NR4A1-induced increase in the sensitivity of a human gastric cancer line to TNF alpha-mediated apoptosis is associated with the inhibition of JNK/Parkin-dependent mitophagy

Tumor necrosis factor alpha (TNF alpha)-based immunotherapy is the vital host defense system against the progression of gastric cancer (GC) as a pro-inflammatory and pro-apoptotic cytokine. However, resistance limits its therapeutic efficiency. Therefore, an increasing number of studies are focusing on the development of drugs or methods with which to enhance the treatment efficacy of TNF alpha. Nuclear receptor subfamily 4 group A member 1 (NR4A1) has been shown to exert antitumor effects through several mechanisms, such as by inhibiting proliferation, as well as pro-apoptotic and potent pro-oxidant effects. In this study, we examined the effects and mechanisms of action of NR4A1 on the apoptosis of GC cells treated with TNF alpha, with particular focus on mitochondrial homeostasis. We found that TNF alpha treatment decreased NR4A1 expression. Moreover, the overexpression of NR4A1 in the presence of TNF alpha further increased GC cell apoptosis. Mechanistically, the overexpression of NR4A1 augmented caspase-9-dependent mitochondrial apoptosis, as evidenced by reduced mitochondrial membrane potential, reactive oxygen species (ROS) overproduction, mitochondrial permeability transition pore (mPTP) opening and the leakage of cytochrome c (Cyt-c) leakage. Moreover, NR4A1 overexpression also evoked mitochondrial energy disorder via the suppression of mitochondrial respiratory complex expression. Furthermore, we found that TNFa treatment activated Parkin-dependent mitophagy. Excessive Parkin-dependent mitophagy blocked mitochondrial apoptosis, undermining the toxic effects of TNF alpha on cells. However, NR4A1 overexpression suppressed Parkin-dependent mitophagy via the inhibition of c-Jun N-terminal kinase (JNK). Re-activation of the JNK/Parkin pathway abrogated the inhibitory effects of NR4A1 on mitophagy, eventually limiting cell apoptosis. Collectively, this study confirmed that NR4A1 sensitizes GC cells to TNF alpha-induced apoptosis through the inhibition of JNK/Parkin-dependent mitophagy.