Activation of NF-κB by Human Papillomavirus 16 E1 Limits E1-Dependent Viral Replication through Degradation of E1

Abstract

NF-B is a family of transcription factors that regulate gene expression involved in many processes, such as the inflammatory response and cancer progression. Little is known about associations of NF-B with the human papillomavirus (HPV) life cycle. We have developed a tissue culture system to conditionally induce E1-dependent replication of the human papillomavirus 16 (HPV16) genome in human cervical keratinocytes and found that expression of HPV16 E1, a viral helicase, results in reduction of IB␣ and subsequent activation of NF-B in a manner dependent on helicase activity. Exogenous expression of a degradation-resistant mutant of IB␣, which inhibits the activation of NF-B, enhanced E1-dependent replication of the viral genome. Wortmannin, a broad inhibitor of phosphoinositide 3-kinases (PI3Ks), and, to a lesser extent, VE-822, an ATR kinase inhibitor, but not KU55933, an ATM kinase inhibitor, suppressed the activation of NF-B and augmented E1-dependent replication of the HPV16 genome. Interestingly, the enhancement of E1-dependent replication of the viral genome was associated with increased stability of E1 in the presence of wortmannin as well as the IB␣ mutant. Collectively, we propose that expression of E1 induces NF-B activation at least in part through the ATR-dependent DNA damage response and that NF-B in turn limits E1-dependent replication of HPV16 through degradation of E1, so that E1 and NF-B may constitute a negative feedback loop. IMPORTANCE A major risk factor in human papillomavirus (HPV)-associated cancers is persistent infection with high-risk HPVs. To eradicate viruses from infected tissue, it is important to understand molecular mechanisms underlying the establishment and maintenance of persistent infection. In this study, we obtained evidence that human papillomavirus 16 (HPV16) E1, a viral DNA helicase essential for amplification of the viral genomes, induces NF-B activation and that this limits E1-dependent genome replication of HPV16. These results suggest that NF-B mediates a negative feedback loop to regulate HPV replication and that this feedback loop could be associated with control of the viral copy numbers. We could thus show for the first time that NF-B activity is involved in the establishment and maintenance of persistent HPV infection. Human papillomaviruses (HPVs) are a large family of nonenveloped, small DNA viruses with an approximately 8-kbp double-stranded circular genome that infect stratified squamous epithelium in various anatomical sites such as skin, the anogenital tract, and the oral cavity. Virus infection can cause hyperproliferative lesions, ranging from verrucae to cancer. To date, at least 180 types of HPVs have been cloned from clinical lesions and classified as either cutaneous or mucosal types based on their predilection for different sites of infection. A subset of mucosal HPVs, high-risk HPVs (HR-HPVs), such as HPV16, are strongly associated with anogenital cancers, including nearly 100% of cervical cancers and some proportion of head and neck cancers...

HPV16 and 18 genome amplification show different E4-dependence, with 16E4 enhancing E1 nuclear accumulation and replicative efficiency via its cell cycle arrest and kinase activation functions

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DNA Damage Signalling and Repair Inhibitors: The Long-Sought-After Achilles’ Heel of Cancer

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Immunhistochemical analysis of Nuclear Factor Kappa Beta expression in etiopathogenesis of ovarian tumors

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