Molecular and Cellular Pathobiology Prohibitin Attenuates Colitis-Associated Tumorigenesis in Mice by Modulating p53 and STAT3 Apoptotic Responses

Although inflammatory bowel disease is associatedwith higher risk of colorectal cancer, the precise pathogenic mechanisms underlying this association are not completely understood. Prohibitin 1 (PHB), a protein implicated in the regulation of proliferation, apoptosis, and transcription, is decreased in intestinal inflammation. In this study, we have established a key function for PHB in mediating colitis-associated cancer. Wild-type and transgenic (Tg) mice specifically overexpressing PHB in intestinal epithelial cells were subjected to a classical two-stage protocol of colitis-associated carcinogenesis. In addition, wild-type and p53 null human cell models were used to assess PHB interaction with STAT3 and p53. Wild-type mice exhibited decreased mucosal PHB protein expression during colitis-associated carcinogenesis. Tg mice exhibited decreased susceptibility in a manner associated with increased apoptosis, p53, Bax, and Bad expression plus decreased Bcl-xL and Bcl-2 expression. PHB overexpression in wild-type but not p53 null human cells increased expression of Bax, Bad, and caspase-3 cleavage. In wild-type p53 cells, PHB overexpression decreased basal and interleukin-6-induced STAT3 activation and expression of the STAT3 responsive genes Bcl-xL and Bcl-2. PHB coimmunoprecipitated with phospho-STAT3 in addition to p53 in cultured cell lysates and colon mucosa. This is the first study to show interaction between PHB and STAT3 in vivo. In summary, our findings suggest that PHB protects against colitisassociated cancer by modulating p53and STAT3-mediated apoptosis. Modulation of PHB expression in intestinal epithelial cells may offer a potential therapeutic approach to prevent colitis-associated carcinogenesis. Cancer Res; 72(22); 5778–89. 2012 AACR. Introduction Inflammatory bowel disease (IBD) includes 2 major chronic intestinal disorders, Crohn's disease and ulcerative colitis (UC), which share related characteristics such as mucosal damage and diarrhea but have distinguishing clinical features. Evidence suggests that in addition to thewidely accepted aberrant mucosal immune response, nonimmune cells including epithelial cells play an emerging role in the pathogenesis of disease by modulating mucosal barrier integrity and homeostasis (1). An association between IBD and colorectal cancer (CRC) has beenwell establishedwith a cumulative risk of developing CRC of 7% after 20 years for UC and 8% for Crohn's disease (2). Previous studies have shown that production of proinflammatory cytokines in the lamina propria contribute to tumor growth and cancer development during intestinal inflammation (3, 4). Prohibitin 1 (PHB) is an evolutionarily conserved, multifunctional 32 kDa protein implicated in cellular processes including the regulation of cell cycle progression, apoptosis, and transcription (5–7). Expression of PHB is decreased in mucosal biopsies from UC and Crohn's disease afflicted patients and in the dextran sodium sulfate (DSS) and interleukin (IL)-10 / mouse models of colitis (8, 9). Proinflammatory cytokines such as TNFa and reactive oxygen species decrease expression of intestinal epithelial PHB in vivo and in vitro (8–10). Restoration of colonic epithelial PHB expression using genetic manipulation [villin-PHB transgenic (Tg) mice] or therapeutic delivery to the colon via nanoparticles or adenovirus protected mice from experimental colitis (11, 12). The role of PHB in cancer cell proliferation and/or tumor suppression remains controversial especially because PHB expression is increased in many transformed cells and tumors (13–19). Consensus binding sites for the oncoprotein Myc are present in the PHB promoter and likely contribute to the increased PHB levels in many tumors (20). Although somatic mutations in the PHB gene were observed in a few sporadic breast cancers, none were identified in the ovary, hepatic, or Authors' Affiliations: Department of Internal Medicine, Division of Gastroenterology, Baylor Research Institute, Baylor UniversityMedical Center; Department of Medicine, Veterans Affairs North Texas Health Care System, University of Texas Southwestern Medical Center, Dallas, Texas; and Gastroenterology Division, Department of Medicine and Department of Oncology, the Sidney Kimmel Comprehensive Cancer Center and the Johns Hopkins School of Medicine, Baltimore, Maryland Note: Supplementary data for this article are available at Cancer Research Online (http://cancerres.aacrjournals.org/). Corresponding Author: Arianne L. Theiss, Division of Gastroenterology, 250 Hoblitzelle, Baylor Research Institute, Baylor University Medical Center, Dallas, TX 75246. Phone: 214-820-2752; Fax: 214-818-9292; E-mail: [email protected] doi: 10.1158/0008-5472.CAN-12-0603 2012 American Association for Cancer Research. Cancer Research Cancer Res; 72(22) November 15, 2012 5778 on May 28, 2017. © 2012 American Association for Cancer Research. cancerres.aacrjournals.org Downloaded from Published OnlineFirst August 6, 2012; DOI: 10.1158/0008-5472.CAN-12-0603