RESUMO
Membrane type 1 matrix metalloproteinase (MT1-MMP) plays an essential role in protease-mediated extracellular matrix (ECM) degradation, but it also functions as a sheddase releasing non-ECM substrates such as receptor activator of NF-kappaB ligand (RANKL), an osteoclastogenic factor typically confined to the surface of osteoblasts. We previously found high expression of MT1-MMP in skeletal metastasis of prostate cancer patients, in a pattern similar to RANKL expression. We also showed that overexpression of MT1-MMP in prostate cancer cells increases tumor growth and osteolysis in an intratibial mouse model of bone metastasis, and that soluble factor(s) shed by tumor-derived MT1-MMP enhance osteoclast differentiation in a RANKL-dependent manner. Recent evidence indicates that the cognate receptor for RANKL, RANK, is expressed in prostate cancer cells, suggesting the presence of an autocrine pathway. In this study, we show that MT1-MMP-expressing LNCaP prostate cancer cells display enhanced migration. Moreover, conditioned medium from LNCaP cells expressing both RANKL and MT1-MMP stimulates the migration of MT1-MMP-deficient C42b prostate cancer cells. This enhanced chemotaxis can be abrogated by osteoprotegerin (soluble decoy receptor of RANKL), MIK-G2 (a selective inhibitor for MT1-MMP), and PP2 (a Src inhibitor). These findings indicate that tumor-derived MT1-MMP enhances tumor cell migration through initiation of an autocrine loop requiring ectodomain shedding of membrane-bound RANKL in prostate cancer cells, and that Src is a key downstream mediator of RANKL-induced migration of prostate cancer cells.
Assuntos
Movimento Celular/fisiologia , Metaloproteinase 14 da Matriz/metabolismo , Neoplasias da Próstata/patologia , Ligante RANK/metabolismo , Quinases da Família src/metabolismo , Animais , Neoplasias Ósseas/secundário , Linhagem Celular Tumoral , Ativação Enzimática , Humanos , Masculino , Metaloproteinase 14 da Matriz/biossíntese , Metaloproteinase 14 da Matriz/genética , Camundongos , Neoplasias da Próstata/genética , Neoplasias da Próstata/metabolismo , TransfecçãoRESUMO
A variety of proteases have been implicated in prostate cancer (PC) bone metastasis, but the individual contributions of these enzymes remain unclear. Urokinase-type plasminogen activator (uPA), a serine protease, can activate plasminogen and stimulate signaling events on binding its receptor uPAR. In the present study, we investigated the functional role of PC cell-associated uPA in intraosseous tumor growth and bone matrix degradation. Using a severe combined immunodeficient-human mouse model, we found that PC3 cells were the major source of uPA in the experimental bone tumor. Injection of uPA-silenced PC3 cells in bone xenografts resulted in significant reduction of bone tumor burdens and protection of trabecular bones from destruction. The suppressed tumor growth was associated with the level of uPA expression but not with its activity. An increase in the expression of PAI-1, the endogenous uPA inhibitor, was found during in vitro tumor-stromal interactions. Up-regulation of PAI-1 in bone stromal cells and preosteoclasts/osteoblasts was due to soluble factor(s) released by PC cells, and the enhanced PAI-1 expression in turn stimulated PC cell migration. Our results indicate that both tumor-derived uPA and tumor-stroma-induced PAI-1 play important roles in intraosseous metastatic PC growth through regulation of a uPA-uPAR-PAI-1 axis by autocrine/paracrine mechanisms.