The ability to invade host tissues and form distant metastases is a primary distinguishing characteristic of malignant cells as well as the major cause of cancer fatality. Tumor invasion is facilitated by proteolytic degradation of the extracellular matrix (ECM) mediated primarily by plasminogen activators and matrix metalloproteinases. Our long-term goal is to elucidate the molecular mechanisms involved in regulation of tumor cell-associated ECM proteolysis. Our working hypothesis is that tumor cell-mediated basement membrane proteolysis releases fragments of ECM proteins which stimulate proteinase secretion and/or activity and thereby facilitate metastasis. In this study, matrix regulation of the proteinase secretion profiles of metastatic tumor cells and of the biological activity of the secreted proteinases will be determined using in vitro biochemical studies, tumor cells in culture, and an in vivo animal metastasis model. Initially, the effects of specific isolated domains of the ECM proteins type IV collagen (CIV), laminin (LN) and fibronectin (FN) on the biochemical properties of purified tissue plasminogen activator (t-PA) and matrix metalloproteinase-2 (MMP-2, type IV collagenase) will be determined using ligand blotting and kinetic studies. The effect of ECM fragments on the synthesis, secretion and subsequent biological activity of t-PA, MMP-2 and their respective specific proteinase inhibitors will be determined using cultured melanoma cells. Comparison will be made between the proteinase and inhibitor profiles of a highly metastatic melanoma cell line and a parental melanoma line with low metastatic activity. Lastly, the murine melanoma lung colonization model will be used to identify specific ECM fragments, characterized in previous studies, which potentiate or inhibit experimental metastasis in vivo. Together, these studies will increase our understanding of the molecular mechanisms by which fragments of ECM proteins regulate tumor invasion and metastasis.
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