Low levels of hepatic selenium (Se)-dependent glutathione peroxidase 1 (GPX1) activity have been shown to protect against oxidative liver injury in Se-deficient mice. The objective of the present study was to determine if the GPX1 protection was associated with phosphorylations of c-Jun N-terminal kinase (JNK) and p53 on Ser-15, two key signalling events in oxidative-stress-mediated cell death. Both Se-deficient GPX1 knockout (GPX1-/-) and wild-type (WT) mice (n = 64) were pretreated with an intraperitoneal injection of Se (as sodium selenite, 50μg/kg body weight) 6h before an intraperitoneal injection of paraquat (12.5mg/kg). Liver aponecrosis, a mixed form of cell death sharing apoptosis and necrosis, was induced by paraquat in both groups of mice. However, its appearance was remarkably delayed and the severity was decreased by the repletion of hepatic GPX1 activity to <4% of the normal level by the Se injection in the WT mice, compared with that in the GPX1-/- mice. Consistently, the WT mice had lower levels of hepatic phospho-JNK, p53 and phospho-p53 (Ser-15) when compared with the GPX1-/- mice at 1—10h after paraquat injection. Incubating liver homogenates with antibodies raised against JNK or phospho-JNK resulted in co-immunoprecipitation of phospho-p53 (Ser-15), and the amounts of the precipitated phospho-p53 were greater in the GPX1-/- mice when compared with that in the WT mice. The co-precipitated complex by the anti-phospho-JNK antibody was capable of phosphorylating intrinsic or extrinsic p53 on Ser-15. In conclusion, phospho-JNK may catalyse phosphorylation of p53 on Ser-15 in Se-deficient mouse liver under moderate oxidative stress, and attenuation of that cascade by low levels of GPX1 activity is associated with its protection against the pro-oxidant-induced liver aponecrosis.
Abbreviations used: GPX1, glutathione peroxidase 1; GPX1-/-, GPX1 knockout; GST, glutathione S-transferase; JNK, c-Jun N-terminal kinase; MAPK, mitogen-activated protein kinase; ROS, reactive oxygen species; TUNEL, terminal transferase deoxytidyl uridine end labelling; WT, wild-type.