Expression and regulation of O-GlcNAc transferase in tumor cells responding to DNA damage
| Autor: | Yen-Po Feng, 馮彥博 |
|---|---|
| Rok vydání: | 2014 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 103 O-GlcNAcylation, one of the post-translational modifications of proteins, participates in diverse cellular mechanisms. Abnormal cellular O-GlcNAc levels may result in diseases such as diabetes and cancer. It is known that O-GlcNAc transferase (OGT) and O-GlcNAcase (OGA) play important roles in maintaining cellular O-GlcNAcylation homeostasis. OGT catalyzes O-linked glycosylation of proteins by transferring the monosaccharide, N-acetylglucosamine, onto hydroxyl groups of serine/threonine residues, while OGA reverses this modification. OGT has been shown to be associated with chemotherapy resistance in breast cancer cells; cells with OGT deficiency are more sensitive to Tamoxifen-induced cell death. However, the exact mechanism of OGT-mediated chemotherapy resistance remains unclear. We found that the RNA and protein levels of OGT were decreased in tumor cells under the treatment of UV, adriamycin or cisplatin. We mapped the shortest region in the OGT promoter responding to cisplatin treatment by promoter-reporter assays and used bioinformatics database to predict possible transcription factors that may bind to this region; the candidates we found included p53, C/EBP β, Sp1, E2F and GATA-1. We used cell lines expressing either wild-type p53, mutated p53 or no p53 to observe OGT expression under UV and adriamycin treatment. The results showed that OGT protein levels were decreased under UV and adriamycin treatment regardless of cellular p53 status. Furthermore, overexpression of p53 did not change the protein and RNA levels of OGT. C/EBP β did not have effects on OGT expression, either. Sp1 overexpressed in tumor cells caused an increase in OGT protein levels, but not in RNA levels. Therefore, we have excluded the possibility of p53, C/EBP β, and Sp1 being the transcription factors regulating OGT expression. Moreover, we have tried to study the possible role of OGT in chemotherapy resistance but exogenous expression vectors were not able to restore the expression of OGT under cisplatin treatment. These results suggest that the regulation of OGT in tumor cells is far more complicated than we ever imagined. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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