Effects of Raf Kinase Inhibitor Protein Expression on Suppression of Prostate Cancer Metastasis

• Published in: JNCI : Journal of the National Cancer Institute Vol. 95; no. 12; pp. 878 - 889
• Main Authors: Fu, Zheng, Smith, Peter C., Zhang, Lizhi, Rubin, Mark A., Dunn, Rodney L., Yao, Zhi, Keller, Evan T.
• Format: Journal Article
• Language: English
• Published: Cary, NC Oxford University Press 18.06.2003; Oxford Publishing Limited (England)
• Subjects: Aged; Animals; Antineoplastic Agents - pharmacology; Antineoplastic Agents - therapeutic use; Biological and medical sciences; Blotting, Western; Effects; Enzyme Inhibitors - pharmacology; Enzyme Inhibitors - therapeutic use; Fluorescent Antibody Technique; Gene Expression Regulation, Enzymologic - drug effects; Gene Expression Regulation, Neoplastic - drug effects; Humans; Immunohistochemistry; Male; Medical sciences; Mice; Mice, SCID; Middle Aged; Neoplasm Invasiveness; Neovascularization, Pathologic - diagnosis; Nephrology. Urinary tract diseases; Prostate cancer; Prostate-Specific Antigen - analysis; Prostatic Neoplasms - drug therapy; Prostatic Neoplasms - enzymology; Prostatic Neoplasms - pathology; Proteins; Proto-Oncogene Proteins c-raf - antagonists & inhibitors; Proto-Oncogene Proteins c-raf - metabolism; Tumor Cells, Cultured; Tumor Stem Cell Assay; Tumors of the urinary system; Urinary tract. Prostate gland; Human; Urinary system disease; Prostate disease; Enzyme; Transferases; Enzyme inhibitor; Metastasis; Malignant tumor; In vitro; Kinase; Metastasis suppressor gene; Established cell line; Genetics; Male genital diseases; Prostate
• ISSN: 0027-8874; 1460-2105
• DOI: 10.1093/jnci/95.12.878

Background: Raf kinase inhibitor protein (RKIP), an inhibitor of Raf-mediated activation of mitogen-activated protein/extracellular signal-regulated kinase kinase (MEK), is expressed at lower levels in human C4-2B metastatic prostate cancer cells than in the parental non-metastatic LNCaP prostate cancer cells from which they were derived. We examined whether RKIP functions as a suppressor of metastasis. Methods: Immunohistochemistry was used to detect RKIP expression in clinical samples of primary prostate cancer and prostate cancer metastases. LNCaP and C4-2B cells were stably transfected with plasmids that constitutively expressed antisense and sense RKIP cDNA, respectively, or with empty vector. Assays of cell proliferation, soft-agar colony formation, and in vitro cell invasion were used to examine the malignant phenotypes of the transfected cells. An orthotopic murine model was used to examine the effect of expressing RKIP in C4-2B cells on the development of spontaneous metastasis. Results: Clinical samples of primary prostate cancer had detectable RKIP expression, whereas clinical samples of prostate cancer metastases did not. There were no differences in the in vitro proliferation rate or colony-forming ability between the control vector-transfected and sense RKIP vector-transfected C4-2B cells or between the control vector-transfected and the antisense RKIP vector-transfected LNCaP cells. Overexpression of RKIP in C4-2B cells was associated with decreased in vitro cell invasion, decreased development of lung metastases in vivo, and decreased vascular invasion in the primary tumor but did not affect primary tumor growth in mice. Conclusions: RKIP does not influence the tumorigenic properties of human prostate cancer cells. It appears to be a novel and clinically relevant suppressor of metastasis that may function by decreasing vascular invasion.