The Effect of Quercetin on the Growth of Primary Bovine Cells and Analysis of Its Ability to Modulate the Level of Transcription from the Bovine Papillomavirus Type 4 Long Control Region

Connolly, Julie-Anne Catherine (1997) The Effect of Quercetin on the Growth of Primary Bovine Cells and Analysis of Its Ability to Modulate the Level of Transcription from the Bovine Papillomavirus Type 4 Long Control Region. PhD thesis, University of Glasgow.

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It has been demonstrated that the bioflavonoid quercetin can synergise with bovine papillomavirus type 4 (BPV4) DNA plus an activated ras oncogene to fully transform primary fibroblasts cells derived from bovine foetal palate (PalF cells). The aim of this thesis has been to identify a mechanism(s) by which quercetin may be contributing to this transformation process. Quercetin was shown to inhibit the growth of PalF cells in a concentration dependent maimer. A quercetin concentration of ~20?M inhibited the growth of PalF cells by approximately 50%. PalF cells were shown to arrest in the G1/G0 and G2/M phases of the cell cycle in response to quercetin treatment. These results indicated that the presence of quercetin in PalF cell culture medium is not conducive to normal cell proliferation. Investigations were undertaken to determine if quercetin could modulate the level of transcription from the viral long control region (LCR); this region of the virus contains sequences which are involved in regulating expression of viral genes. Results showed that quercetin was capable of increasing the level of viral transcription from the LCR up to 4 fold. In keeping with earlier observations, the timing of exposure to quercetin was critical; the increase in transcription from the viral LCR was only observed when cell were exposed to quercetin after cells had been transfected with LCR-containing reporter plasmids. No effect on transcription was observed when cells were treated with quercetin before transfection. The quercetin- mediated effect on LCR transcription activity was also limited to the LCR functioning in a promoter capacity. Quercetin had no effect on the LCR when present as an enhancer. Removal of nucleotides 311 to 331 from the 3'terminal end of the BPV4 LCR correlated with a drop in the basal level of transcription from the LCR and abrogation of the response of the LCR to quercetin. EMSA experiments identified a cellular factor, designated QX1, as binding to an oligonucleotide corresponding the sequence of the LCR from nucleotides 301 to 331. Although this sequence of the LCR contains a TRE-like binding motif, mutational analysis has confirmed that this motif is not the site to which QX1 specifically binds. Furthermore, AP-1 does not bind to the TRE- like element. API and QX1 display different mobilities in a polyacrylamide gel showing that QX1 and API are not the same factor. Mutational analysis has thus far not identified specific residues critical for the binding of QX1 to this 3' terminal region of the BPV4 LCR. Western blot analysis, using a phosphotyrosine antibody, identified several proteins which showed changes in their phosphotyrosine status in response to quercetin exposure. These results confirm that quercetin can alter the phosphorylation status, and possibly also the activity of a number of different proteins, in PalF cells. The observations made in the course of this thesis indicate that quercetin can induce PalF cells to growth arrest, possibly as a result of DNA damage. Quercetin also causes an increase in the level of viral transcription. Over-expression of viral oncoproteins such as E7, in response to quercetin treatment, would stimulate cells to continue proliferating. The stimulation of damaged cells to proliferate in an adverse environment induced by quercetin may partially explain the ability of quercetin to transform PalF cells in co-operation with BPV4 plus ras. Other epigenetic effects, as indicated by the changes induced in several phosphotyrosine-containing proteins, could further contribute to this synergism.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Additional Information: Adviser: Saveria M Campo
Keywords: Medicine, Pharmacology
Date of Award: 1997
Depositing User: Enlighten Team
Unique ID: glathesis:1997-74880
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 27 Sep 2019 15:42
Last Modified: 27 Sep 2019 15:42

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