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THE ROLE OF THE BAXΔ2 C-TERMINAL STRUCTURE IN CASPASE-8- MEDIATED CELL DEATH OF HUMAN COLORECTAL CARCINOMA CELLS
Title
THE ROLE OF THE BAXΔ2 C-TERMINAL STRUCTURE IN CASPASE-8- MEDIATED CELL DEATH OF HUMAN COLORECTAL CARCINOMA CELLS
Creator
Nelson, Adam
Date
2018, 2018-05
Description
BaxΔ2 is an isoform of the proapoptotic Bcl-2 family member Bax that promotes cell death via caspase-8 activation. The C-terminus of BaxΔ2 has...
Show moreBaxΔ2 is an isoform of the proapoptotic Bcl-2 family member Bax that promotes cell death via caspase-8 activation. The C-terminus of BaxΔ2 has been shown to be crucial for caspase-8 dependent cell death in colon cancer cells. However, it is unknown whether the C-terminal primary sequence or secondary structure is necessary for interaction with caspase-8. In this project, several BaxΔ2 C-terminal mutants were generated based on secondary structure predictions. Models showed that mutating Leu164 and Thr165 to Ala (LT-AA) would increase the probability of alpha helix formation, while mutating Leu164 to Pro (L-P) would decrease the probability of alpha helix formation. Expression of these mutant proteins in colon cancer HCT116 cells, showed that L164P, and not L164A/T165A, significantly impaired BaxΔ2 function. The mutant L164P proteins formed atypical aggregates, and their ability to induce cell death was also significantly decreased when compared to the wild type. These results indicate that the BaxΔ2 C-terminal tridimensional structure, and not the specific primary sequence, is critical for triggering aggregation-mediated cell death.
M.S. in Biology, May 2018
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IDENTIFICATION OF BAX∆2 FRAMESHIFTING REGION VIA DUAL LUCIFERASE ANALYSIS
Title
IDENTIFICATION OF BAX∆2 FRAMESHIFTING REGION VIA DUAL LUCIFERASE ANALYSIS
Creator
Reiner, Katherine
Date
2020
Description
The antitumor protein Bax is susceptible to microsatellite instability (MSI) mutations that alter its open reading frame by changing Baxs’...
Show moreThe antitumor protein Bax is susceptible to microsatellite instability (MSI) mutations that alter its open reading frame by changing Baxs’ microsatellite of eight guanines (G8) to seven guanines (G7). This mutation results in a frameshift that is corrected by alternative splicing, making Bax∆2. Evidence shows that non-MSI mutated full length Bax∆2 (Bax∆2 G8) can be found in tissue. However, the extra guanine in Bax∆2 should result in premature termination of protein synthesis. Therefore, we believe that Bax∆2 is capable of +1 frameshifting to correct the out of frame sequence caused by splicing. The dual luciferase assay system is a useful tool for measuring frameshifting and in this study, we cloned full length Bax∆2 G8 into a dual luciferase vector to analyze frameshifting. Using this method, we found that the full length Bax∆2 G8 sequence has 3.5% frameshifting activity. To further determine whether the frameshifting occurs in or near the G8 microsatellite, we focused on several truncated constructs containing the first three exons. The results from dual luciferase assay showed that frameshifting activity was high in the constructs containing the G8 microsatellite but diminished when the G8 microsatellite region was removed. Surprisingly, constructs containing exon 4 and 5, which are away from the predicted frameshifting region, also showed frameshifting activity. One possibility to explain these results is that mRNA structures, which are critical to frameshifting, could be altered by construct truncation and consequently lead to artificial frameshifting. Thus, using truncated constructs may not be a viable option for testing frameshifting activity. To maintain mRNA integrity, point mutations within the full sequence, could be a better option to identify the frameshifting site.
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