Reduction of Raf-1 kinase inhibitor protein expression correlates with breast cancer metastasis.
OBJECTIVE
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. Therefore, we investigated whether RKIP expression is altered in clinical specimens of human primary breast cancers and their lymph node metastases.


METHODS
Paraffin-embedded tumor samples from 103 breast cancer patients were examined immunohistochemically for the expression of RKIP, activated ERK, and apoptosis. The specificity of the antibodies used was validated by competition experiments with purified recombinant RKIP protein.


RESULTS
RKIP expression was high in breast duct epithelia and retained to varying degrees in primary breast tumors. However, in lymph node metastases, RKIP expression was highly significantly reduced or lost (P = 0.000003). No significant correlations were observed between RKIP expression and histologic type, tumor differentiation grade, size, or estrogen receptor status.


CONCLUSIONS
This is the first study of RKIP expression in a large clinical cohort. It confirms the results of cell culture and animal studies, suggesting that in human breast cancer, RKIP is a metastasis suppressor gene whose expression must be down-regulated for metastases to develop. RKIP expression is independent of other markers for breast cancer progression and prognosis.
Hagan
Suzanne
S
Beatson Institute for Cancer Research, Signaling and Proteomics Laboratory, Glasgow, UK.
Al-Mulla
Fahd
F
Mallon
Elizabeth
E
Oien
Karin
K
Ferrier
Rhona
R
Gusterson
Barry
B
García
Jorge J Curto
JJ
Kolch
Walter
W
D000727:Androgen-Binding Protein / Q000096:biosynthesis*; D017209:Apoptosis; D001943:Breast Neoplasms / Q000378:metabolism / Q000473:pathology*; D045744:Cell Line, Tumor; D015331:Cohort Studies; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism; D005260:Female; D006801:Humans; D007150:Immunohistochemistry; D008207:Lymphatic Metastasis; D049488:Phosphatidylethanolamine Binding Protein; D010766:Phosphorylation
D000727:Androgen-Binding Protein; C511482:PEBP1 protein, human; D049488:Phosphatidylethanolamine Binding Protein; D048049:Extracellular Signal-Regulated MAP Kinases