Ovarian cancer G protein-coupled receptor 1, a new metastasis suppressor gene in prostate cancer.
BACKGROUND
Metastasis is a process by which tumors spread from primary organs to other sites in the body and is the major cause of death for cancer patients. The ovarian cancer G protein-coupled receptor 1 (OGR1) gene has been shown to be expressed at lower levels in metastatic compared with primary prostate cancer tissues.


METHODS
We used an orthotopic mouse metastasis model, in which we injected PC3 metastatic human prostate cancer cells stably transfected with empty vector (vector-PC3) or OGR1-expressing vector (OGR1-PC3) into the prostate lobes of athymic or NOD/SCID mice (n = 3-8 mice per group). Migration of PC3 cells transiently transfected with vector control or with OGR1- or GPR4 (a G protein-coupled receptor with the highest homology to OGR1)-expressing vectors was measured in vitro by Boyden chamber assays. G protein alpha-inhibitory subunit 1 (G alpha(i1)) expression after treatment with pertussis toxin (PTX) was measured using immunoblotting analysis. The inhibitory factor present in the conditioned medium was extracted using organic solvents and analyzed by mass spectrometry.


RESULTS
In vivo, all 26 mice carrying tumors that were derived from vector-PC3 cells developed prostate cancer metastases (mean = 100%, 95% confidence interval [CI] = 83.97% to 100%) but few (4 of 32) mice carrying tumors derived from OGR1-expressing PC3 cells (mean = 12.50%, 95% CI = 4.08% to 29.93%) developed metastases. However, exogenous OGR1 overexpression had no effect on primary prostate tumor growth in vivo. In vitro, expression of OGR1, but not GPR4, inhibited cell migration (mean percentage of cells migrated, 30.2% versus 100%, difference = 69.8%, 95% CI = 63.0% to 75.9%; P<.001) via increased expression of G alpha(i1) and the secretion of a chloroform/methanol-extractable heat-insensitive factor into the conditioned medium through a PTX-sensitive pathway.


CONCLUSIONS
OGR1 is a novel metastasis suppressor gene for prostate cancer. OGR1's constitutive activity via G alpha(i) contributes to its inhibitory effect on cell migration in vitro.
Singh
Lisam Shanjukumar
LS
Department of Obstetrics and Gynecology, Indiana University School of Medicine, 975 W. Walnut St, Indianapolis, IN 46202, USA.
Berk
Michael
M
Oates
Rhonda
R
Zhao
Zhenwen
Z
Tan
Haiyan
H
Jiang
Ying
Y
Zhou
Aimin
A
Kirmani
Kashif
K
Steinmetz
Rosemary
R
Lindner
Daniel
D
Xu
Yan
Y
D000818:Animals; D045744:Cell Line, Tumor; D002465:Cell Movement / Q000235:genetics; D017931:DNA Primers; D016147:Genes, Tumor Suppressor; D006801:Humans; D008297:Male; D051379:Mice; D008819:Mice, Nude; D009362:Neoplasm Metastasis / Q000235:genetics* / Q000517:prevention & control; D010957:Plasmids; D016133:Polymerase Chain Reaction; D011471:Prostatic Neoplasms / Q000235:genetics* / Q000517:prevention & control; D043562:Receptors, G-Protein-Coupled / Q000235:genetics*; D014162:Transfection; D014183:Transplantation, Heterologous
D017931:DNA Primers; C486281:GPR68 protein, human; D043562:Receptors, G-Protein-Coupled