COEXPRESSION AND SECRETION OF C3, THE 3RD COMPONENT OF COMPLEMENT ANDA 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 an d involved in tumorigenicity and metastatic properties of these tumor cells. We demonstrate herein that DM-4 cells also secrete the p41 prot einase. Ln addition, analysis of cellular components which reacted wit h the p41 proteinase led us to demonstrate that DM-4 cells synthesized and secreted human C3. Secreted C3 is cleaved by the secreted p41 pro teinase and a C3dg-like fragment is generated. This is the first demon stration that a human melanoma cell line co-expresses and co-secretes human C3 and a C3-cleaving cysteine proteinase, antigenically related to procathepsin L. (C) 1997 Elsevier Science B.V.