endothelin-1 and Sarcoma--Kaposi

Endothelin-1 (ET-1) and its receptors are overexpressed in human Kaposi's sarcoma lesions. Here we show that in human KS IMM cell line ET-1 increased secretion and activation of matrix-metalloproteinase-2 (MMP-2), -3, -7, -9 and -13, as well as of membrane-type 1-MMP (MT1-MMP). ET-1 and ET-3 also enhanced the expression of tissue inhibitor of MMP-2, essential for MT1-MMP-mediated MMP-2 activation. Combined addition of both ET(B) receptor (ET(B)R) and ET(A)R antagonists completely blocked the ET-1-induced MMP activity. By immunohistochemistry, we observed that ET-1 increased MMP-2 and MT1-MMP expression and their localization at the cell surface. Treatment with both antagonists resulted also in the suppression of ET-1-induced phosphorylation of focal adhesion proteins, FAK and paxillin, which are essentials for cell motility. ET-1 induced a dose-dependent enhancement in KS IMM cell migration and MMP-dependent invasiveness that were inhibited by ET-1 receptor antagonists. The small molecule, A-182086, an orally bioavailable ET(A/B)R antagonist, completely inhibited cell proliferation and tumor growth in KS IMM xenografts. These findings demonstrate that ET-1-driven autocrine loop is crucial for enhanced invasiveness of KS IMM cells and promote tumor growth in vivo. Such activities can be blocked by the ET(A/B)R antagonists, which may be effective anti-angiogenic and anti-tumor molecules for the treatment of Kaposi's sarcoma.

Topics: Animals; Cell Division; Cell Movement; Cell Transplantation; Culture Media, Conditioned; Cytoskeletal Proteins; Endothelin Receptor Antagonists; Endothelin-1; Endothelin-3; Enzyme Activation; Female; Focal Adhesion Kinase 1; Focal Adhesion Protein-Tyrosine Kinases; Humans; Matrix Metalloproteinases; Mice; Mice, Nude; Paxillin; Phosphoproteins; Protein-Tyrosine Kinases; Receptor, Endothelin A; Receptor, Endothelin B; Receptors, Endothelin; Sarcoma, Kaposi; Tissue Inhibitor of Metalloproteinase-2; Tumor Cells, Cultured

Endothelin-1 (ET-1) has been shown to be mitogenic for endothelial and several tumor cells through an autocrine mechanism. In this study we evaluated whether the tumorigenic KS IMM cell line deriving from Kaposi's sarcoma (KS), a highly angiogenic tumor, is susceptible to ET-1 mitogenic activity. By reverse transcriptase-polymerase chain reaction, we detected ET-1 mRNA expression and both ET(A) receptor (ET(A)R) and ET(B)R mRNA transcripts in the KS IMM cells. High concentrations of ET-1 are released from the KS IMM cells and competition-binding studies demonstrated that these cells also express functional ET(A)R and ET(B)R with high affinity for ET-1 and ET-1/ET-3, respectively. Expression of ET-1 and cognate receptors could be detected by immunohistochemical method in vitro, in KS IMM xenograft, and in tissue sections of a human KS lesion. Furthermore ET-1 induces a marked and dose-dependent increase in [3H]thymidine incorporation comparable to that elicited by vascular endothelial growth factor. Addition of both selective ET(B)R antagonist (BQ 788) and ET(A)R antagonist (BQ 123), completely blocked ET-1-induced mitogenic response and reduced the basal growth rate of unstimulated cells, suggesting that both receptors mediated the proliferative signal. Such findings demonstrate that ET-1 participates on KS pathogenesis acting as an autocrine growth factor and that ET-1 receptor antagonists may thus be novel candidates for therapeutic intervention.

Topics: Animals; Autocrine Communication; Cell Division; Cells, Cultured; Endothelin Receptor Antagonists; Endothelin-1; Humans; Mice; Mice, Nude; Oligopeptides; Peptides, Cyclic; Piperidines; Protein Isoforms; Receptors, Endothelin; Sarcoma, Kaposi; Transcription, Genetic; Tumor Cells, Cultured