UNC5H4 is a netrin-1 receptor UNC5H family member. In this study, we found that UNC5H4 is a direct transcriptional target of p53. During adriamycin (ADR)-mediated apoptosis, UNC5H4 was significantly induced in p53-proficient U2OS cells but not in p53-deficient H1299 cells. Enforced expression of p53 induced UNGH4. Consistent with these results, siRNA-mediated knockdown of p53 in U2OS cells attenuated ADR-dependent induction of UNGH4. indeed, we found four putative p53-responsive elements within intron I of UNC5H4 gene. Luciferase reporter assay and ChIP analysis demonstrated that, among them, two tandem elements respond to exogenous p53 which is efficiently recruited onto them. Furthermore, enforced expression of UNC5H4 remarkably reduced number of drug-resistant colonies in p53-proficient cells but not in p53-deficient cells, suggesting that UNC5H4-induced apoptosis is dependent on p53 status. siRNA-mediated knockdown of UNC5H4 rendered U2OS cells resistant to ADR. Collectively, our present results suggest that UNC5H4 amplifies p53-dependent apoptotic response. (c) 2008 Elsevier Inc. All rights reserved.