Regulation of p53 by reversible post-transcriptional and post-translational mechanisms in liver and skeletal muscle of an anoxia tolerant turtle, Trachemys scripta elegans.

The red-eared slider turtle (Trachemys scripta elegans) exhibits well-developed natural anoxia tolerance that depends on multiple biochemical adaptations, including anoxia-induced hypometabolism. We hypothesized that signaling by the p53 protein could aid in establishing the hypometabolic state by arresting the cell cycle, protecting against DNA damage as well as altering pathways of energy metabolism. Immunoblotting was used to evaluate the regulation and post-transcriptional modifications of p53 in liver and skeletal muscle of red-eared slider turtles subjected to 5h or 20h of anoxic submergence. Tissue specific regulation of p53 was observed with the liver showing a more rapid activation of p53 in response to anoxia as well as differential expression of seven serine phosphorylation and two lysine acetylation sites when compared with skeletal muscle. Protein expression of MDM2, a major p53 inhibitor, was also examined but did not change during anoxia. Reverse-transcriptase PCR was used to assess transcript levels of selected p53 target genes (14-3-3σ, Gadd45α and Pgm) and one microRNA (miR-34a); results showed down-regulation of Pgm and up-regulation of the other three. These findings show an activation of p53 in response to anoxia exposure and suggest an important role for the p53 stress response pathway in regulating natural anoxia tolerance and hypometabolism in a vertebrate facultative anaerobe.