Tissue inhibitor of matrix metalloproteinase-2 regulates matrix metalloproteinase-2 activation by modulation of membrane-type 1 matrix metalloproteinase activity in high and low invasive melanoma cell lines

Activation of pro-matrix metalloproteinase (MMP)-2 on the surface of malign ant cells by membrane-bound MT1-MMP is believed to play a critical role dur ing tumor progression and metastasis. In this study we present evidence tha t MT1-MMP plays a key role for the in vitro invasiveness of malignant melan oma. Melanoma cell lines secreted latent MMP-2 when cultured on plastic. Ho wever, when cells were grown in floating type I collagen lattices, only hig h invasive melanoma cells activated proMMP-2. Activation could be inhibited by antibodies against MT1-MMP, by addition of recombinant tissue inhibitor of metalloproteinases (TIMP)-2 and by inhibition of MT1-MMP cleavage. MT1- MMP protein was detected as an inactive protein in all cell lines cultured as monolayers, whereas in collagen gels, active MT1-MMP protein was detecte d in the membranes of both high and low invasive melanoma cells. Production of TIMP-2 was about 10-fold higher in low invasive cells as compared with high invasive melanoma cells and was further increased in the low invasive cells upon contact to collagen. Thus, in melanoma cells TIMP-2 expression l evels might regulate MT1-MMP-mediated activation of proMMP-2. High invasive melanoma cells displayed increased in vitro invasiveness, which was inhibi ted by TIMP-8. These data indicate the importance of these enzymes for the invasion processes and support a role for MT1-MMP as an activator of proMMP -2 in malignant melanoma.