Obovatol Induces Apoptosis in Non-small Cell Lung Cancer Cells via C/EBP Homologous Protein Activation Heejeong Kim, 1† Eun Ah Shin, 3† Chang Geun Kim, 3 Dae Young Lee, 4 Bonglee Kim, 3 Nam-In Baek 2 and Sung-Hoon Kim 3 * 1 Department of East West Medical Science, Graduate School of East West Medical Science, Kyung Hee University, Yongin 446-701, Korea 2 Department of Oriental Medicine Biotechnology, Graduate School of Biotechnology, Kyung Hee University, Yongin 446-701, Korea 3 College of Korean Medicine, Kyung Hee University, Seoul 131-701, Korea 4 Department of Herbal Crop Research, National Institute of Horticultural and Herbal Science, Rural Development Administration (RDA), Eumseong 27709, Korea Although obovatol, a phenolic compound from the bark of Magnolia obovata, was known to have antioxidant, neuroprotective, antiinflammatory, antithrombotic and antitumour effects, its underlying antitumour mechanism is poorly understood so far. Thus, in the present study, the antitumour molecular mechanism of obovatol was investigated in non-small cell lung cancer cells (NSCLCs). Obovatol exerted cytotoxicity in A549 and H460 NSCLCs, but not in BEAS-2B cells. Also, obovatol increased sub-G1 accumulation and early and late apoptotic portion in A549 and H460 NSCLCs. Consistently, obovatol cleaved PARP, activated caspase 9/3 and Bax and attenuated the expression of cyclin D1 in A549 and H460 NSCLCs. Interestingly, obovatol upregulated the expression of endoplasmic reticulum stress proteins such as C/EBP homologous protein (CHOP), IRE1α, ATF4 and p-elF2 in A549 and H460 NSCLCs. Conversely, depletion of CHOP blocked the apoptotic activity of obovatol to increase sub-G1 accumulation in A549 and H460 NSCLCs. Overall, our findings support scientific evidences that obovatol induces apoptosis via CHOP activation in A549 and H460 NSCLCs. Copyright © 2016 John Wiley & Sons, Ltd. Keywords: obovatol; apoptosis; caspase; CHOP; non-small cell lung cancer cell. INTRODUCTION Lung cancer has been one of the lethal cancers world- wide. Historically, non-small cell lung cancer (NSCLC) accounts for approximately 87% of lung cancer (Jemal et al., 2011). In general, surgery, radiation therapy, chemotherapy, targeted therapies, immunotherapy and palliative procedures are applied for the NSCLC treatment(Carter and Giaccone, 2012; Sculier, 2013). Most side effects by these treatments are blood clots, bone issues, chemobrain, dental issues, diarrhoea, fatigue, hair loss, lymphedema, neuropathy, pain, diar- rhoea and weight loss(Sculier, 2013). Recently, to reduce side effects and enhance synergistic effect with classical anticancer agents, several herbal extracts(Lin and Li, 2007; Liu et al., 2008; Xu et al., 2014) and compounds(Liang et al., 2007; Tsao et al., 2014; Zhu et al., 2015) were highlighted as NSCLC chemopreven- tive agents or sensitizer to anticancer drugs. As malignant cells struggle to evade apoptosis for their survival and proliferation, apoptosis induction is a good strategy in cancer treatment (Lopez-Beltran et al., 2007; Jia et al., 2012). Apoptosis is primarily induced via the intrinsic pathway mediated by caspase 9/3 while the extrinsic pathway is mediated by cell surface death receptors such as the tumour necrosis factor receptor superfamily (Holoch and Griffith, 2009; Hellwig et al., 2010; Declercq et al., 2011). There are accumulating evidences that the induction of endoplasmic reticulum (ER) stress proteins is involved in apoptosis in lung cancer(Lin et al., 2008; Moriya et al., 2011; Zhao et al., 2011; Kim et al., 2012). Among ER stress proteins, three ER transmembrane proteins such as inositol-requiring enzyme-1 (IRE1), activating transcription factor 6 and PKR-like ER kinase respond to the accumulation of unfolded proteins as survival response (Fels and Koumenis, 2006). In contrast, when stress conditions persist, apoptotic signalling pathways are initiated, triggering the tran- scriptional induction of CHOP/GADD153 or phosphor- ylation of the translation initiation factor eIF-2 (Faitova et al., 2006). Obovatol, a phenolic compound isolated from the bark of M. obovata, was known to have antioxidant (Shen et al., 2009), neuroprotective (Choi et al., 2011), antiinflammatory (Seo et al., 2013) and antithrombotic (Park et al., 2011) activities. Furthermore, obovatol was reported to exhibit antitumour effect in MM6 acute myeloid leukaemia (Kim et al., 2014), LNCaP and PC-3 prostate cancer and SW620 and HCT116 colon cancer via inactivation of NF-kB (Lee et al., 2008; Lee et al., 2009). Nevertheless, its underlying antitumour mecha- nism still remains unclear so far. * Correspondence to: Sung-Hoon Kim, College of Korean Medicine, Kyung Hee University, 1 Hoegi-dong, Dongdaemun-gu, Seoul 130-701, Korea. E-mail: sungkim7@khu.ac.kr † These authors contributed equally to this work. PHYTOTHERAPY RESEARCH Phytother. Res. (2016) Published online in Wiley Online Library (wileyonlinelibrary.com) DOI: 10.1002/ptr.5690 Copyright © 2016 John Wiley & Sons, Ltd. Received 16 May 2016 Revised 03 July 2016 Accepted 11 July 2016