Date Approved

8-2017

Document Type

Dissertation

Degree Name

PhD in Cell & Molecular Biology

Department

Molecular Biology

College

Graduate School of Biomedical Science

First Advisor

Subhasis Biswas, PhD

Committee Member 1

Salvatore Caradonna, PhD

Committee Member 2

Jennifer Fischer, PhD

Committee Member 3

Susan Muller-Weeks, PhD

Committee Member 4

Esther Biswas-Fiss, PhD

Subject(s)

Human Papillomavirus Viruses, Viral Envelope Proteins, DNA Replication, Carcinogenesis, Binding Sites, Virus Replication

Disciplines

Cancer Biology | Cell Biology | Cellular and Molecular Physiology | Laboratory and Basic Science Research | Medicine and Health Sciences | Molecular Biology | Molecular Genetics | Neoplasms | Virology | Virus Diseases

Abstract

Human papillomaviruses are a vast family of double-stranded DNA viruses containing non-carcinogenic and carcinogenic types, whose crucial differences remain unknown, except for the difference in the frequency of DNA replication. The human papillomavirus (HPV) E2 protein regulates the initiation of viral DNA replication and transcription. Its recognition and binding to four 12 bp palindromic sequences in the viral origin is essential for its function. Little is known about the DNA binding mechanism of the E2 protein found in HPV types that have low risk for oncogenicity (low-risk) as well as the roles of various elements of the individual binding sites. The binding sites in the origin of all HPVs are separated by variable spacer and flanking regions; however, their importance in E2-DNA recognition and regulation remains unclear. Analysis of low-risk E2 DNA binding affinity unraveled multiple sequence elements that appeared to influence target discrimination including the sequence of spacer region, flanking sequences, and proximity of E2 binding sites. The results for the low-risk E2 were compared to those of the E2 encoded by HPVs that have high risk for oncogenicity (high-risk). Single nucleotide variations in the high-risk E2 binding sites were identified by sequence analysis of carcinogenic and non-carcinogenic HPVs. Sequence variations in binding sites of carcinogenic HPVs were correlated to attenuated formation of the E2-DNA complex. Differences in E2 binding in the origin of carcinogenic and non-carcinogenic HPVs were observed. Further analysis of viral replication initiation included the assessment of E2 in the presence of the HPV E1 helicase, also required in this process. The fundamental biochemical properties of the E1-E2-DNA complex formation were evaluated. E1 was localized to the DNA by E2 bound to the DNA, through E1-E2 protein interactions. The data presented here suggests the mechanism of E1-E2 interaction at the origin in HPV DNA replication initiation. E2 binding to the origin is tightly linked to the activation of the DNA replication origin as well as initiation of DNA replication. Together, these results allow us to elucidate a model for replication initiation in carcinogenic and non-carcinogenic HPVs and propose a correlation to HPV-mediated cellular carcinogenesis.

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