title: Raf kinase inhibitor protein suppresses nuclear factor-κB-dependent cancer cell invasion through negative regulation of matrix metalloproteinase expression.
abstract: 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.
authors.affiliation: Department of Chemistry, University of Connecticut, Storrs, CT 06269, USA.
authors.forename: Anwar B
authors.initials: AB
authors.lastname: Beshir
authors.forename: Gang
authors.initials: G
authors.lastname: Ren
authors.forename: Anniefer N
authors.initials: AN
authors.lastname: Magpusao
authors.forename: Lauren M
authors.initials: LM
authors.lastname: Barone
authors.forename: Kam C
authors.initials: KC
authors.lastname: Yeung
authors.forename: Gabriel
authors.initials: G
authors.lastname: Fenteany
mesh_terms: D000818:Animals; D015153:Blotting, Western; D045744:Cell Line, Tumor; D002465:Cell Movement; D049109:Cell Proliferation; D005260:Female; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D008325:Mammary Neoplasms, Experimental / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D020781:Matrix Metalloproteinase 1 / Q000235:genetics / Q000378:metabolism; D020778:Matrix Metalloproteinase 2 / Q000235:genetics / Q000378:metabolism; D020782:Matrix Metalloproteinases / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D008807:Mice, Inbred BALB C; D016328:NF-kappa B / Q000378:metabolism*; D009361:Neoplasm Invasiveness; D009369:Neoplasms / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D049488:Phosphatidylethanolamine Binding Protein / Q000235:genetics / Q000378:metabolism*; D034622:RNA Interference; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction
chemical_list: D016328:NF-kappa B; C511482:PEBP1 protein, human; D049488:Phosphatidylethanolamine Binding Protein; C539308:Raf kinase inhibitory protein, mouse; D020782:Matrix Metalloproteinases; D020778:Matrix Metalloproteinase 2; D020781:Matrix Metalloproteinase 1