Mutant p53 protein is highly expressed in most cancer cells due to its protein stabilization. Mutant p53 loses wild-type p53 function but gains new oncogenic functions in driving tumor growth and drug resistance. Depletion of mutant p53 is an attractive strategy for cancer therapy. We reported a small-molecule NSC59984 destabilizes mutant p53 protein via protein degradation (Zhang et al., Cancer Research, 2015). In this study, we demonstrate that the ERK2 pathway plays a specific role in NSC59984-induced mutant p53 degradation via MDM2-mediated ubiquitination. We observe a sustained-phosphorylation of ERK1/2 in cancer cells treated with NSC59984. ERK1/2 pathway is negatively regulated by MKP-1. We find that MKP-1 activity is partially inhibited by NSC59984 in a dose dependent manner in vitro. These results suggest that NSC5998 sustains ERK1/2 phosphorylation partially via disruption of the feedback-loop between MKP-1 and ERK2 pathway. Knockdown of ERK2 rescues mutant p53 from NSC59984-mediated degradation, and inhibits NSC59984-restoration of p53 signaling in mutant p53-expressing cells. On the contrary, the effect of NSC59984 on the mutant p53 is not inhibited by the blockage of JNK and P38, two pathways negatively regulated by MKP-1. These results suggest that the ERK2 phosphorylation is specifically required for NSC59984-mediated mutant p53 degradation. We further find that NSC59984 induces ERK2-dependent MDM2 phosphorylation. The effect of NSC59984 on MDM2 phosphoryation is partially inhibited by the blockage of ERK2 signaling (via U0126 treatment or Knockdown of ERK2), not by the attenuation of the JNK pathway. Furthermore, NSC59984-mediated mutant p53 protein degradation is inhibited by MDM2 knockdown, and enhanced by MDM2 overexpression in cancer cells. NSC59984-increased ubiquitination of mutant p53 is attenuated by U0126. Our results suggest that the ERK2 signaling pathway-MDM2 axis is a major determinant of NSC59984-mediated mutant p53 degradation. We further demonstrate that NSC59984 induces cell death via apoptosis, and NSC59984-induced cell death is mainly rescued by inhibition of the ERK2 pathway in p53 mutant cancer cells. Taken together, our results suggest that phosphorylated-ERK2 is an important factor required for NSC59984-mediated mutant p53 degradation which may further contribute to NSC59984-induced cell death in cancer cells.

Citation Format: Shengliang Zhang, Lanlan Zhou, David Dicker, Wafik S. El-Deiry. NSC59984 induces mutant p53 degradation via activating ERK2 pathway-MDM2 axis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 2156. doi:10.1158/1538-7445.AM2017-2156