Polysulfide Na2S4 regulates the activation of PTEN/Akt/CREB signaling and cytotoxicity mediated by 1,4-naphthoquinone through formation of sulfur adducts

Electrophiles can activate redox signal transduction pathways, through actions of effector molecules ( e.g ., kinases and transcription factors) and sensor proteins with low p K a thiols that are covalently modified. In this study, we investigated whether 1,4-naphthoquinone (1,4-NQ) could affect the phosphatase and tensin homolog (PTEN)–Akt signaling pathway and persulfides/polysulfides could modulate this adaptive response. Simultaneous exposure of primary mouse hepatocytes to Na 2 S 4 and 1,4-NQ markedly decreased 1,4-NQ-mediated cell death and S -arylation of cellular proteins. Modification of cellular PTEN during exposure to 1,4-NQ was also blocked in the presence of Na 2 S 4 . 1,4-NQ, at up to 10 µM, increased phosphorylation of Akt and cAMP response element binding protein (CREB). However, at higher concentrations, 1,4-NQ inhibited phosphorylation of both proteins. These bell-shaped dose curves for Akt and CREB activation were right-shifted in cells treated with both 1,4-NQ and Na 2 S 4 . Incubation of 1,4-NQ with Na 2 S 4 resulted in formation of 1,4-NQ–S–1,4-NQ-OH. Unlike 1,4-NQ, authentic 1,4-NQ-S-1,4-NQ-OH adduct had no cytotoxicity, covalent binding capability nor ability to activate PTEN-Akt signaling in cells. Our results suggested that polysulfides, such as Na 2 S 4 , can increase the threshold of 1,4-NQ for activating PTEN–Akt signaling and cytotoxicity by capturing this electrophile to form its sulfur adducts.