C3-cleaving membrane proteinase. A new complement regulatory protein of human melanoma cells.
Human melanoma cells resistant to killing by the R24 mAb and human complement rapidly degrade surface-deposited C3b (M. Panneerselvam, S. Welt, L. J. Old, C.-W. Vogel. 1986. J. Immunol. 136:2534). We report that C-resistant melanoma cells express a membrane proteinase that can cleave C3b, generating a cleavage product with a molecular mass of approximately 30 kDa. The C3-cleaving proteinase was identified on the melanoma cells by its cross-reaction with antiserum to p57, a C3-cleaving proteinase previously isolated from human E membranes (C. Charriaut-Marlangue, M. Barel, R. Frade. 1986. Biochem. Biophys. Res. Commun. 140:1113). Preincubation of the C-resistant melanoma cells with anti-p57 IgG or their F(ab')2 fragments increased their susceptibility to complement killing from 25% to approximately 50% and reduced the rate of C3b cleavage and the amount of the 30-kDa fragment generated on the cells. Anti-p57 IgG stained C-resistant melanoma cells by indirect immunofluorescence and precipitated a protein with an apparent molecular mass of 65 kDa. This membrane protein, termed p65, was not detectable on C-susceptible melanoma cells. Membrane extracts from C-resistant melanoma cells also showed C3-cleaving activity when incubated with purified C3 or C3b, similarly generating a C3 fragment of approximately 35 kDa. This fluid-phase C3 cleaving activity could be partially inhibited by anti-p57 IgG. These data suggest that p65 is a C3-cleaving proteinase, antigenically related to p57, that is expressed on C-resistant melanoma cells and responsible for the C resistance of these cells. We propose that the membrane-bound C3-cleaving proteinase represents another C regulatory protein protecting host cells against killing by C.
Department of Biochemistry, Georgetown University School of Medicine, Washington, DC 20007.
M W
MW
Ollert
R
R
Frade
A
A
Fiandino
M
M
Panneerselvam
E C
EC
Petrella
M
M
Barel
M K
MK
Pangburn
R
R
Bredehorst
C W
CW
Vogel
D015153:Blotting, Western; D002462:Cell Membrane / Q000201:enzymology; D003167:Complement Activation; D003176:Complement C3 / Q000378:metabolism*; D005455:Fluorescent Antibody Technique; D006801:Humans; D007158:Immunologic Techniques; D008545:Melanoma / Q000201:enzymology / Q000276:immunology*; D008970:Molecular Weight; D010447:Peptide Hydrolases / Q000378:metabolism*; D011233:Precipitin Tests; D013997:Time Factors
D003176:Complement C3; D010447:Peptide Hydrolases