Am J Cancer Res 2018;8(9):1812-1822 www.ajcr.us /ISSN:2156-6976/ajcr0082503 Original Article Preprogramming therapeutic response of PI3K/mTOR dual inhibitor via the regulation of EHMT2 and p27 in pancreatic cancer Yu-Feng Tian1,2, Hui-Ching Wang3,4, Chi-Wen Luo5, Wen-Chun Hung6, Yu-Han Lin3, Tzu-Yi Chen3, Chien-Feng Li7,8,9, Chen-Yi Lin10, Mei-Ren Pan3 1Division of Colorectal Surgery, Department of Surgery, Chi-Mei Medical Center, Tainan, Taiwan; 2Department of Health and Nutrition, Chia Nan University of Pharmacy and Science, Tainan, Taiwan; 3Graduate Institute of Clinical Medicine, College of Medicine, Kaohsiung Medical University, Kaohsiung, Taiwan; 4Division of Hematology and Oncology, Department of Internal Medicine, Kaohsiung Medical University Hospital, Kaohsiung Medical University, Kaohsiung, Taiwan; 5Division of Cardiology, Chang Gung Memorial Hospital-Kaohsiung Medical Center, Kaohsiung, Taiwan; 6National Institute of Cancer Research, National Health Research Institutes, Tainan 704, Taiwan; 7De- partment of Pathology, Chi Mei Medical Center, Tainan, Taiwan; 8National Institute of Cancer Research, National Health Research Institutes, Tainan, Taiwan; 9Department of Biotechnology, Southern Taiwan University of Science and Technology, Tainan, Taiwan; 10Division of Gastroenterology and Hepatology, Department of Internal Medicine, Chi-Mei Medical Center, Tainan, Taiwan Received July 12, 2018; Accepted August 14, 2018; Epub September 1, 2018; Published September 15, 2018 Abstract: Pancreatic ductal adenocarcinoma (PDAC) is an aggressive disease, which is characterized by its high in- vasiveness, rapid progression, and profound resistance to therapy. Gemcitabine is the first-line treatment option for pancreatic cancer patients, but the overall survival is quite low. Therefore, it is an urgent issue to identify new mol- ecules for improved therapies, with better efficacy and less toxicity. Our previous data indicated that Euchromatic histone-lysine N-methyltransferase 2 (EHMT2) functions as a therapeutic target to override GEM resistance and promote metastasis in the treatment of pancreatic cancer. Here, we screened a small-molecule library of 143 protein kinase inhibitors, to verify cytotoxicity of different inhibitors in EHMT2-depleted cells. We determined that the EHMT2 plays a promising modulating role for targeted PI3K/mTOR inhibition. Our data revealed that EHMT2 down-regulates p27 expression, and this contributes to tumor growth. The depletion of EHMT2, ectopic expres- sion of methyltransferase-dead EHMT2, or treatment with an EHMT2 inhibitor decreases H3K9 methylation of p27 promoter and induces G1 arrest in PANC-1 pancreatic cancer cells. Consistent with these findings, in vivo tumor xenograft models, primary tumors, and the Oncomine database utilizing bioinformatics approaches, also show a negative correlation between EHMT2 and p27. We further demonstrated that low EHMT2 elevated BEZ235 sensitiv- ity through up-regulation of p27 in PDAC cells; high levels of SKP2 decrease BEZ235 responsiveness in PDAC cells. Altogether, our results suggest the EHMT2-p27 axis as a potential marker to modulate cell response to dual PI3K/ mTOR inhibition, which might provide a strategy in personalized therapeutics for PDAC patients. Keywords: EHMT2, SKP2, p27, pancreatic cancer, cell cycle Introduction peutic agents [3]. Gemcitabine, the standard treatment for advanced pancreatic cancer Pancreatic ductal adenocarcinoma (PDAC) is since 1997, displays modest effects with medi- one of the most aggressive cancer types with a an overall survival times ranging from 5 to 8 five-year survival rate of less than 8% [1]. More months [4, 5]. Combination with tyrosine kinase than 80% of patients were diagnosed with inhibitor, erlotinib, reveals limited but signifi- unresectable or metastatic PDAC due to unno- cant improvement in overall survival [6], and ticed clinical symptoms and insufficient specif- combination chemotherapy with FOLFIRINOX ic examinations [2]. There are dismal results (5-fluorouracil, oxaliplatin, irinotecan, leucovo- from several trials of PDAC, even in novel thera- rin) in metastatic disease shows superior sur- Molecular targeting of EHMT2 in pancreatic ductal adenocarcinoma vival but moderate toxicity [7]. In addition, the sion levels in pancreatic cancer cell line. p27 MPACT study demonstrated improvement of expression in pancreatic cancer is significant overall survival in nearly one year by using nab- because it may be a valuable disease biomark- paclitaxel plus gemcitabine versus gemcitabine er and therapeutic strategy. alone [8]. Materials and methods The human EHMT2 (Euchromatic histone-lysine N-methyltransferase) gene is located at the Cell lines, reagents and plasmids chromosome band 6p21.33. The EHMT2 gene encodes a methyltransferase (EHMT2, also PANC-1 and Mia PaCa-2 cells were cultured in known as G9a) that methylates lysine residues Dulbecco’s modified Eagles medium (DMEM) of histone H3 and functions as recruitment of containing 10% fetal bovine serum (FBS). sh- additional epigenetic regulators and repressors EHMT2 plasmids were from the National RNAi of transcription. Our previous study demon- Core Facility (Academia Sinica, Taiwan). sh- strated that EHMT2 induces down-regulation of EHMT2 #1 sequence: GCTCCAGGAATTTAACAA- histone demethylase KDM7A, which inhibits GAT; sh-EHMT2 #2 sequence: CTCCAGGAATTT- de-methylation of H3K9m2 and H3K27m3 of AA CAAGATT. Antibodies againsy EHMT2, p21, the E-cadherin promoter, inhibiting E-cadherin Tubulin, Actin, PCNA were purchased from expression, and enhancing epithelial-mesen- Genetex (SanAntonio, TX, USA). p27, p57, H3- chymal transition, migration, and invasion [9]. K9m2, H3K4m3, H3K27m3, Ki67 were pur- In addition, EHMT2 mediates interleukin-8 chase from Abcam (Cambridge, MA). UNC0638 expression to elevate gemcitabine resistance was purchased from Cayman Chemical (Ann and trans-endothelial invasion [10]. However, Arbor, MI, USA). Cycloheximide (C4859, CHX, more studies are needed to precisely elucidate 100 μg/ml) was obtained from Sigma. how the multiple properties of EHMT2 contrib- ute to tumorigenesis. Quantitative reverse transcriptional PCR (RT- qPCR) p27, a cell cycle negative regulator, inhibits cyclin-dependent kinase (CDK) complexes to Total RNA extraction was extracted using the cause cell cycle arrest. Overexpression of p27 RNeasy mini kit (qiagen, Valencia, CA), accord- prevents CDK2 activation and entry from the ing to the manufacturer’s instructions. Equal late G1 into the S phase of the cell cycle [11]. In amounts of RNA were used to synthesize first- several types of cancers, the expression of p27 strand cDNA using the RT2 first strand kit represents poor prognosis, including pancreat- (Qiagene). RT-PCR was performed using SYBR ic cancer [12-15]. Some studies reveal that p27 Green on Real-Time PCR System (Applied is regulated via post-translational modifications Biosystems, Foster City, CA). The primers of [16]. SKP2 is a component of the SCF ubiquitin p27 were (forward) 5’-AAGGGCCAACAGAACA- ligase complex, which mediates the degrada- GAAG-3’ and (reverse) 5’-GGATGTCCATTCAAT- tion of p27 [17, 18] and participates in G2-M GGAGTC-3’. p27 promoter chip sequence were progression [19]. Several investigations indi- (forward) 5’-ACTCGCCGTGTCAATCATTT-3’ and cated that p27 expression is lost frequently in (reverse) 5’-AACACCCCGAAAAGACGAG-3’. pancreatic cancer patients [20-24]. Flow cytometry for cell cycle analysis To date, the association between EHMT2 and p27 is still uncertain in pancreatic cancer. In PANC-1 and Mia PaCa-2 cells were transfected our study, we found that the depletion of EHMT2 with sh-EHMT2 and harvested by trypsinization halts the cell cycle at G1 phase by activating and fixed with 70% ice-cold ethanol for over- p27 post-translational modifications. p27 up- night at -20°C. Next day, the cell pellet was re- regulation ceases cancer cell replication and suspended in PI-staining buffer (50 μl/ml PI, proliferation. The inverse relation between EH- RNAse A, Beckman Coulter, Brea, CA) and was MT2 and p27 is established in vivo and in vitro. incubated for 15 min at 37°C for further cell In addition, combination with a dual PI3K/ cycle analysis. Cell cycle distribution was ana- mTOR inhibitor significantly improves the thera- lyzed by FACS Calibur (BD Biosciences, San peutic effect, as evidenced by the p27 expres- Diego, CA) using ModFit software. 1813 Am J Cancer Res 2018;8(9):1812-1822 Molecular targeting of EHMT2 in pancreatic ductal adenocarcinoma Figure 1. Knockdown of EHMT2 leads to the reduction of tumor growth and the accumulation of cells in G1 arrest. A. Top panel, representative images of pancreatic cancer tissue with high or low expression of EHMT2 in SCID mice. Bottom panel, quantitative analysis of tumor size after injection in designated cells at 4 weeks. Statistical compari- sons were evaluated by one-way ANOVA. (*P < 0.05). B. Representative staining of PCNA, EHMT2 in tumors of dif- ferent treatment groups. Original magnification: × 40, scale bar: 10 μm. C. Expression profiles of cell cycle in PANC-1 and PANC-1 EHMT2 deficient (sh-EHMT2) cell lines were analyzed by flow cytometry, and the percentage of the cell population at different stages of the cell cycle were calculated. Cell viability test left hide leg of each 7-wk-old nonobese diabet- ic/servere combined immunodeficient mice. 3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyltetra- After 4 weeks, eight mice of each group were zolium bromide (MTT) assay was used for sacrificed for