Co-expression and secretion of C3, the third component of complement and a C3-cleaving cysteine proteinase in a highly metastatic human melanoma cell line.

We recently demonstrated that DM-4, a human melanoma cell line highly metastatic in nude mice, expressed a p41 C3-cleaving proteinase. This p41 proteinase is a cysteine proteinase, associated to cell surface and involved in tumorigenicity and metastatic properties of these tumor cells. We demonstrate herein that DM-4 cells also secrete the p41 proteinase. In addition, analysis of cellular components which reacted with the p41 proteinase led us to demonstrate that DM-4 cells synthesized and secreted human C3. Secreted C3 is cleaved by the secreted p41 proteinase and a C3dg-like fragment is generated. This is the first demonstration that a human melanoma cell line co-expresses and co-secretes human C3 and a C3-cleaving cysteine proteinase, antigenically related to procathepsin L.