Mitochondrial uncoupling inhibits p53 mitochondrial translocation in TPA-challenged skin epidermal JB6 cells.

Fei Wang,Xinbin Chen,Xueqi Fu,Yunfeng Zhao,Xia Chen,Robert E Means

doi:10.1371/journal.pone.0013459

Abstract

The tumor suppressor p53 is known to be able to trigger apoptosis in response to DNA damage, oncogene activation, and certain chemotherapeutic drugs. In addition to its transcriptional activation, a fraction of p53 translocates to mitochondria at the very early stage of apoptosis, which eventually contributes to the loss of mitochondrial membrane potential, generation of reactive oxygen species (ROS), cytochrome c release, and caspase activation. However, the mitochondrial events that affect p53 translocation are still unclear. Since mitochondrial uncoupling has been suggested to contribute to cancer development, herein, we studied whether p53 mitochondrial translocation and subsequent apoptosis were affected by mitochondrial uncoupling using chemical protonophores, and further verified the results using a siRNA approach in murine skin epidermal JB6 cells. Our results showed that mitochondrial uncoupling blocked p53 mitochondrial translocation induced by 12-O-tetradecanoylphorbol 13-acetate (TPA), a known tumor promoter to induce p53-mediated apoptosis in skin carcinogenesis. This blocking effect, in turn, led to preservation of mitochondrial functions, and eventually suppression of caspase activity and apoptosis. Moreover, uncoupling protein 2 (UCP2), a potential suppressor of ROS in mitochondria, is important for TPA-induced cell transformation in JB6 cells. UCP2 knock down cells showed enhanced p53 mitochondrial translocation, and were less prone to form colonies in soft agar after TPA treatment. Altogether, our data suggest that mitochondrial uncoupling may serve as an important regulator of p53 mitochondrial translocation and p53-mediated apoptosis during early tumor promotion. Therefore, targeting mitochondrial uncoupling may be considered as a novel treatment strategy for cancer.

Highlights

Most of the cell’s redox reactions take place in mitochondria, which supply cellular energy by oxidating the major products of glucose, pyruvate, and NADH
Our study showed a rapid mitochondrial p53 increase at 1 h that remained throughout the 24-h time course post tetradecanoylphorbol 13-acetate (TPA) treatment (Fig. 1A, lower panel)
Given the strong correlation between p53 and downstream apoptotic events, we further examined whether blocking p53 mitochondrial translocation by mitochondrial uncoupling affected mitochondrial functions and apoptosis

Summary

Introduction

Most of the cell’s redox reactions take place in mitochondria, which supply cellular energy by oxidating the major products of glucose, pyruvate, and NADH. Substrate oxidation in this cellular respiration process generates a proton gradient across the mitochondrial inner membrane that establishes the electrochemical potential (Dym). The energy contained in Dym is mainly used for ATP synthesis (oxidative phosphorylation). Not all of the energy available in the electrochemical gradient is coupled to ATP synthesis. Some of the energy is consumed by ‘‘proton leak’’ reactions, by which protons pumped out of the matrix are able to reflow back along the proton gradient through proton conductance pathways in the inner membrane that bypass the ATP synthase. The nonproductive proton leak termed mitochondrial uncoupling is physiologically important and accounts for 20–25% of basal metabolic rate [5,6]

Methods

Results

Conclusion