Protein phosphatase Mg2+/Mn2+ dependent 1F promotes smoking-induced breast cancer by inactivating phosphorylated-p53-induced signals

Abstract

// Shih-Hsin Tu 1, 2, 3 , Yin-Ching Lin 4 , Chi-Cheng Huang 1, 5, 6 , Po-Sheng Yang 7, 8 , Hui-Wen Chang 9 , Chien-Hsi Chang 9 , Chih-Hsiung Wu 1, 10 , Li-Ching Chen 2, 3, 11 , Yuan-Soon Ho 4, 9, 12, 13 1 Department of Surgery, School of Medicine, College of Medicine, Taipei Medical University, Taipei, Taiwan 2 Breast Medical Center, Taipei Medical University Hospital, Taipei, Taiwan 3 Taipei Cancer Center, Taipei Medical University, Taipei, Taiwan 4 Graduate Institute of Medical Sciences, College of Medicine, Taipei Medical University, Taipei, Taiwan 5 School of Medicine, College of Medicine, Fu-Jen Catholic University, New Taipei City, Taiwan 6 Breast Center, Cathay General Hospital, Taipei, Taiwan 7 Department of Surgery, Mackay Memorial Hospital, Taipei, Taiwan 8 Department of Medicine, Mackay Medical College, New Taipei City, Taiwan 9 Department of Laboratory Medicine, Taipei Medical University Hospital, Taipei, Taiwan 10 Department of Surgery, En Chu Kong Hospital, New Taipei City, Taiwan 11 Graduate Institute of Clinical Medicine, College of Medicine, Taipei Medical University, Taipei, Taiwan 12 Comprehensive Cancer Center of Taipei Medical University, Taipei, Taiwan 13 School of Medical Laboratory Science and Biotechnology, College of Medical Science and Technology, Taipei Medical University, Taipei, Taiwan Correspondence to: Li-Ching Chen, email: [e-mail] Yuan-Soon Ho, email: [e-mail] Keywords: protein phosphatase Mg 2+ /Mn 2+ dependent 1F, breast cancer, smoking, α9-nicotinic acetylcholine receptor, p53 Received: August 15, 2016      Accepted: October 04, 2016      Published: October 18, 2016 ABSTRACT We previously demonstrated that the activation of α9-nicotinic acetylcholine receptor (α9-nAchR) signaling by smoking promotes breast cancer formation. To investigate the downstream signaling molecules involved in α9-nAChR-induced breast tumorigenesis, we used real-time polymerase chain reactions and Western blotting to assess expression of protein phosphatase Mg 2+ /Mn 2+ dependent 1F (PPM1F), a Ser/Thr protein phosphatase, in human breast cancer samples (n=167). Additionally, stable PPM1F -knockdown and -overexpressing cell lines were established to evaluate the function of PPM1F. The phosphatase activity of PPM1F in nicotine-treated cells was assessed through Western blotting, confocal microscopy, and fluorescence resonance energy transfer. Higher levels of PPM1F were detected in the breast cancer tissues of heavy smokers (n=7, 12.8-fold) greater than of non-smokers (n= 28, 6.3-fold) (**p=0.01). In vitro , nicotine induced PPM1F expression, whereas α9-nAChR knockdown reduced the protein expression of PPM1F. A series of biochemical experiments using nicotine-treated cells suggested that the dephosphorylation of p53 (Ser-20) and BAX (Ser-184) by PPM1F is a critical posttranslational modification, as observed in breast cancer patients who were heavy smokers. These observations indicate that PPM1F may be a mediator downstream of α9-nAChR that activates smoking-induced carcinogenic signals. Thus, PPM1F expression could be used for prognostic diagnosis or inhibited for cancer prevention and therapy.