The p75NTR metastasis suppressor inhibits urokinase plasminogen activator, matrix metalloproteinase-2 and matrix metalloproteinase-9 in PC-3 prostate cancer cells

The p75 neurotrophin receptor (p75NTR) has been characterized as a metastasis and tumor suppressor in prostate cancer. In order to investigate the mechanism(s) by which the p75NTR functions as a metastasis suppressor in prostate cancer cells, we characterized the ectopic expression of p75NTR on the urokinase plasminogen activator (uPA) and the type IV collagen matrix metalloproteinases (MMP-2 and MMP-9) in PC-3 human prostate cancer cells. Rank-order expression of p75NTR greatly reduced protein levels and enzymatic activities of uPA, MMP-2, and MMP-9 as shown by immunoblot and zymography analyses. Conversely, expression of the MMP-9 antagonist, tissue inhibitor of matrix metalloproteinase-1 (TIMP-1) exhibited an increase in protein levels with an increase in p75NTR levels, whereas TIMP-2 was not detected. Transient transfection with an inducible dominant negative antagonist Δp75NTR rescued uPA, MMP-2, and MMP-9 protein levels and protease activities, and conversely suppressed TIMP-1 levels. Since p75NTR signal transduction occurs via the NFκB and JNK pathways, antagonism of signaling intermediates in these pathways, using dominant negative IKKβ or dominant negative MKK-4, respectively, was shown to further decrease expression of uPA, MMP-2, and MMP-9 protein and enzymatic activity levels, and conversely up-regulate levels of TIMP-1. These results indicate that expression of uPA, MMP-2, MMP-9, and TIMP-1 are directly regulated by expression of p75NTR and its downstream signal transduction cascade. These results suggest that the metastasis suppressor activity of p75NTR is mediated, in part, by down-regulation of specific proteases (uPA, type IV collagenases) implicated in cell migration and metastasis.