P53-DEPENDENT AND P53-INDEPENDENT REGULATION OF THE DEATH RECEPTOR KILLER DR5 GENE-EXPRESSION IN RESPONSE TO GENOTOXIC STRESS AND TUMOR-NECROSIS-FACTOR-ALPHA/

The death receptor (DR) KILLER/DR5 gene has recently been identified a s a doxorubicin-regulated transcript that was also induced by exogenou s wild-type p53 in p53-negative cells. KILLER/DR5 gene encodes a DR co ntaining cell surface protein that is highly homologous to DR4, anothe r DR of the tumor necrosis factor (TNF) receptor family, Both DR4 and KILLER/DR5 independently bind to their specific Ligand TRAIL and engag e the caspase cascade to induce apoptosis. TRID (also known as TRAIL-R 3) is an antiapoptotic decoy receptor that lacks the cytoplasmic death domain and competes with KILLER/DR5 and DR4 for binding to TRAIL. In this study, we demonstrate that the DR KILLER/DR5 gene is regulated in a p53-dependent and -independent manner during genotoxic and nongenot oxic stress-induced apoptosis. Just like other p53-regulated genes, io nizing radiation induction of KILLER/DR5 occurs in p53 wild-type cells , whereas methyl methanesulfonate regulation of KILLER/DR5 occurs in a p53-dependent and -independent manner. However, unlike other p53-regu lated genes, KILLER/DR5 is not regulated following UV irradiation, TNF -alpha, a nongenotoxic cytokine, also induced the expression of KILLER /DR5 in a number of cancer cell lines, irrespective of p53 status. TNF -alpha did not alter the KILLER/DR5 mRNA stability, suggesting that th e TNF-alpha regulation of KILLER/DR5 expression appears transcriptiona l. We also provide evidence that KILLER/DR5 is regulated in a trigger and cell type-specific manner and that its induction by TNF-alpha, p53 , or DNA damage is not the consequence of apoptosis induced by these a gents. Unlike KILLER/DR5, none of the other KILLER/DR5 family members, including DR4, TRID, or the ligand TRAIL, displayed genotoxic stress or TNF-alpha regulation in a p53 transcription-dependent manner. Thus, KILLER/DR5 appears a bona fide downstream target of p53 that is also regulated in a cell type-specific, trigger-dependent, and p53-independ ent manner.