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 pancreatic ribonuclease has been proven to have important biological properties as aspermatogenic, antitumor, embryotoxic and immunosuppressive activities. Recently we published preliminary results concerning the ability of bovine seminal 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. In this study we bring more confirmative data concerning the concentration dependent in vitro induction of apoptosis in stimulated human lymphocytes and tumor cells of three human cell lines using the most sensitive and specific cytometric method for at present apoptosis determination the indirect TUNEL. BS RNase 50 microg/ml was proven to induce 49.7, 54 and 68.1% apoptosis in the cells of the ML-2 myeloid cell line and two neuroblastoma cell lines: NB-1 and NB-2, respectively. In Con A-stimulated human lymphocytes, BS RNase also induced apoptosis, eventhough not so pronounced as in human tumor cell lines. In all cultures the induction of apoptosis was proportional to BS RNase concentration ranging from 2-50 microg/ml and correlated with proportional decrease in 3H-thymidine incorporation into the newly synthesized DNA. Side by side with the ability of BS RNase to suppress the growth of human tumors transplanted to nude mice, these biological properties determine this enzyme as a promising agent with potential clinical application.