Wnt Signaling in IBD-Related Colon Cancer

University Of California Irvine, Irvine CA

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Abstract

DESCRIPTION (provided by applicant): Wnt ligands induce a signaling cascade by binding to cell surface frizzled receptors. This leads to increases in cellular beta-catenin and, ultimately, the induction of transcription of growth promoting genes. This process, mimicked by mutations in the APC gene, is integrally associated with the process of sporadic colon carcinogenesis. Mutations in APC and beta-catenin appear to be rare in inflammatory bowel disease (IBD)-related tumors. However, abnormal expression of other components of the Wnt pathway, including frizzled receptors, SARP1 and disheveled (dvl) have been described. In this proposal, the expression of upstream elements of the Wnt signal transduction pathway, frizzled receptors and frizzled inhibitory molecules will be defined in normal, dysplastic and malignant colonic tissues from patients with IBD. First, we will examine the expression of Fz receptors by immunohistochemistry in IBD-associated colon cancer tissues and compare this expression to adjacent mucosal tissues and sporadic colon cancers. In situ hybridization with anti-sense RNA probes specific for each of the ten Fz receptor subtypes as well as for specific frizzled-inhibitory proteins (FIPs) will then be utilized to define their expression in these tissues. Next, colon biopsies of normal and dysplastic mucosa will be obtained prospectively from patients with IBD undergoing surveillance colonoscopy. These tissues will be evaluated for expression of frizzled receptor subtypes and FIPs and also for activation of Wnt signaling, indicated by nuclearization of beta-catenin and increased expression and activity of a downstream pathway component, LEF1. Finally, the role of specific Fz receptor subtypes in the initiation and propagation of Wnt pathway signals will be defined utilizing a novel, in vitro, co-culture expression system. Those Fz receptor subtypes which exhibit differential expression in IBD tissues will be evaluated in this system. Expression constructs for individual Fz receptor subtypes will be utilized for more in-depth analysis in colon cancer cell lines. The precise effects of FIPs on Wnt signaling will be defined in vitro, with attention to the potentially disparate responses of different, specific, Fz receptor subtypes.