The studies presented in this dissertation establish the dynamics of Eleven nineteen Lysine-rich leukemia (ELL) family of elongation factors during B cell differentiation and provide a description of ELL3 function in B cells.
The transition from a mature naïve B cells into an activated B cell is dependent on a large increase in transcriptional output, which is followed by focused expression on secreted immunoglobulin upon terminal differentiation into plasma cell. While ELL family members have previously been implicated in alternative splicing at the immunoglobulin heavy chain locus in plasma cells, their presence and function prior to differentiation is currently not known. However, the use of elongation factors has been implied by the finding of mostly paused RNA polymerase II in the genome of naïve B cells.
In the first study, the expression of transcriptional elongation factor ELL3 is shown to be restricted to activated B cells and B cell lymphomas. All three family members were characterized in B cell lymphoma cell lines, genome wide expression, microarray analysis and primary B cell stimulus. The expression of ELL3 was induced upon activation of B cells concurrently with family member ELL. In addition, the abundant expression of ELL3 was restricted to GC derived B cell lymphoma cell lines. While the expression of ELL is maintained, the expression of ELL3 is diminished and ELL2 is up-regulated in terminally differentiated plasma cells.
The expression of master regulator of terminal plasma cell differentiation PRDM1 was inverse correlated with that of ELL3. To further establish PRDM1s role in regulating the ELL family member dynamics, global binding was assessed in plasma cell lines. Chromatin immunoprecipitation followed by quantitative PCR was utilized to identify direct association of PRDM1 at exclusively the ELL3 loci. Ectopic expression of PRDM1 in B cells down regulated the expression of ELL3. Furthermore, two consensus PRDM1 binding sites were defined at the ELL3 loci, which mediate significant repression of the promoter activity. Collectively, these experiments indicate that PRDM1 mediates the switch from ELL3 in B cells to ELL2 in plasma cells.
The data presented in the final chapter aimed at defining a function for ELL3 in the cells that express it most abundantly, which are B cell lymphoma cell lines. Transient depletion of ELL3 in a Burkitt’s lymphoma cell line resulted in a diminished proliferation rate due to a severe disruption of DNA replication and its regulators minichromosome maintenance proteins. Additionally, compromised cell division and mitotic regulators were observed along with increased DNA damage and cell death.
The data presented here demonstrate a key role for ELL3 in the proliferation and survival of B cell lymphomas and positions ELL3 as an attractive therapeutic target against B cell lymphoma’s with a germinal center origin.
| Identifer | oai:union.ndltd.org:USF/oai:scholarcommons.usf.edu:etd-8316 |
| Date | 09 January 2018 |
| Creators | Alexander, Lou-Ella M.m. |
| Publisher | Scholar Commons |
| Source Sets | University of South Flordia |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | Graduate Theses and Dissertations |
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