Identification of dihydropyrimidinase-related protein 4 as a novel target of the p53 tumor suppressor in the apoptotic response to DNA damage.

The p53 tumor suppressor gene, which is frequently mutated in a wide variety of tumors, plays an important role in maintaining genomic integrity. Following genotoxic insults, the protein level of p53 is increased, and p53 functions as a sequence-specific transcription factor that regulates the expression of downstream target genes required for cell cycle arrest, DNA repair or apoptosis. However, the mechanism for p53-inducible apoptosis remains largely unclear. To search novel downstream targets of p53 on apoptosis, we had carried out microarray analysis. We identified dihydropyrimidinase-related protein (DPYSL) 4 gene, which was upregulated by overexpressing p53 in p53-deficient cells. Both mRNA and protein expressions of DPYSL4 were specifically induced by anticancer agents in p53-proficient cells. Further analyses demonstrated that DPYSL4 was a direct target for p53. We also found that genotoxic-induced apoptosis was repressed in cells silenced for DPYSL4. These findings indicate that DPYSL4 is a novel apoptosis-inducible factor controlled by p53 in response to DNA damage.

D4S234E, a novel p53-responsive gene, induces apoptosis in response to DNA damage.

Understanding intracellular transduction pathways on apoptosis is indispensable for clinical application to develop effective cancer therapies. Transcription factor p53 is activated in response to genotoxic damage and plays crucial roles in apoptosis. p53 regulates the expression of numerous apoptosis-related genes to induce cell death. Here, through genome-wide comprehensive gene expression profile, we identified D4S234E as a novel p53-responsive gene. We determined the p53-binding region in the D4S234E promoter, which is important for p53 regulation in response to DNA damage. Inhibition of D4S234E expression by RNA interference suppressed apoptosis. Furthermore, we observed that D4S234E partially localizes in the endoplasmic reticulum (ER). We found a functional ER retention signal in D4S234E and, more importantly, ER targeting is essential for D4S234E-mediated apoptosis. Finally, depletion of D4S234E diminished genotoxic stress-induced reduction of Bcl-2 and augmentation of CHOP. We thus concluded that a novel p53-responsive gene D4S234E is accumulated in the ER and induces apoptosis in response to DNA damage.