8111

GPR68

G protein-coupled receptor 68;GPR68;G protein-coupled receptor 68

G-protein coupled receptor 68|ovarian cancer G protein-coupled receptor, 1|ovarian cancer G-protein coupled receptor 1|sphingosylphosphorylcholine receptor

14q31

protein-coding

Although bone pain in osteoporosis and skeletal metastasis is an expected consequence of fracture, there are other underlying causes responsible. Our study demonstrated that ovarian cancer G-protein-coupled receptor 1 detected extracellular protons in MG63 cells, and regulated osteoblast functions, such as prostaglandin E2 production, in response to acidic circumstances. In this work, we measured inositol phosphate production, intracellular Ca(2+) concentration, prostaglandin E2 production, and cyclic adenosine monophosphate accumulation in MG63 cells exposed to extracellular acidification. Extracellular acidity induced a transient increase in Ca(2+) concentration and inositol phosphate production. Acidification also induced prostaglandin E2 production, resulting in cyclic adenosine monophosphate accumulation. A small interfering RNA specific for the ovarian cancer G-protein-coupled receptor 1 markedly inhibited these proton-induced actions in MG63 cells. These results indicated that the involvement of ovarian cancer G-protein-coupled receptor 1 in acidic extracellular environment may be an underlying mechanism responsible for bone pain in osteoporosis or bone metastasis without clinically proved fractures.

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. CONCLUSION: 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.

Ovarian cancer G protein-coupled receptor 1 (OGR1) has been shown to be a proton sensing receptor in vitro. We have shown that OGR1 functions as a tumor metastasis suppressor gene when it is over-expressed in human prostate cancer cells in vivo. To examine the physiological functions of OGR1, we generated conditional OGR1 deficient mice by homologous recombination. OGR1 deficient mice were viable and upon gross-inspection appeared normal. Consistent with in vitro studies showing that OGR1 is involved in osteoclastogenesis, reduced osteoclasts were detected in OGR1 deficient mice. A pH-dependent osteoclasts survival effect was also observed. However, overall abnormality in the bones of these animals was not observed. In addition, melanoma cell tumorigenesis was significantly inhibited in OGR1 deficient mice. OGR1 deficient mice in the mixed background produced significantly less peritoneal macrophages when stimulated with thioglycolate. These macrophages also showed altered extracellular signal-regulated kinases (ERK) activation and nitric oxide (NO) production in response to lipopolysaccharide. OGR1-dependent pH responses assessed by cAMP production and cell survival in macrophages or brown fat cells were not observed, presumably due to the presence of other proton sensing receptors in these cells. Our results indicate that OGR1's role in osteoclastogenesis is not strong enough to affect overall bone development and its role in tumorigenesis warrants further investigation. The mice generated can be potentially used for several disease models, including cancers or osteoclast-related diseases.

Ovarian cancer G-protein-coupled-receptor-1 (OGR1) is a tumor metastasis suppressor in prostate cancer (PCa). OGR1 knockout mice (ogr1(-/-)) are grossly normal under physiological conditions, however, reduced melanoma tumorigenesis has been observed, with the mechanisms of this reduction completely unknown. In this work, we demonstrated that OGR1 deficiency in host cells significantly reduced tumorigenesis of PCa in mice. Adoptive transfer of WT CD11b(+) Gr1(+) double positive (DP) cells, but not T cells, was sufficient to allow tumor development in ogr1(-/-) mice. The expression of an M1 macrophage marker, inducible nitric oxide synthase (iNOS) was higher and expression of an M2 macrophage marker, arginase-1 (Arg 1) was lower in tumors from ogr1(-/-) mice compared with WT mice. Furthermore, coinjection of transgenic adenocarcinoma mouse prostate (TRAMP)-C2 cells with WT, but not ogr1(-/-) macrophages, increased tumor incidence in ogr1(-/-) mice. T-cell depletion experiments suggested that T cells were required for tumor rejection in ogr1(-/-)mice, although OGR1 expression in T cells may not be necessary. In summary, the expression of OGR1 in myeloid-derived cells, especially in DP cells, was required for PCa tumor cell-induced immunosuppression.