ADAMTS1 and MMP1 proteolytically engage EGF-like ligands in an osteolytic signaling cascade for bone metastasis

Abstract

Bone metastasis is mediated by complex interactions between tumor cells and resident stromal cells in the bone microenvironment. The functions of metalloproteinases in organ-specific metastasis remain poorly defined despite their well-appreciated role in matrix degradation and tumor invasion. Here, we show a mechanism whereby two distinct metalloproteinases, a disintegrin and metalloproteinase with thrombospondin motifs (ADAMTS1) and matrix metalloproteinase-1 (MMP1), orchestrate a paracrine signaling cascade to modulate the bone microenvironment in favor of osteoclastogenesis and bone metastasis. Proteolytic release of membranebound epidermal growth factor (EGF)-like growth factors, including Amphiregulin (AREG), heparin-binding EGF (HB-EGF), and transforming growth factor a (TGFa) from tumor cells suppress the expression of osteoprotegerin (OPG) in osteoblasts and subsequently potentiate osteoclast differentiation. EGF receptor (EGFR) inhibitors block osteolytic bone metastasis by targeting EGFR signaling in bone stromal cells. Furthermore, elevated MMP1 and ADAMTS1 expression is associated with increased risk of bone metastasis in breast cancer patients. This study established MMP1 and ADAMTS1 in tumor cells, as well as EGFR signaling in osteoblasts, as promising therapeutic targets for inhibiting bone metastasis of breast cancer. Increased osteoclast activity leads to bone matrix degradation and the release of bone-derived growth factors that can further stimulate the metastatic function of tumor cells. Central to the control of this so-called ''vicious cycle'' of bone metastasis is the modulation of osteoclast activity by the tumor necrosis factor (TNF) family member receptor activator of nuclear kB ligand (RANKL) (Mundy 2002). RANKL is expressed in both membranebound and soluble forms by osteoblasts, while its cognate receptor RANK is expressed on the surface of osteoclasts and controls a key signaling pathway essential for osteoclast differentiation. Osteoprotegerin (OPG), a soluble decoy receptor of RANKL, is also produced by osteoblasts to antagonize the activity of RANKL. The function of tumor-derived bone metastasis factors, such as parathyroid hormone-related peptide (PTHrP), hinges upon their ability to increase RANKL production or decrease OPG secretion by osteoblasts, ultimately promoting osteoclast differentiation and activation (Mundy 2002).

Epidermal growth factor signalling and bone metastasis

“…It is conceivable that by interacting with osteoblasts through paracrine EGF signalling, the tumour cells can ultimately promote osteoclastogenesis. Indeed, this possibility was confirmed in our recent study (Lu et al, 2009). …”

“…The former leads to severe heart failure and enlarged heart valves (similar to the phenotypes in HB-EGF-null and EGFR-null animals), whereas the latter causes hyperplasia in the skin and heart. Our recent study highlights the importance of ectodomain shedding of HB-EGF, AREG and TGF-a by proteases MMP1 and ADAMTS1 in the establishment of paracrine signalling cascade in bone metastasis (discussed below) (Lu et al, 2009). Besides the G-protein-coupled receptors, other signals can also activate protease-mediated ectodomain shedding, such as Wnt/Frizzled and oestradiol/oestrogen receptor (Hynes and Lane, 2005).…”

“…Next, we will introduce the molecular mechanisms governing bone homoeostasis and bone metastasis. Finally, we will discuss several recent findings that established a role for EGF signalling in the complex network of tumour -stromal cross talks during the formation of osteolytic bone metastasis Weber et al, 2003;Normanno et al, 2005;Lu et al, 2009). These studies provide the foundation for evaluating ERBBs and their ligands as potential therapeutic targets for controlling bone metastasis.…”

“…By doing this, EGF signalling can indirectly influence osteoclast number and activity. The indirect role of EGF signalling in osteoclastogenesis was explored using either the mesenchymal stem cell-like cells (Normanno et al, 2005) or osteoblast cell lines (Zhu et al, 2007;Lu et al, 2009), and the results suggest that activation of the signalling pathway upregulates RANKL, macrophage colony stimulating factor and MCP-1, but downregulates OPG (Figure 1). The overall consequence of these regulations is enhanced osteoclast differentiation.…”

The ADAMTS1 Protease Gene Is Required for Mammary Tumor Growth and Metastasis

“…A similar mechanism was demonstrated by overexpression of both MMP1 and ADAMTS1 proteases in weakly metastatic MDA-MB231 breast cancer sublines, resulting in augmented paracrine release of EGF-like ligands and enhanced bone metastasis. 46 In PyMT ϩ mammary tumors, the apoptotic index was lower in Adamts1 ϩ/ϩ than in Adamts1 Ϫ/Ϫ tumors, despite equivalent vascular density and cleaved versican accumulated in peritumoral stroma. The liberated G3 domain of cleaved versican has EGF-like activity [47][48][49] and might act as an EGF-like signal in the Adamts1 ϩ/ϩ tumor microenvironment, resulting in reduced apoptosis and increased tumor growth compared with null littermates.…”