Reduction of Raf-1 kinase inhibitor protein expression correlates with breast cancer metastasis.

Purpose: Raf-1 kinase inhibitor protein (RKIP) was originally identified as the first physiologic inhibitor of the Raf/mitogen-activated protein kinase kinase/extracellular signal-regulated kinase (ERK) pathway. This pathway regulates fundamental cellular functions, including those that are subverted in cancer cells, such as proliferation, transformation, survival, and metastasis. Recently, RKIP has been recognized as a strong candidate for a metastasis suppressor gene in cell and animal model systems.