Abstract 4912: The role of long-range enhancer blocker CTCF in TGF-β/β-2 spectrin signaling: A human cancer stem cell disorder, Beckwith-Wiedemann syndrome

Abstract

Abstract Hereditary cancer syndromes provide powerful insights into dysfunctional signaling pathways that lead to sporadic cancers. Beckwith-Wiedemann syndrome (BWS) is a hereditary human cancer stem cell syndrome currently linked to deregulated imprinting at chromosome 11p15 and uniparental disomy (UPD) and is characterized by overgrowth and is associated with an 800-fold increased risk of embryonal neoplasms of childhood that include Wilms’ tumors, hepatoblastomas, pancreatoblastoma, neuroblastoma, rhabdomyosarcoma, and adrenocortical carcinomas. The transcriptional insulator CTCF (CCCTC-binding factor), a highly conserved zinc finger protein, has been implicated in BWS and has diverse regulatory functions, including transcriptional activation/repression, insulation, imprinting, and X chromosome inactivation However, causal molecular defects and genetic models have remained elusive to date in the majority of cases. TGF-β employs Smad proteins as intracellular mediators of signaling to regulate the target gene expression by activating or repressing gene transcription. The non-pleckstrin homology (PH) domain β-general-spectrin (β2SP), a scaffolding protein, functions as a potent TGF-β signaling Smad3/4 adaptor in tumor suppression and development. Yet, the role of the β2SP/TGF-β pathway in human tumor syndromes remains unclear, Our previous data have shown that β2SP is an important effector of TGF-β tumor suppressor function. Deletion of β2SP results in a dramatic and spontaneous formation of liver, gastrointestinal (GI) and pancreatic cancers. Aims: In this study, we investigated the relationship between epigenetic silencing of β-2 Spectrin/TGF-β[[Unsupported Character - ]] Signaling and loss of CTCF protein stabilization in a Human Cancer Stem Cell Disorder: Beckwith-Wiedemann Syndrome. Results show that: 1) β2SP is silenced at its promoter by DNA Methylation in human BWS non-tumor tissues and cell lines. 2) Loss of β2SP, mis-localization of Smad3 and disruption of TGF-β signaling are observed in human Beckwith-Wiedemann non-tumor tissues and cell lines 3) Ectopic expression of β2SP in human BWS cells rescues Smad3 localization and TGF-β target gene activation 4) Increased IGF2 expression in β2SP+/− and β2SP+/−/Smad3+/− mice is similar to that observed in human BWS. 5) CTCF protein levels are markedly decreased in β2SP+/− and β2SP+/−/Smad3+/− tissues. Conclusions: Our results suggest that epigenetic regulation of the TGF-β pathway results in the loss of β2SP and its crucial Smad3 adaptor function. The loss of an adaptor protein β2SP affecting CTCF stabilization, is causally related to the genesis and progression of human BWS. In addition, β2SP+/− and β2SP+/−/Smad3+/− mice provide an important animal model to study BWS. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 4912.