Molecular mechanism of Akt signaling evoked by 1, 2-naphthoquinone

[Speaker] Kengo Nakahara:1
[Co-author] Hideki Hiraoka:1, Kyohei Hamada:1, Yoshito Kumagai:2, Takashi Uehara:1
1:Graduate School of Medicine Dentistry and Pharmaceutical Sciences, Okayama University, Japan, 2:Doctoral Program in Biomedical Sciences, Graduate School of Comprehensive Human Sciences, University of Tsukuba, Japan

[Background] The redox-mediated chemical modification occurs via oxidative reaction between electrophile and cysteine thiol in the presence of an electron acceptor. It is widely recognized that long exposure to or high concentration of 1,2-naphthoquinone (1,2-NQ), an electrophile in cigarette ingredients/smoke or metabolite of naphthalene, results in cytotoxic effect. Whereas, low concentration of 1,2-NQ specifically stimulates Akt signaling involving cell proliferation and anti-apoptosis possibly via protein oxidation. In this study, we addressed to clarify the effects of 1,2-NQ, in PI3K-Akt pathway involved in cell proliferation and anti-apoptosis.
[Methods] We performed western blotting to detect phosphorylation of Akt, EGFR, IGF-IR, Insulin receptor using specific antibodies. To assess cell viability, we conducted WST-8 assay and hoechst33258 staining.
[Results] Phosphorylation of Akt was observed by treatment with 1,2-NQ in A549 cells in a concentration-dependent manner. This activation was sensitive to wortmannin (PI3K inhibitor) and OSU-03012 (PDK1 inhibitor). Then, we found that 1,2-NQ stimulated the phosphorylation of EGFR, but not IGF-IR and Insulin receptor. Moreover, activation of Akt by 1,2-NQ was almost suppressed by pretreatment of tyrphostinA25, a specific EGFR tyrosine kinase inhibitor. Akt activation contributes to protect the apoptotic cell death of A549 cells induced by serum deprivation possibly via Bad phosphorylation.
[Conclusions] These findings showed that treatment with appropriate amount of 1,2-NQ leads to anti-apoptotic action through PI3K-Akt signaling via EGFR.

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