J. Hakulinen et S. Meri, EXPRESSION AND FUNCTION OF THE COMPLEMENT MEMBRANE ATTACK COMPLEX INHIBITOR PROTECTIN (CD59) ON HUMAN BREAST-CANCER CELLS, Laboratory investigation, 71(6), 1994, pp. 820-827
BACKGROUND: Normal human cells resist the lytic activity of homologous
complement (C) by expressing inhibitory molecules on their cell membr
anes. Recently, it has become increasingly evident that information on
C inhibitors on malignant tumor cells is crucial before considering a
ny immunotherapeutic attempts with C-activating antibodies. As one of
the most potent inhibitors of C lysis is protectin (CD59), we have exa
mined its expression and function on human breast cancer cells. EXPERI
MENTAL DESIGN: Immunofluorescence microscopy was used to detect protec
tin expression on solid breast tumor samples (N = 12). Using immunoaff
inity chromatography, protectin was isolated from the membranes of cul
tured MCF7 and T47D breast cancer cells. The purified proteins were in
corporated into heterologous cells to study their C inhibitory activit
ies. The reactivity of tumor cell protectins with terminal C complexes
was examined by sucrose density ultracentrifugation analysis. A chrom
ium release assay was used to study the effects of protectin neutraliz
ation on the sensitivity of MCF7 and T47D cells to C-mediated cytotoxi
city. RESULTS: Protectin was found to be strongly expressed by all hum
an breast cancer tumors examined. The affinity-purified protectins had
a glycophosphoinositollipid anchor and migrated in sodium dodecyl sul
fate-polyacrylamide gel electrophoresis as glycosylated smears of 19 t
o 25 kilodaltons. Protectin isolated from T47D cells bound to nascent
C5b-9 complexes generated in human sera and inhibited C lysis of guine
a pig erythrocytes when incorporated into their cell membranes. C-medi
ated killing of breast cancer cells could be significantly enhanced af
ter treatment of the cells with F(ab')(2) fragments of the anti-protec
tin monoclonal antibody YTH53.1. CONCLUSIONS: Human breast cancer cell
s resist C membrane attack by expressing protectin on their cell membr
anes. Neutralization of protectin on the surface of the tumor cells in
creases their sensitivity to C lysis.