The modulation and functional regulation of papillomavirus E2 proteins by the cellular sumoylation system : a dissertation /
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| Format: | Thesis Book |
| Language: | English |
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[College Station, Tex.] :
[Texas A&M University System Health Science Center],
[2008]
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| Subjects: |
| Abstract: | ABSTRACT: Papillomaviruses infect cutaneous and mucosal epithelium, and the process of keratinocyte differentiation controls the life cycle of papillomaviruses. Previous studies discovered that papillomavirus E1 helicase was post-translationally modified by a small protein of 12 kDa called SUMO. Our lab determined that sumoylation of E1 affects its nuclear localization and established for the first time a connection between the papillomavirus life cycle and the sumoylation system. Subsequently, we showed that sumoylation levels are up-regulated during keratinocyte differentiation, suggesting a cross-talk between the sumoylation system, papillomavirus infection and the process of keratinocyte differentiation. This study further examined the interplay between cellular sumoylation and papillomavirus proteins during keratinocyte diferentiation, focusing on the viral E2 protein. E2 proteins are critical regulatory proteins that function in many important aspects of the viral life cycle. We used in vitro and in vivo sumoylation assays to demonstrate that E2 proteins are modified by SUMOs. Luciferase assays showed a positive effect of sumoylation on E2 for both transcriptional activation and repression. In addition to the transcriptional regulation of E2 sumoylation, the half-life analysis of intracellular E2 showed that increased overall sumoylation stabilized the HPV 11, 16, and 18 E2 proteins. In vitro studies confirmed that sumoylation could block the proteasomal degradation of the 16E2 protein, likely through inhibition of ubiquitinylation. Altogether, our results suggest that sumoylation has a role in the regulation of papillomaviruses E2 during keratinocyte differentiation. In order to explore the effect of E2 on the host sumoylation system, we performed transient transfection was PHV16 E2 in C33A cells and found that E2 specifically reduced certain cellular SUMO targets. Cellular transcription factor C/EBP has been shown to be involved in both differentiation of keratinocytes and viral transcriptional control of HPV. Our in vivo studies then revealed that HPV E2 decreased the sumoylation level of C/EBP[beta], and that sumoylation of these two proteins appeared to enhance their protein-protein interaction, leading to transcriptional repression of a minimal C/EBP-dependent promoter. In summary, the ability of E2 proteins to modulate the cellular sumoylation system identifies a novel role for HPV in control of the cellular environment. |
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| Item Description: | Vita. "Major Subject: Medical Sciences". "Submitted to the Office of Research and Graduate Studies of The Texas A&M University System Health Science Center in partial fulfillment for the requirements for the degree of Doctor of Philosophy December 2008." Approved as to style and content by: Van G. Wilson, Julian Leibowitz, Steve Maxwell, Susan Payne, John Quarles. |
| Physical Description: | xiii, 210 leaves : illustrations ; 28 cm. |
| Bibliography: | Includes bibliographical references (leaves 205-209). |