Date of Graduation

2016

Document Type

Thesis

Degree Type

MS

College

Eberly College of Arts and Sciences

Department

Biology

Committee Chair

Shuo Wei

Committee Co-Chair

Ashok Bidwai

Committee Member

Clifton Bishop

Abstract

Throughout development, canonical Wnt signaling contributes to the formation and maintenance of a wide array of cells, tissues, and organs. Dys-regulated Wnt signaling during embryonic development is implicated in developmental defects known as neurochristopathies, including craniofacial and heart defects, as well as defects in neural development. Due to its roles in stem cell maintenance and self-renewal, tissue homeostasis, and regeneration, aberrant Wnt signaling in adult tissues can result in various forms of cancer, including colorectal cancer, breast cancer, lung cancer, and gastro-intestinal cancer, among others. Dys-regulated Wnt signaling is also implicated in other pathologies including bone disease, and metabolic diseases, such as Type II diabetes. Our lab has previously identified a novel crosstalk between canonical Wnt signaling and ephrin signaling. Ephrin signaling occurs through the interaction of ephrin ligands and Eph receptor tyrosine kinases, and is bidirectional. Due to the roles of ephrin signaling in tissue development and maintenance, aberrant ephrin signaling is implicated in many diseases including bone remodeling diseases, diabetes, and cancer. The molecular mechanism of the crosstalk between canonical Wnt signaling and ephrin-B signaling remains unknown. beta-catenin is a key intracellular effector of canonical Wnt signaling that transduces the signal to the nucleus, where beta-catenin interacts with the TCF/LEF transcription factors and activates transcription of target genes. Due to its central role in transducing the canonical Wnt signal to the nucleus, we predict that ephrin-B signaling antagonizes canonical Wnt signaling by affecting the stability and/or sub-cellular localization of beta-catenin, or the interaction between beta-catenin and TCF/LEF transcription factors. By employing mouse ephrin-B constructs in human cell lines, we show that the canonical Wnt - ephrin-B crosstalk is conserved between frogs and mammals. We also found that ephrin-B antagonism of canonical Wnt signaling is likely independent of ubiquitin proteasome system (UPS)-mediated degradation of beta-catenin. Furthermore, confocal immunofluorescence microscopy revealed that overexpression of ephrin-B in HEK293T cells treated with lithium chloride (LiCl) seems to promote membrane localization of beta-catenin, particularly at the apical Z sections. These results suggests that re-localization of beta-catenin to the cell membrane may contribute to the ephrin-B antagonism of canonical Wnt signaling.

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