APOPTOSIS INDUCED BY DIFFERENTIATION OR SERUM DEPRIVATION IN AN IMMORTALIZED CENTRAL-NERVOUS-SYSTEM NEURONAL CELL-LINE

To characterize the nature of programmed cell death (PCD) induced in n euronal cells during development, three regulators of apoptosis were i nvestigated: one, the bcl-2-related genes, modulate cell survival, and the other two, the interleukin-1 beta converting enzyme (ICE)-related enzymes and the tumor suppressor protein p53, have been implicated as mediators of apoptosis. These regulators were studied in H19-7 cells, an SV40 T-ts-immortalized rat hippocampal neuronal cell line that can be differentiated with basic fibroblast growth factor at the nonpermi ssive temperature, resulting in a rapid attrition of cells by apoptosi s. PCD occurred by two mechanisms in H19-7 cells: The first was initia ted by removal of serum from undifferentiated cells, and the second wa s a consequence of neuronal differentiation. In differentiated H19-7 c ells, the survival time was increased by both human bcl-2 and bcl-x(L) , and this could be reversed by bcl-x(s). Addition of a peptide inhibi tor of the ICE enzyme family to H19-7 cells resulted in a transient pr otection against differentiation-associated apoptosis, whereas no furt her protection was observed in the BCL-2- or BCL-X(L)-expressing cells . Shifting the differentiated cells to 33 degrees C to inactivate p53 did not significantly affect the apoptotic process, indicating that ap optosis induced by neuronal differentiation is not dependent on the co ntinued presence of p53. By contrast, in undifferentiated cells, cell loss induced by transfer to serum-free media occurred more rapidly on inactivation of large T, consistent with p53 involvement. This medium- induced decrease in cell survival could not be rescued by the ICE inhi bitor but was partially rescued by BCL-2 or BCL-X,. Furthermore, studi es involving expression of BCL-2 and BCL-X(L) alone or together reveal ed differences in the survival dependent on the cellular environment. These results suggest that apoptosis of neuronal cells occurs by at le ast two processes: one in undifferentiated cells initiated by removal of serum and one linked to differentiation. The data implicate the ICE enzyme family but not p53 in apoptosis induced by differentiation and demonstrate that either BCL-2 or BCL-X(L) can prolong the survival of differentiated neuronal cells.