Bovine seminal ribonuclease induces in vitro concentration dependent apoptosis in stimulated human lymphocytes and cells from human tumor cell lines

Bovine seminal ribonuclease (BS RNase), a dimeric homolog of bovine pancrea tic ribonuclease has been proven to have important biological properties as aspermatogenic, antitumor, embryotoxic and immunosuppressive activities. R ecently we published preliminary results concerning the ability of bovine s eminal ribonuclease (BS RNase) to induce time dependent apoptosis in Con-A stimulated human lymphocytes and in human tumor cells based on DNA content and cell cycle analysis. Tn this study we bring more confirmative data conc erning the concentration dependent in vitro induction of apoptosis in stimu lated human lymphocytes and tumor cells of three human cell lines using the most sensitive and specific cytometric method for at present apoptosis det ermination - the indirect TUNEL. BS RNase 50 mug/ml was proven to induce 49 .7, 54 and 68.1% apoptosis in the cells of the ML-2 myeloid cell line and t wo neuroblastoma cell lines: NB-1 and NB-2, respectively. In Con A-stimulat ed human lymphocytes, BS RNase also induced apoptosis, even though not so p ronounced as in human tumor cell lines. In all cultures the induction of ap optosis was proportional to BS RNase concentration ranging from 2-50 mug/ml and correlated with proportional decrease in H-3-thymidine incorporation i nto the newly synthesized DNA. Side by side with the ability of BS RNase to suppress the grouch of human tumors transplanted to nude mice, these biolo gical properties determine this enzyme as a promising agent with potential clinical application.