SURVIVAL AND DEATH OF PRELYMPHOMATOUS B-CELLS FROM N-MYC BCL-2 DOUBLETRANSGENIC MICE CORRELATES WITH THE REGULATION OF INTRACELLULAR CA2+ FLUXES/

Coexpression of the proto-oncogenes c-myc and bcl-2 under the control of the immunoglobulin enhancer E mu provokes the rapid development of primitive lymphoid tumors in transgenic mice, In the present study we show that the myc family members N-myc and L-myc also cooperate with b cl-2 in oncogenesis and can provoke the development of more mature pre -B, B and T cell type lymphomas. The analysis of prelymphomatous B-cel ls from single E mu N-myc and bcl-2-Ig transgenic animals and from you ng, tumor free, double transgenic E mu N-myc/bcl-2-Ig mice revealed th at E mu directed expression of N-myc leads to very rapid apoptosis aft er explantation and culturing compared to B-cells from normal mice. As expected, B-cells from bcl-2-Ig transgenics were protected to a certa in degree from apoptosis, Strikingly however, B-cells from E mu N-myc/ bcl-2-Ig double transgenic animals were found to be almost completely resistant towards a number of different apoptotic stimuli. Furthermore , after treatment with H2O2, which can trigger apoptosis, B-cells from E mu N-myc animals reach levels of intracellular free Ca2+ concentrat ions that are comparable to B-cells from normal mice, whereas B-cells from bcl-2-Ig or E mu N-myc/bcl-2-Ig double transgenic mice show no in crease in intracellular Ca2+ concentrations after stimulation with H2O 2. These findings suggest that the prevention of apoptosis conferred b y bcl-2 correlates with the inhibition of intracellular Ca2+ fluxes wh ereas induction of apoptosis mediated by N-myc requires normal Ca2+ le vels. We hypothesize therefore that the regulation of intracellular Ca 2+ concentrations represent one important parameter in the oncogenic c ooperation between bcl-2 and N-myc.