Effects of raf kinase inhibitor protein expression on suppression of prostate cancer metastasis.
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.
Fu
Zheng
Z
Program in Immunology, School of Medicine, University of Michigan, Ann Arbor 48109-0940, USA.
Smith
Peter C
PC
Zhang
Lizhi
L
Rubin
Mark A
MA
Dunn
Rodney L
RL
Yao
Zhi
Z
Keller
Evan T
ET
D000368:Aged; D000818:Animals; D000970:Antineoplastic Agents / Q000494:pharmacology* / Q000627:therapeutic use; D015153:Blotting, Western; D004791:Enzyme Inhibitors / Q000494:pharmacology* / Q000627:therapeutic use; D005455:Fluorescent Antibody Technique; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D006801:Humans; D007150:Immunohistochemistry; D008297:Male; D051379:Mice; D016513:Mice, SCID; D008875:Middle Aged; D009361:Neoplasm Invasiveness; D009389:Neovascularization, Pathologic / Q000175:diagnosis; D017430:Prostate-Specific Antigen / Q000032:analysis; D011471:Prostatic Neoplasms / Q000188:drug therapy* / Q000201:enzymology / Q000473:pathology*; D019908:Proto-Oncogene Proteins c-raf / Q000037:antagonists & inhibitors* / Q000378:metabolism; D014407:Tumor Cells, Cultured; D014410:Tumor Stem Cell Assay
D000970:Antineoplastic Agents; D004791:Enzyme Inhibitors; D019908:Proto-Oncogene Proteins c-raf; D017430:Prostate-Specific Antigen