Date of Award

2017

Document Type

Thesis - MUSC Only

Degree Name

Master of Biomedical Science

Department

Pathology and Laboratory Medicine

College

College of Graduate Studies

First Advisor

Steven Carroll

Second Advisor

Alan Diehl

Third Advisor

Victoria Findlay

Fourth Advisor

Qi Wang

Fifth Advisor

Dennis Watson

Abstract

For many years, the receptor tyrosine kinase ErbB3/HER3, a member of the EGFR family, was thought to be “kinase dead” and thus unlikely to be an oncogene. This paradigm shifted when ErbB3 was found to possess weak intrinsic kinase activity along with the discovery of ErbB3 somatic mutations being discovered in several human cancers. These data and other observations have now implicated ErbB3 in the progression and maintenance of many human cancers. ErbB3 action in these cancers is likely dependent on its ability to modulate essential downstream signaling pathways. In keeping with this expectation, plasma membrane-associated ErbB3 has been shown to activate canonical cytoplasmic signaling pathways that drive the pathogenesis of many cancers (e.g., the PI3 kinase-Akt-mTOR pathway). However, it is highly likely that other important ErbB3-modulated signaling molecules have not yet been discovered. These unknown proteins may mediate ErbB3 action at the plasma membrane. Alternatively, they may function at other sites of ErbB3 expression such as intracellular membranous compartments or the nucleus. Our laboratory used a split-ubiquitin yeast two-hybrid screen to identify 10 novel proteins that potentially interact with the ErbB3 receptor. These proteins have all been previously implicated in protein trafficking or nuclear functions. To examine ErbB3 function in intracellular membranous compartments, I focused on Reep5, a candidate ErbB3-interacting protein that resides within the endoplasmic reticulum. Co-immunoprecipitation experiments demonstrated that Reep5 interacts with ErbB3 in non-transformed MCF10A breast cells and in transformed MCF-7 breast cancer cells. Multi-label immunofluorescence microscopy showed that ErbB3 and Reep5 co-localize in subcellular compartments, albeit, with differential staining patterns. Knockdown of Reep5 expression with short hairpin RNAs significantly increased the proliferation of MCF10A cells. Surprisingly, Reep5 knock-down did not affect the proliferation of MCF-7 cells. Surprisingly, Reep5 knock-down also caused a significant increase in ErbB3 nuclear staining in the MCF10A cells, indicating that a loss of Reep5 expression altered the trafficking of ErbB3 protein. These observations suggest that the ErbB3-Reep5 interaction plays an important role in directing ErbB3 protein to distinct cellular compartments. Elucidating the biological role of this interaction may provide a biomarker and/or a therapeutic target for ErbB driven cancers.

Rights

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