ASXL3 Is a Novel Pluripotency Factor in Human Respiratory Epithelial Cells and A
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Author Manuscript Published OnlineFirst on September 21, 2017; DOI: 10.1158/0008-5472.CAN-17-0570 Author manuscripts have been peer reviewed and accepted for publication but have not yet been edited. ASXL3 is a Novel Pluripotency Factor in Human Respiratory Epithelial Cells and a Potential Therapeutic Target in Small Cell Lung Cancer Vivek Shukla1, Mahadev Rao1, Hongen Zhang2, Jeanette Beers3, Darawalee Wangsa2, Danny Wangsa2, Floryne O. Buishand2, Yonghong Wang2, Zhiya Yu5, Holly S. Stevenson2, Emily S. Reardon1, Kaitlin C. McLoughlin1, Andrew S. Kaufman1, Eden C. Payabyab1, Julie A. Hong1, Mary Zhang1, Sean Davis2, Daniel Edelman2, Guokai Chen3*, Markku M. Miettinen4, Nicholas P. Restifo5, Thomas Ried2, Paul A. Meltzer2, David S. Schrump1# 1Thoracic Epigenetics Section, Thoracic and Gastrointestinal Oncology Branch; 2Genetics Branch, 4Laboratory of Pathology, 5Surgery Branch, Center for Cancer Research, National Cancer Institute; 3NHLBI iPSC Core, National Institutes of Health, Bethesda, MD * Present address: University of Macau, China. Running Title: ASXL3, Lu-iPSC and SCLC Keywords: iPSC, ASXL3, lung cancer, small cell lung cancer, epigenetics Financial Support: This work was supported by NCI Intramural grants ZIA BC 011122 (to D.S. Schrump) and ZIA BC 011418 (to D.S. Schrump), and the Stephen J. Solarz Memorial Fund (to D.S. Schrump). #Corresponding Author David S. Schrump, MD, MBA, FACS Thoracic and GI Oncology Branch, CCR/NCI Building 10; 4-3942, 10 Center Drive, MSC 1201 Bethesda, MD 20892-1201 Tel: 301-496-2128 Fax: 301-451-6934 Email: [email protected] 1 Downloaded from cancerres.aacrjournals.org on September 29, 2021. © 2017 American Association for Cancer Research. Author Manuscript Published OnlineFirst on September 21, 2017; DOI: 10.1158/0008-5472.CAN-17-0570 Author manuscripts have been peer reviewed and accepted for publication but have not yet been edited. Abstract In this study, we generated induced pluripotent stem cells (iPSC) from normal human small airway epithelial cells (SAEC) to investigate epigenetic mechanisms of stemness and pluripotency in lung cancers. We documented key hallmarks of reprogramming in lung iPSC (Lu-iPSC) that coincided with modulation of more than 15,000 genes relative to parental SAEC. Of particular novelty, we identified the PRC2-associated protein, ASXL3 which was markedly upregulated in Lu-iPSC and small cell lung cancer (SCLC) lines and clinical specimens. ASXL3 overexpression correlated with increased genomic copy number in SCLC lines. ASXL3 silencing inhibited proliferation, clonogenicity and teratoma formation by Lu-iPSC, and diminished clonogenicity and malignant growth of SCLC cells in-vivo. Collectively, our studies validate the utility of the Lu-iPSC model for elucidating epigenetic mechanisms contributing to pulmonary carcinogenesis, and highlight ASXL3 as a novel candidate target for SCLC therapy. 2 Downloaded from cancerres.aacrjournals.org on September 29, 2021. © 2017 American Association for Cancer Research. Author Manuscript Published OnlineFirst on September 21, 2017; DOI: 10.1158/0008-5472.CAN-17-0570 Author manuscripts have been peer reviewed and accepted for publication but have not yet been edited. Introduction Lung cancer is the leading cause of cancer-related mortality worldwide, and presently accounts for ~160,000 deaths annually in the United States (1). Approximately 85% of pulmonary carcinomas are non-small cell lung cancers (NSCLC) comprised primarily of adeno-, squamous cell and large cell undifferentiated carcinomas with distinct histologic and molecular features (2). The remaining 15% are small cell lung cancers (SCLC) which exhibit varying degrees of neuroendocrine differentiation, and are typically widely metastatic at presentation with a high propensity for recurrence despite initial, often dramatic responses to chemotherapy (3). Whereas CT screening, targeted therapies, and immune checkpoint inhibitors have recently improved outcomes for some NSCLC patients (1), there have been no advances in detection or treatment of SCLC in over 30 years (3). As such, SCLC has been designated a NCI priority (http://www.lungcanceralliance.org/News/SCLC%20Congressional%20Response%206-30- 14%20FINAL%20with%20appendices.pdf). Although lung cancers may occasionally arise in never-smokers, cigarette smoking remains the predominant risk factor for NSCLC (4); virtually all SCLC arise in active or former smokers with substantial tobacco exposure (3). Despite extensive studies, the genetic and epigenetic mechanisms by which cigarette smoke mediates initiation and progression of lung cancers have not been fully elucidated (5). Previously, we have demonstrated that cigarette smoke condensate (CSC) mediates time and dose dependent epigenomic alterations in normal respiratory epithelial cells (NREC) including perturbations of the histone code, activation of oncomirs and cancer-germline genes, and epigenetic repression of tumor suppressor genes and microRNAs (6-8). These tobacco-induced alterations in NREC mirror those observed in lung cancer cells and primary tumors (9). A central theme emerging from these studies is that via 3 Downloaded from cancerres.aacrjournals.org on September 29, 2021. © 2017 American Association for Cancer Research. Author Manuscript Published OnlineFirst on September 21, 2017; DOI: 10.1158/0008-5472.CAN-17-0570 Author manuscripts have been peer reviewed and accepted for publication but have not yet been edited. complementary mechanisms including DNA methylation, polycomb repressive complexes (PRC) and noncoding RNAs, cigarette smoke induces stem-like phenotypes that coincide with progression to malignancy in NREC, as well as enhanced growth and metastatic potential of lung cancer cells (6-8, 10-12). Reprogramming of somatic cells into induced pluripotent stem cells (iPSC) by induction of a defined set of transcriptional factors has opened a new era in regenerative medicine and cancer biology (13-15). iPSC exhibit numerous similarities to embryonic stem cells (ESCs) including morphology, gene expression profiles, in-vitro proliferation, and in-vivo teratoma formation (13, 16). As such, iPSC have emerged as important models with which to study epigenetic mechanisms contributing to pluripotency in normal cells, as well as stemness, chemo- resistance and metastatic phenotypes of cancer cells (17). In an effort to further delineate epigenetic mechanisms contributing to the pathogenesis of lung cancers and possibly identify novel targets for lung cancer therapy, we sought to develop an iPSC model that might reflect epigenetic transitions from normal to malignant respiratory epithelia. Herein we describe reprogramming of normal human respiratory epithelial cells to pluripotency, and demonstrate that Additional Sex Combs Like-3 (ASXL3) is a novel factor critical for maintenance of pluripotent respiratory epithelial cells, and a potential therapeutic target in SCLC. Materials and Methods Cell Lines: All lung cancer lines were available in repositories at the NCI, or were purchased from ATCC, and cultured as recommended. cdk-4/h-TERT immortalized human bronchial epithelial cells (HBEC) were a generous gift from John Minna (UT-Southwestern, Dallas, TX), 4 Downloaded from cancerres.aacrjournals.org on September 29, 2021. © 2017 American Association for Cancer Research. Author Manuscript Published OnlineFirst on September 21, 2017; DOI: 10.1158/0008-5472.CAN-17-0570 Author manuscripts have been peer reviewed and accepted for publication but have not yet been edited. and were cultured as described (8). Cell lines were tested for mycoplasma regularly (tested the latest in July, 2017) using a kit from Sigma (Cat. no. MP0025), and were validated by HLA typing relative to original stocks. Primary cell culture: Normal human bronchial epithelial cells (NHBE), as well as SAEC derived from a fifty-seven year old Hispanic female non-smoker were purchased from Lonza, and cultured as recommended by the vendor. STEMCCA kit (Millipore, Cat. no. SCR545) was purchased from Millipore, and used as instructed. Irradiated mouse embryonic fibroblasts (MEFs) were obtained from NHLBI core facility, and Matrigel plates (Cat. no. 354230) were purchased from BD Biosciences. Normal foreskin fibroblast (CCD-1079Sk, ATCC Cat. no. CRL-2097) and induced pluripotent cells (ND1.2) derived from foreskin fibroblasts were obtained from the NHLBI core facility, and were grown in DMEM medium and stem cell medium, respectively. 8TM medium (Life technologies; Cat. no. A1517001) and Rho-associated kinase (Rock) inhibitor (Y-27632; Tocris; Cat. no. 1254) were used to culture the stem cells. Generation of iPSCs from SAECs: The STEMCCA vector (Supplementary Figure S1A) and protocol described by Beers at al. (18) were used to reprogram SAEC to pluripotency. Briefly, 2.5 x105 SAEC were plated in each well of a 6-well plate. Once the cells were approximately 70% confluent, they were transduced with STEMCCA lentivirus using polybrene and left to incubate overnight. The transduced cells were then maintained in reprogramming medium with medium changed on alternate days. Six days after transduction, the cells were trypsinized and replated on irradiated mouse embryonic fibroblasts (MEFs; feeder cells). From this day forward, the cells were maintained in reprogramming medium supplemented with basic fibroblast growth 5 Downloaded from cancerres.aacrjournals.org on September 29, 2021. © 2017 American Association for Cancer Research. Author Manuscript Published OnlineFirst on September 21, 2017; DOI: 10.1158/0008-5472.CAN-17-0570