Human Cancer Biology Putative Tumor-Suppressive Function of Krüppel-Like Factor 4 in Primary Lung Carcinoma

Purpose:Krüppel-like factor 4 (KLF4) is a zinc-fingerprotein that plays important roles in stem cellsandthedevelopmentofgastriccancers.However, theroleofKLF4 inprimary lungcancer is unknown. The purpose of this study is to determine possible roles of KLF4 in lung cancer. Experimental Design: The KLF4 expression in primary lung cancer tissues and casematched normal lung tissueswere determinedbyprotein andmRNAanalyses. The effects of KLF4 on cell proliferation, clonogenic formation, and cell cycle progression were determined in cultured lung cancer cells or bronchial epithelial cells after enforced KLF4 overexpressionor small interferingRNAknockdown. The in vivoantitumor activity ofKLF4was evaluatedbyusing stably transfected lungcancer cells andbyadenovector-mediatedgene delivery. The effect of KLF4 in regulating p21 and cyclin D1 was also evaluated. Results: KLF4 protein and mRNA levels were dramatically decreased in most primary lung tumors compared with in case-matched normal lung tissues. Enforced expression of KLF4 resulted in marked inhibition of cell growth and clonogenic formation. The tumor-suppressive effect of KLF4 was associated with its role in up-regulating p21 and down-regulating cyclinD1, leading to cell cycle arrest at theG1-S checkpoint. Knockdown of KLF4 promoted cell growth in immortalized human bronchial epithelial cells. The enforced expression of KLF4 gene to lung cancer cells by ex vivo transfection or adenovector-mediated gene transfer suppressed tumor growth in vivo. Conclusions: Our results suggest that KLF4 plays an important role in suppressing the growth of lung carcinoma. (Clin Cancer Res 2009;15(18):5688–95) The human Krüppel-like factor (KLF) family of transcriptional factors has at least 25 members, all of which contain three domains of Krüppel-like zinc fingers. They regulate a variety of target genes that are involved in differentiation, proliferation, and apoptosis (1).Their roles in oncogenesis and tumor progression have also recently been recognized. KLF4 (formerly GKLF) is a KLF protein that has been reported to activate or repress genes that are involved in cell cycle regulation and differentiation (2, 3). KLF4 expression is frequently lost in various human cancer types, such as colorectal cancer (4), gastric cancer (5), esophageal squamous cell carcinoma (6), intestinal cancer (7), prostate cancer (8), and bladder cancer (9). Recently, KLF4 was shown to undergo promoter methylation and loss of heterozygosity in gastrointestinal cancer (4, 5). Consistent with its tumor-suppressive function, the overexpression of KLF4 reduces the tumorigenicity of colonic and gastric cancer cells in vivo (5, 10). These observations indicate that KLF4 acts as a tumor suppressor. However, high KLF4 expression has been found in primary breast ductal carcinoma (11) and oral squamous cell carcinoma (12). It was also reported that ectopic KLF4 expression in mice induced squamous epithelial dysplasia (13). Thus, KLF4 may function as either a tumor suppressor or an oncogene in tissue type–dependent or cell context–dependent manners. More recently, KLF4 was reported to play important roles in stem cells (14, 15). Nevertheless, it remains unknown how KLF4 functions in the development and progression of lung cancer. The important roles of KLF4 in stem cells and various cancers prompted us to investigate the level of KLF4 expression in human lung cancer tissues and the effects of its alteration. We found that KLF4 expression was substantially decreased in human lung cancer. Consistently, restoration of or an increase Authors' Affiliations: Sir Run Run Shaw Hospital, Zhejiang University, Key Laboratory of Biotherapy of Zhejiang Province, Hangzhou, People's Republic of China and Departments of Thoracic and Cardiovascular Surgery and Gastrointestinal Medical Oncology, The University of Texas M. D. Anderson Cancer Center, Houston, Texas Received2/6/09; revised5/28/09; accepted 6/12/09; publishedOnlineFirst 9/8/09. Grant support: National Cancer Institute grant 5R01CA092487-05 (B. Fang), Lung Specialized Program of Research Excellence Developmental Award 5P50CA070907-100007 (S.G. Swisher), NIH core grant 3P30CA01667232S3 (Mendelsohn), Lockton grant-matching funds, Homer Flower Gene Therapy Research Fund, Charles Rogers Gene Therapy Fund, Flora & Stuart Mason Lung Cancer Research Fund, Charles B. Swank Memorial Fund for Esophageal Cancer Research, George O. Sweeney Fund for Esophageal Cancer Research, Phalan Thoracic Gene Therapy Fund, and M.W. Elkins Endowed Fund for Thoracic Surgical Oncology. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked advertisement in accordance with 18 U.S.C. Section 1734 solely to indicate this fact. Note: S.G. Swisher and B. Fang contributed equally. Requests for reprints: Bingliang Fang, Department of Thoracic and Cardiovascular Surgery, Unit 445, The University of Texas M. D. Anderson Cancer Center, 1515 Holcombe Boulevard, Houston, TX 77030. Phone: 713-5639147; Fax: 713-794-4901; E-mail: [email protected]. F 2009 American Association for Cancer Research. doi:10.1158/1078-0432.CCR-09-0310 5688 Clin Cancer Res 2009;15(18) September 15, 2009 www.aacrjournals.org Research. on April 14, 2017. © 2009 American Association for Cancer clincancerres.aacrjournals.org Downloaded from Published OnlineFirst September 8, 2009; DOI: 10.1158/1078-0432.CCR-09-0310