| Summary: | PPP2R2A is a regulatory subunit of protein phosphatase 2A (PP2A). Genomic analysis based on 2000 breast cancer cases identified PPP2R2A as one of the deletion hotspots in breast cancer genomes and 63% of PPP2R2A deletions were found in estrogen receptor positive (ER+) breast cancers. We hypothesized that the high frequency deletion of PPP2R2A, as well as its correlation with ER expression status, implies its functional roles in breast cancer development. In this thesis, I investigated the functional impacts of PPP2R2A deletion in breast cancer development from the aspects of ER signaling, PP2A complex composition, and cell morphological changes. First, I studied ER signaling activity and mechanism in T47D cells with the analysis of transcriptome, ER binding specificity and ER co-factor recruitment, etc. Second, I studied PP2A complex composition in three breast cell models with targeted quantitative mass spectrometry (MRM). Last, I studied morphological changes in mammary breast cell models, 184-hTERT and MCF10A, in terms of cell proliferation, surface protein localization, and cell mobility based on transcriptome and signaling network analysis. As a result, reduced expression of PPP2R2A led to differential expression of ER response genes, alterations in ER binding specificity, and changes in ER co-factor composition. SPDEF was particularly up regulated and recruited in ER transcriptional machinery. Analysis in clinical samples also confirmed the correlation of SPDEF up regulation with ER expression status and PPP2R2A copy number loss. In addition, MRM analysis revealed changes in PP2A complex composition after PPP2R2A knockdown with increased relative abundance of STRN in PP2A complexes in ER positive cell models. Finally, my morphological studies demonstrated mislocalization of cell surface proteins and enhanced cell mobility in breast mammary epithelial cell models with reduced PPP2R2A expression. In conclusion, PPP2R2A plays an important role in regulating cell signaling activity and cellular morphology and its genomic deletion would significantly contribute to the development of breast cancer. === Medicine, Faculty of === Pathology and Laboratory Medicine, Department of === Graduate
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