Abstract
Abstract The initiation and progression of colorectal tumorigenesis is characterized by alterations in gene expression that allow for the overexpression of oncogenic and tumor-promoting factors. In normal cells, the mRNA transcripts of these cancer-associated genes are targeted for rapid decay through AU-rich elements (ARE) present in the mRNA 3’ untranslated region (3′UTR). However, growing evidence reveals that the loss of ARE-mediated mRNA decay is a characteristic feature contributing to pathogenic gene expression in colorectal cancer. Our prior work identified enhanced expression of the RNA-binding protein HuR to occur during colon tumorigenesis and HuR overexpression is correlated with poor clinical prognosis. In this capacity, HuR promotes overexpression of many cancer-associated factors by binding to their ARE and interfering with subsequent rapid mRNA decay. To determine the functional significance of HuR overexpression in vivo, a tissue-specific HuR-transgenic mouse (HuR-Tg) was created that overexpresses HuR in the epithelium of the small intestine and colon. HuR-Tg mice displayed normal growth and did not reveal any morphological changes in the gastrointestinal tract. To test if HuR overexpression can impact tumorigenesis downstream a tumor initiating event, crosses between HuR-Tg mice and the APCMin/+ mouse, a genetic model of gastrointestinal tumorigenesis, were performed. As early as 12 weeks of age, HuR-Tg/APCMin/+ lines display a 2- to 4-fold increase in tumor burden and size in both the colon and small intestine compared to APCMin/+control mice. Based on HuR's ability to bind various ARE-containing mRNAs associated with angiogenesis, vascular density was assayed in tissue derived from HuR-Tg/APCMin/+ mice. Micro-vessel density was 2-fold greater in the tumors and surrounding tissue in APCMin/+ mice overexpressing HuR. Angiogenic mRNA array analysis of tumors derived from HuR-Tg/APCMin/+ mice showed enhanced expression of multiple ARE-containing angiogenic genes including the HuR target genes vascular endothelial growth factor (VEGF) and cyclooxygenase-2 (COX-2). Furthermore, dietary treatment of HuR-Tg/APCMin/+ mice with celecoxib attenuated HuR-dependent tumor formation and suppressed micro-vessel density and VEGF expression. These findings indicate that HuR functions during colon tumorigenesis downstream of a tumor-initiating event to stabilize ARE-containing mRNAs associated with tumor vascularization and identify this mRNA stability factor as a new molecular target for therapeutic intervention in controlling angiogenic gene expression. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 3083. doi:10.1158/1538-7445.AM2011-3083
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