The human SRC gene encodes pp60c-Src (or c-Src), a 60 kDa, non-receptor tyrosine kinase frequently activated in colon and other tumors. Many studies have demonstrated c-Src activation can be accounted for by overexpression of c-Src protein, and that this overexpression is important for the fully transformed phenotype of cancer cells. The general goal of this thesis, therefore, was to determine the mechanism of this overexpression in human cancer cells. Examination of c-Src expression and activity in human colon cancer cell lines showed that c-Src activation was due to transcriptional activation of the SRC gene. SRC transcription is directed by the ubiquitous, Sp1 regulated SRC1A promoter, and the HNF-1alpha regulated, tissue restricted SRC1alpha promoter. To study the mechanism of SRC transcriptional activation in human cancer cell lines, a dual SRC promoter reporter construct was generated with both these promoters in their natural, physiologically linked context. Very low activity of the SRC1alpha promoter, relative to SRC1A, was consistently observed from this construct, leading to the conclusion that an enhancer element elevates SRC1alpha promoter activity. Interestingly, the HNF binding site in the SRC1alpha promoter enhanced SRC1A promoter activity in the dual promoter construct, but only in a colon cancer cell line with activated SRC. These results therefore suggest SRC transcriptional activation results from enhancer action and/or SRC promoter cross-talk in subsets of human cancer cells. <p> This study has also determined that histone deacetylase inhibitors (HDIs), compounds with documented anti-neoplastic properties, repress transcription from both SRC promoters in various cancer cell lines. To identify the mechanism of this repression, various deletion and mutant SRC promoter constructs were assayed, but HDI response elements were not identified. However, it was discovered that both promoters shared a common requirement for functional TAF1/TAF(II)250, a component of the general transcription factor TFIID. Compromised TAF1 function impaired SRC transcription, but also blocked SRC repression by HDIs. Experiments with SRC:WAF1 promoter chimeras showed the SRC promoters' TAF1 requirement could be conferred on the heterologous, TAF1-independent promoter for the WAF1 gene, which encodes the cell cycle inhibitor p21. These chimeras were also repressed by HDIs, despite WAF1 normally being strongly induced by these agents. These results therefore provide a potential functional link between promoter architecture, TAF1 dependence, and HDI mediated transcriptional repression.
| Identifer | oai:union.ndltd.org:USASK/oai:usask.ca:etd-08212003-170723 |
| Date | 25 August 2003 |
| Creators | Dehm, Scott Michael |
| Contributors | Laferte, Suzanne, Krone, Patrick H., Davie, James, Bonham, Keith, Roesler, William J., Warrington, Rob C. |
| Publisher | University of Saskatchewan |
| Source Sets | University of Saskatchewan Library |
| Language | English |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://library.usask.ca/theses/available/etd-08212003-170723/ |
| Rights | unrestricted, I hereby certify that, if appropriate, I have obtained and attached hereto a written permission statement from the owner(s) of each third party copyrighted matter to be included in my thesis, dissertation, or project report, allowing distribution as specified below. I certify that the version I submitted is the same as that approved by my advisory committee. I hereby grant to University of Saskatchewan or its agents the non-exclusive license to archive and make accessible, under the conditions specified below, my thesis, dissertation, or project report in whole or in part in all forms of media, now or hereafter known. I retain all other ownership rights to the copyright of the thesis, dissertation or project report. I also retain the right to use in future works (such as articles or books) all or part of this thesis, dissertation, or project report. |
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