RANK is a transmembrane signaling receptor of the tumor necrosis factor (TNF) receptor superfamily that is expressed on the surface of osteoclast precursors [61] and [62]. Its cognate ligand, RANKL, is expressed almost exclusively within the bone marrow stromal cell compartment and is up-regulated by most hormones and factors that stimulate bone resorption [7] and [60]. The interaction of RANK and RANKL is necessary for osteoclast formation, function,

and survival [58] and [63]. RANKL (50 ng/ml) stimulates osteoclastogenesis in mouse total bone marrow cells in the presence of 100 ng/ml CCN2 (Fig. 2D) [33]. Stromal/osteoblastic cells are essential for in vitro osteoclastogenesis through cell-to-cell interactions [64]. Therefore, it

has been hypothesized that CCN2 may facilitate GW3965 cell-to-cell signaling by interacting with multiple molecules on the surface of these cells through integrin [19] and [65], proteoglycans [66], and growth factors [18]. Tumor-produced endothelin-1 (ET-1) is also a key mediator of osteoblastic bone metastasis, which is characteristic of breast and prostate cancers see more [67] and [68]. CCN2 is one of the secreted factors downstream of ET-1, as determined from microarray analysis of osteoblasts [69]. ET-1 activates the CCN2 promoter and induces CCN2 expression in cardiomyocyte cells [70]. Furthermore, ET-1 induces CCN2 in an additive fashion to TGF-β through an element distinct

from the TGF-β response element [71], [72] and [73]. In the bone Cediranib (AZD2171) marrow microenvironment affected by tumor, substantial bone marrow angiogenesis is present compared with healthy persons [74]. In the case of the best-characterized CCN2, this factor is known to promote the proliferation and differentiation of vascular endothelial cells as well as fibroblasts and osteoblasts [22], [24], [25] and [75]. CCN2 protein is able to interact with multiple molecules in the bone microenvironment, thus resulting in the modulation of the extra cellular molecular network therein. The angiogenic effects of CCN2 is the results of the interaction with adhesion molecules [19], cell-surface signal transducing receptors [76], proteoglycans [66] and growth factors [18]. Bone-derived growth factors, such as TGF-β, FGFs, PDGFs, BMPs, and IGF-1 are activated and released into the bone microenvironment. Elevated TGF-β does not appear to affect tumor growth, but rather leads to the production of PTHrP [77] and CCN2 [39] and [45] in breast cancer cells, thus establishing a continuously destructive cycle termed the “vicious cycle” through up-regulation of RANKL and accelerated bone resorption. Of note, CCN2 is known to interact with these growth factors [16] and [18] or regulate the gene expression of some of them [37].