Acute and chronic neurodegeneration, for example, following brain injury or Alzheimer's disease, is characterized by programmed death of neuronal cells. The present study addresses the role and interaction of p53- and NF-kappaB-dependent mechanisms in delayed neurodegeneration following traumatic brain injury (TBI). After experimental TBI in mice p53 rapidly accumulated in the injured brain tissue and translocated to the nucleus of damaged neurons, whereas NF-kappaB transcriptional activity simultaneously declined. Post-traumatic neurodegeneration correlated with the increase in p53 levels and was significantly reduced by the selective p53 inhibitor pifithrin-alpha (PFT). Strikingly, this protective effect was observed even when PFT treatment was delayed up to 6 h after trauma. Inhibition of p53 activity resulted in the concomitant increase in NF-kappaB transcriptional activity and upregulation of NF-kappaB-target proteins, for example X-chromosomal-linked inhibitor of apoptosis (XIAP). It is interesting to note that inhibition of XIAP abolished the neuroprotective effects of PFT in cultured neurons exposed to camptothecin, glutamate, or oxygen glucose deprivation. In conclusion, delayed neuronal cell death after brain trauma is mediated by p53-dependent mechanisms that involve inhibition of NF-kappaB transcriptional activity. Hence, p53 inhibition provides a promising approach for the treatment of acute brain injury, since it blocks apoptotic pathways and concomitantly triggers survival signaling with a therapeutic window relevant for clinical applications.