Gadd45β is transcriptionally activated by p53 via p38α-mediated phosphorylation during myocardial ischemic injury

Growth arrest and DNA damage-inducible 45 beta (Gadd45 beta) have been shown to play a role in inducing cardiomyocyte apoptosis under ischemia/anoxia. The well-known transcription factor p53 is known to cause apoptosis in cardiomyocytes under ischemia. Based on the common role of Gadd45 beta and p53 in ischemia-induced apoptosis, we investigated whether p53 is involved in the mechanisms responsible for Gadd45 beta expression in both in vitro and in vivo models of ischemic heart injury. A chromatin immunoprecipitation assay revealed direct binding of p53 to the Gadd45 beta promoter region during anoxia, and this binding was confirmed by surface plasmon resonance imaging. In rat heart-derived H9c2 cells, silencing of p53 abrogated the increase of Gadd45 beta promoter-luciferase reporter (Gadd45 beta-Luc) activity and the expression of Gadd45 beta under anoxia and overexpression of p53 enhanced Gadd45 beta-Luc activity and Gadd45 beta expression. Gadd45 beta mRNA and protein expression were significantly inhibited by p53 siRNA in a rat ischemic heart model. In addition, p38 alpha-mediated phophorylation of p53 at both Ser15 and Ser20 was shown to be essential for the expression of Gadd45 beta mRNA and protein during anoxia. These results reveal the p38 alpha-p53-Gadd45 beta axis as a novel signaling module in the anoxia-induced apoptotic death pathway. In conclusion, this study provides molecular evidence that Gadd45 beta is a novel downstream target gene of p53 under ischemia/anoxia and suggests the therapeutic potential of targeting Gadd45 beta as a treatment of ischemic heart injury. Gadd45 beta is transcriptionally induced by p53 via direct binding under ischemia/anoxia. The induction of Gadd45 beta expression requires the p53 phosphorylation at Ser15/Ser20. p38 alpha mediates the p53 phosphorylation at Ser15/Ser20 and the Gadd45 beta expression. Ischemia/anoxia-p38 alpha-p53-Gadd45 beta axis serves as a novel apoptotic signaling module.