Alteration of the Epithelial Environment and Cellular Pathways by HPV type 16 E6 and NFX1-123

Thesis (Ph.D.)--University of Washington, 2018High-risk human papillomaviruses (HR HPV) are the causative agent of various anogenital and oropharyngeal cancers, accounting for approximately 5% of the global burden of cancer. The highest risk factor for development of these cancers is a persistent infection with HR HPV. Understanding what promotes long-lived HPV infection is critical for predicting and preventing serious disease outcomes. Persistent infection with HR HPV requires successful propagation in stratified squamous epithelium and is therefore driven by how HR HPVs manipulate the host cell to create an environment beneficial to the viral life cycle. The study of HR HPV, their interactions with the host cell, and how these interactions engender cellular changes that may secondarily lead to oncogenesis is the focus of this dissertation. This dissertation summarizes several ways in which a HR HPV oncoprotein, HPV type 16 E6 (16E6), partners with a host protein, NFX1-123, to manipulate cellular processes and promote its life cycle. Previous work in the laboratory has shown that 16E6 utilizes NFX1-123 to upregulate differentiation markers in keratinocytes; increase levels of Notch1, the master cell fate regulator; and increase expression of telomerase, an enzyme critical to immortalization. The studies presented here further define the cellular processes altered by 16E6 and NFX1-123 to create a cellular milieu beneficial to the viral life cycle. Evasion of the immune response by HR HPVs has been well-documented, but the many molecular mechanisms and protein partners driving these immune deregulatory functions have not yet been fully defined. The data in Chapter 3 establishes 16E6 and NFX1-123 as one such protein partnership through which HR HPVs interfere with the innate immune response and escape detection within infected epithelial cells. Overexpression of NFX1-123 in 16E6 keratinocytes 1) decreased expression of pro-inflammatory cytokines and interferon-stimulated genes (ISGs) at the mRNA and protein level 2) decreased total levels of TRAF6 and TAB2, two proteins in the signaling cascades that govern induction of these antiviral genes and 3) disturbed the normal localization of these signaling proteins. Initiating the immune response within infected keratinocytes is critical for detection of HPV infection and subsequent clearance; deregulating intracellular immune signaling allows HR HPV to avoid detection and resist immune clearance, a necessity for establishing persistent infection. The HPV life cycle is tied to the differentiation programming of epithelial cells, with cellular differentiation driving initiation of the late stage of life viral cycle. Chapter 4 identifies for the first time a role for NFX1-123 in regulating keratinocyte differentiation and late events of the HPV life cycle. NFX1-123 augmented JNK signaling in 16E6 HFKs undergoing differentiation through expression of upstream kinase regulators of JNK, MKK4 and MKK7. Consistent with the connection between the HPV life cycle and differentiation, modulating levels of NFX1-123 in HPV16-positive W12E cells affected late events of the viral life cycle. Altering levels of NFX1-123 resulted in altered mRNA expression levels of L1, the major capsid protein of HPV. 16E6 and NFX1-123 have previously been shown to target the known oncogenic protein telomerase, increasing expression and activity of its catalytic subunit, hTERT. In Chapter 5, we further explore how 16E6 and NFX1-123 targeting of telomerase affects growth and proliferative potential of cells over long term cell culture. The data presented in this chapter demonstrate that NFX1-123 is highly expressed in primary cervical cancers. In vitro, cells expressing 16E6 and overexpressing NFX1-123 had extended active growth, decreased senescence marker staining, and more rapid cell cycling compared to 16E6 expressing cells with endogenous amounts of NFX1-123. These effects on cell proliferation were associated with increased telomerase activity and expression of its catalytic subunit, hTERT. HPV 16-positive cervical cancer cell lines with knocked down NFX1-123 had slowed growth and reduced hTERT. These data indicate that 16E6 and NFX1-123 not only extend proliferative potential of cells via telomerase, but also modify active cellular growth, augment hTERT expression, and increase telomerase activity over time. Altogether, the work in this dissertation describes multiple epithelial cell pathways that HR HPV type 16 E6 and NFX1-123 modify, which subsequently alter the host cell milieu to potentially promote HPV infection and support oncogenic development