p22phox confers resistance to cisplatin, by blocking its entry into the nucleus

// Chih-Chang Hung 1, 2, * , Chen-Yu Chien 3, 4, 5, * , Wei-Fan Chiang 6, 7 , Chang-Shen Lin 1 , Tzyh-Chyuan Hour 8 , Hau-Ren Chen 9 , Ling-Feng Wang 3, 10 , Jenq-Yuh Ko 11 , Chi-Hua Chang 12 , Jeff Yi-Fu Chen 2 1 Graduate Institute of Medicine, College of Medicine, Kaohsiung Medical University, Kaohsiung, Taiwan 2 Department of Biotechnology, Kaohsiung Medical University, Kaohsiung, Taiwan 3 Department of Otorhinolaryngology, School of Medicine, College of Medicine, Kaohsiung Medical University, Kaohsiung, Taiwan 4 Department of Otorhinolaryngology, Kaohsiung Medical University Hospital, Kaohsiung, Taiwan 5 Department of Otorhinolaryngology, Kaohsiung Municipal Hsiao-Kang Hospital, Kaohsiung Medical University, Kaohsiung, Taiwan 6 Department of Dentistry, Chi-Mei Medical Center, Liouying, Taiwan 7 Department of Dentistry, School of Dentistry, National Yang-Ming University, Taipei, Taiwan 8 Department of Biochemistry, Kaohsiung Medical University, Kaohsiung, Taiwan 9 Department of Life Science and Institute of Molecular Biology, National Chung Cheng University, Chia-Yi, Taiwan 10 Department of Otorhinolaryngology, Kaohsiung Municipal Ta-Tung Hospital, Kaohsiung Medical University, Kaohsiung, Taiwan 11 Department of Otolaryngology, National Taiwan University, College of Medicine, Taipei, Taiwan 12 Department of Dentistry, Chang Gung Memorial Hospital, Kaohsiung, Taiwan * These authors have contributed equally to this work Correspondence to: Jeff Yi-Fu Chen, e-mail: yifuc@kmu.edu.tw Keywords: p22phox, CDDP resistance, apoptosis, PI3K/Akt, oral squamous cell carcinoma (OSCC) Received: September 30, 2014      Accepted: December 11, 2014      Published: February 19, 2015 ABSTRACT Cisplatin (CDDP) is a potent chemotherapeutic agent but resistance to the drug remains a major challenge in cancer treatment. To evaluate the efficacy of CDDP in oral squamous cell carcinoma (OSCC), we found that p22phox was highly expressed in CDDP-resistant OSCC specimens. Knockdown of p22phox sensitized OSCC cell lines to CDDP ( P < 0.05). Stable overexpression of p22phox augmented CDDP resistance, as evidenced by the significantly higher IC 50 values. This cytoprotective effect was attributed to the abrogation of CDDP-induced apoptosis. Akt phosphorylation was increased in p22phox stable lines. However, blocking PI3K/Akt pathway only partially restored CDDP-induced apoptosis. In addition, the overexpressed p22phox in OSCC cells exhibited cytoplasmic localization with enhanced perinuclear expression, consistent with the localization pattern in OSCC specimens. Remarkably, CDDP entry into the nucleus was severely impaired in p22phox-overexpressing cells ( P < 0.001), and cytoplasmically accumulated CDDP was co-localized with overexpressed p22phox. This was supported by decreased CDDP-DNA adduct formation and delayed chk1-p53 signaling activation. Together, overexpression of p22phox sequestered CDDP and caused defective CDDP entry into the nucleus, significantly attenuating CDDP-induced apoptosis. Such diminished apoptosis was further abolished by p22phox-activating PI3K/Akt pathway. Our work has suggested a novel biomarker and insight into the mechanism of CDDP resistance.