Cytotoxic sensitivity to tumor necrosis factor-alpha in PC3 and LNCaP prostatic cancer cells is regulated by extracellular levels of SGP-2 (clusterin)

BACKGROUND. SGP-2 is a ubiquitous secreted glycoprotein that prevents cellu lar apoptosis. This study was carried out to determine the extracellular ac tion of SGP-2 in a model of tumor necrosis factor-alpha (TNF)-induced cytot oxicity using two human prostatic cancer lines, LNCaP and PC3. These two li nes were selected because LNCaP cells are highly sensitive to the cytotoxic effect of TNF, while PC3 cells are resistant to TNF at 24 hr. METHODS. Cells were cultured in the presence or absence of TNF (10 ng/ml). LNCaP cells were treated with varying concentrations of exogenous SGP-2, wh ile PC3 cells were treated with antisera to SGP-2 with and without exogenou s SGP-2. Following a 24-hr treatment, cultures were assessed by counting of cell number and by the trypan blue exclusion assay. RESULTS. Western blot analysis of conditioned media revealed that PC3 secre ted more SGP-2 than did LNCaP. The sensitivity to TNF in LNCaP cells was re duced by the addition of exogenous SGP-2. PC3 cells became sensitive to TNF when SGP-2 antibody was added to the culture. The effect of SGP-2 antibody on PC3 cells was reversed by the addition of exogenous SGP-2 to the cultur e. CONCLUSIONS. These results suggest that SGP-2 can act as an extracellular m ediator of anti-TNF-induced cytotoxicity. (C) 1999 Wiley-Liss, Inc.