitory protein, mouse
  • Matrix Metalloproteinases
  • Matrix Metalloproteinase 2
  • Matrix Metalloproteinase 1