CXCR7: a novel tumor endothelial marker in renal cell carcinoma.

Tumor angiogenesis is necessary for progression and metastasis of solid tumor. Tumor blood vessels are morphologically different from their normal counterparts. In this study, we isolated tumor endothelial cells (TECs) and revealed their abnormalities. We have compared the gene expression profiles of TECs and normal endothelial cells (NECs) by microarray analysis and found that several genes were upregulated in TECs. Expression of the chemokine receptor CXCR7 mRNA was higher in TECs than in NECs. However, information regarding the expression of CXCR7 in the tumor vessels of renal cell carcinoma is limited. CXCR7 and its ligand CXCL12 have been implicated in tumor cell survival. In this study, the expression of CXCR7 in the tumor vessels of renal cell carcinoma (RCC) was investigated. Real-time PCR revealed higher expression level of CXCR7 in cultured TECs than in cultured NECs. Furthermore, similar to mouse TECs, immunostaining revealed strong expression of CXCR7 in vivo in human tumor vessels. These findings suggest that CXCR7 is a novel TEC marker and a target for antiangiogenic therapy for RCC.

Prostacyclin receptor in tumor endothelial cells promotes angiogenesis in an autocrine manner.

Molecules highly expressed in tumor endothelial cells (TEC) are important for specific targeting of these cells. Previously, using DNA microarray analysis, we found that the prostacyclin receptor (IP receptor) gene was upregulated in TEC compared with normal endothelial cells (NEC). Although prostacyclin is implicated in re-endothelialization and angiogenesis, its role remains largely unknown in TEC. Moreover, the effect of the IP receptor on TEC has not been reported. In the present study we investigated the function of the IP receptor in TEC. The TEC were isolated from two types of human tumor xenografts in nude mice, while NEC were isolated from normal counterparts. Prostacyclin secretion levels in TEC were significantly higher than those in NEC, as shown using ELISA. Real-time RT-PCR showed that the IP receptor was upregulated in TEC compared with NEC. Furthermore, migration and tube formation of TEC were suppressed by the IP receptor antagonist RO1138452. Immunohistostaining showed that the IP receptor was specifically expressed in blood vessels of renal cell carcinoma specimens, but not in glomerular vessels of normal renal tissue. These findings suggest that the IP receptor is a TEC-specific marker and might be a useful therapeutic target.

Activation of the FGF signaling pathway and subsequent induction of mesenchymal stem cell differentiation by inorganic polyphosphate.

Inorganic polyphosphate [poly(P)] is a biopolymer existing in almost all cells and tissues, although its biological functions in higher eukaryotes have not been completely elucidated. We previously demonstrated that poly(P) enhances the function of fibroblast growth factors (FGFs) by stabilizing them and strengthening the affinity between FGFs and their cell surface receptors. Since FGFs play crucial roles in bone regeneration, we further investigated the effect of poly(P) on the cell differentiation of human stem cells via FGF signaling systems. Human dental pulp cells (HDPCs) isolated from human dental pulp show the characteristics of multipotent mesenchymal stem cells (MSCs). HDPCs secreted FGFs and the proliferation of HDPCs was shown to be enhanced by treatment with poly(P). Cell surface receptor-bound FGF-2 was stably maintained for more than 40 hours in the presence of poly(P). The phosphorylation of ERK1/2 was also enhanced by poly(P). The effect of poly(P) on the osteogenic differentiation of HDPCs and human MSCs (hMSCs) were also investigated. After 5 days of treatment with poly(P), type-I collagen expression of both cell types was enhanced. The C-terminal peptide of type-I collagen was also released at higher levels in poly(P)-treated HDPCs. Microarray analysis showed that expression of matrix metalloproteinase-1 (MMP1), osteopontin (OPN), osteocalcin (OC) and osteoprotegerin was induced in both cell types by poly(P). Furthermore, induced expression of MMP1, OPN and OC genes in both cells was confirmed by real-time PCR. Calcification of both cell types was clearly observed by alizarin red staining following treatment with poly(P). The results suggest that the activation of the FGF signaling pathway by poly(P) induces both proliferation and mineralization of stem cells.

Modulation of mitogenic activity of fibroblast growth factors by inorganic polyphosphate.

The proliferation of normal human fibroblast cells was enhanced by the addition of inorganic polyphosphate (poly(P)) into culture media. The mitogenic activities of acidic fibroblast growth factor (FGF-1) and basic fibroblast growth factor (FGF-2) were also enhanced by poly(P). A physical interaction between poly(P) and FGF-2 was observed, and FGF-2 was both physically and functionally stabilized by poly(P). Furthermore, poly(P) facilitated the FGF-2 binding to its cell surface receptors. Because poly(P) is widely distributed in mammalian tissues, it may be a spontaneous modulator of FGFs.