Prion protein gene (Prnp)-deficient(Prnp(-/-)) neuronal cells are more susceptible to serum deprivation compared to Prnp(+/+) neuronal cells. However, little is known about the cell death of Prnp(-/-) neuronal cells under serum deprivation. In this study, as a known neuroprotective agent we analyzed the effect of tumor necrosis factor-alpha (TNF-alpha) on the cell death of Prnp(-/-) neuronal cells. Although expression of Bcl-2 and Bcl-x(L) decreased in a time-dependent manner under serum deprivation, treatment with TNF-alpha protected Prnp(-/-) neuronal cells from serum deprivation with an increase in anti-apoptotic proteins Bcl-2 and Bcl-x(L). Nuclear morphological analysis using fluorescence microscopy and flow cytometry analysis showed that gene transfer of bcl-2 or bcl-x(L) significantly inhibited apoptosis induced by serum deprivation. These findings indicate that TNF-alpha attenuated cell death of Prnp(-/-) neuronal cells by induction of Bcl-2 and Bcl-x(L),and that decreases in Bcl-2 and Bcl-x(L) played crucial roles in the apoptosis of Prnp(-/-) neuronal cells. (C) 2003 Elsevier Inc. All rights reserved.