SET antagonist enhances the chemosensitivity of non-small cell lung cancer cells by reactivating protein phosphatase 2A

Abstract

// Man-Hsin Hung 3, 4, 5, 6 , Cheng-Yi Wang 8 , Yen-Lin Chen 9 , Pei-Yi Chu 10 , Yung-Jen Hsiao 1 , Wei-Tien Tai 1, 2 , Ting-Ting Chao 8 , Hui-Chuan Yu 1 , Chung-Wai Shiau 7 , Kuen-Feng Chen 1, 2 1 Department of Medical Research, National Taiwan University Hospital, Zhongzheng District, Taiwan 2 National Center of Excellence for Clinical Trial and Research, National Taiwan University Hospital, Zhongzheng District, Taiwan 3 Division of Medical Oncology, Department of Oncology, Taipei Veterans General Hospital, Taipei City, Taiwan 4 Division of Hematology and Oncology, Department of Medicine, Taipei Veterans General Hospital, Taipei City, Taiwan 5 Program in Molecular Medicine, School of Life Science, National Yang-Ming University, Taipei City, Taiwan 6 School of Medicine, National Yang-Ming University, Taipei City, Taiwan 7 Institute of Biopharmaceutical Sciences, National Yang-Ming University, Taipei City, Taiwan 8 Medical Research Center, Cardinal Tien Hospital, Fu Jen Catholic University, New Taipei, Taiwan 9 Department of Pathology, Cardinal Tien Hospital, Fu Jen Catholic University, New Taipei, Taiwan 10 Department of Pathology, Show Chwan Memorial Hospital, Changhua City, Taiwan Correspondence to: Chung-Wai Shiau, e-mail: cwshiau@ym.edu.tw Kuen-Feng Chen, e-mail: kfchen1970@ntu.edu.tw Keywords: SET, protein phosphatase 2A, non-small cell lung cancer, chemoresistance, Akt Received: May 20, 2015      Accepted: October 30, 2015      Published: November 13, 2015 ABSTRACT SET is known as a potent PP2A inhibitor, however, its oncogenic role including its tumorigenic potential and involvement in the development of chemoresistance in non-small cell lung cancer (NSCLC) has not yet been fully discussed. In present study, we investigated the oncogenic role of SET by SET-knockdown and showed that SET silencing impaired cell growth rate, colony formation and tumor sphere formation in A549 cells. Notably, silencing SET enhanced the pro-apoptotic effects of paclitaxel, while ectopic expression of SET diminished the sensitivity of NSCLC cells to paclitaxel. Since the SET protein was shown to affect chemosensitivity, we next examined whether combining a novel SET antagonist, EMQA, sensitized NSCLC cells to paclitaxel. Both the in vitro and in vivo experiments suggested that EMQA and paclitaxel combination treatment was synergistic. Importantly, we found that downregulating p-Akt by inhibiting SET-mediated protein phosphatase 2A (PP2A) inactivation determined the pro-apoptotic effects of EMQA and paclitaxel combination treatment. To dissect the critical site for EMQA functioning, we generated several truncated SET proteins. By analysis of the effects of EMQA on the binding affinities of different truncated SET proteins to PP2A-catalytic subunits, we revealed that the 227–277 amino-acid sequence is critical for EMQA-induced SET inhibition. Our findings demonstrate the critical role of SET in NSCLC, particularly in the development of chemoresistance. The synergistic effects of paclitaxel and the SET antagonist shown in current study encourage further validation of the clinical potential of this combination.