Identification and characterization of a metastasis suppressor gene in prostate cancer metastasis.

Metastasis suppressor genes (MSGs) inhibit the ability of cancer cells to successfully complete the complex metastatic cascade. Loss of MSGs confers the metastatic phenotype on cancer cells; however, very few MSGs have been identified to date and for most of those, their function is unknown. To identify MSGs in prostate cancer skeletal metastases, we compared gene expression between a non-metastatic prostate cancer cell line and its derivative metastatic cell line using gene array. Of the 1,176 genes screened, 35 were differentially expressed between these two cell lines. These genes are primarily involved in motility, metabolism, signal transduction, tumorigenesis and apoptosis. Among those, Raf kinase inhibitor protein (RKIP), an inhibitor of Raf-mediated MEK phosphorylation, was down-regulated in the metastatic prostate cancer cell line compared to the non-metastatic cell line. Immunchistochemistry of tissues from patients revealed RKIP expression in normal prostate and primary prostate cancers; however, RKIP expression was undetectable in all metastases examined. Stable transfection of a metastatic prostate cancer cell line with RKIP decreased in vitro invasion, without affecting proliferation rate; whereas stable transfection of a non-metastatic cell line with RKIP anti-sense increased in vitro invasion. Consistent with this finding, treatment of metastatic cancer cells with a MAP kinase inhibitor, but not other kinase inhibitors, diminished in vitro invasion. RKIP overexpression in metastatic prostate cancer cells reduced spontaneous lung metastasis, but not primary tumor growth rate, in mice injected with tumors orthotopically. Furthermore, RKIP overexpression diminished vascular invasion in the primary tumors and tissue inhibitor of metalloproteinase-1 expression. These results identify RKIP as a clinically relevant novel prostate cancer MSG that suppresses metastasis, in part, through increasing vascular invasion that is associated with decreased TIMP-2 expression. Diminished expression of a signal transduction pathway inhibitor is a novel mechanism for promotion of metastasis.Ph.D.Biological SciencesCellular biologyHealth and Environmental SciencesMolecular biologyOncologyUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/123172/2/3068865.pd