CELL SUICIDE IN STARVING HYBRIDOMA CULTURE - SURVIVAL-SIGNAL EFFECT OF SOME AMINO-ACIDS

Two mouse hybridoma cell lines cultured in different basal media with the iron-rich protein-free supplement were subjected to deliberate sta rvation by inoculation into media diluted with saline to 50% or less. In the diluted media the growth was markedly suppressed and a large fr action of cells died by apoptosis. The cells could be rescued from apo ptotic death by individual additions of amino acids, such as glycine, L-alanine, L-serine, L-threonine, L-proline, L-asparagine, L-glutamine , L-histidine, D-serine, beta-alanine or taurine. Amino acids with hyd rophobic or charged side chains were without effect. The apoptosis pre venting activity manifested itself even in extremely diluted media, do wn to 10% of the standard medium. The activity of L-alanine in the pro tection of cells starving in 20% medium was shown also in semicontinuo us culture. In the presence of 2 mM L-alanine the steady-state viable cell density more than doubled, with respect to control, and the apopt otic index dropped from 37% in the control to 16%. It was concluded th at the apoptosis-preventing amino acids acted as signal molecules, rat her than nutrients, and that the signal had a character of a survival factor. The specificity of present results, obtained with two differen t hybridomas, supports our view (Franek and Chladkova-Sramkova, 1995) that the membrane transport macromolecules themselves may play the rol e of the recognition elements in a signal transduction pathway control ling the survival of hybridoma cells.