Use of an in vivo animal model for assessing the role of integrin α6β4 and Syndecan-1 in early steps in papillomavirus infection

Woodham

et al. 2013

J Virol

159

149

Human papillomaviruses (HPVs) infect epithelia and can lead to the development of lesions, some of which have malignant potential. HPV type 16 (HPV16) is the most oncogenic genotype and causes various types of cancer, including cervical, anal, and head and neck cancers. However, despite significant research, our understanding of the mechanism by which HPV16 binds to and enters host cells remains fragmented. Over several decades, many HPV receptors and entry pathways have been described. This review puts those studies into context and offers a model of HPV16 binding and entry as a framework for future research. Our model suggests that HPV16 binds to heparin sulfate proteoglycans (HSPGs) on either the epithelial cell surface or basement membrane through interactions with the L1 major capsid protein. Growth factor receptors may also become activated through HSPG/growth factor/HPV16 complexes that initiate signaling cascades during early virion-host cell interactions. After binding to HSPGs, the virion undergoes conformational changes, leading to isomerization by cyclophilin B and proprotein convertasemediated L2 minor capsid protein cleavage that increases L2 N terminus exposure. Along with binding to HSPGs, HPV16 binds to ␣6 integrins, which initiate further intracellular signaling events. Following these primary binding events, HPV16 binds to a newly identified L2-specific receptor, the annexin A2 heterotetramer. Subsequently, clathrin-, caveolin-, lipid raft-, flotillin-, cholesterol-, and dynamin-independent endocytosis of HPV16 occurs. Since the discovery of human papillomaviruses (HPVs), researchers in the field have sought to identify the mechanism by which these viruses enter host cells. Although much work has been done to date and many possible receptors have been identified, a clearly defined description of the entry of HPVs has remained controversial. In many cases of viral infection, our understanding of simple binding and uptake through a singular mechanism has given way to a model of a more complex interaction between several specific receptors, coreceptors, and cofactors (1-3). The purpose of this review is to synthesize the known data regarding HPV type 16 (HPV16) binding proteins at the cell surface, and their associated molecules, and attempt to connect them, if possible, into a testable framework of binding and entry. Due to the fact that HPVs are a diverse group of over 150 viruses, this review focuses primarily on the most common of the cancer-causing genotypes, HPV16, while making it clear when non-HPV16 genotypes are reviewed. The development of several HPV particle production systems has allowed researchers to begin to delineate the mechanisms behind viral entry; however, important differences between particles developed in vitro made direct comparisons challenging. Therefore, not only HPV16 structure but also the multiple forms the virus structure takes in the laboratory are discussed below. Finally, due to the tropism of HPV16 for human epithelial cells during a natural infection, this rev...

Section: Hpv16 Binding and Entrymentioning

confidence: 98%

Section: Hpv16 Binding and Entrymentioning

confidence: 99%

The Evolving Field of Human Papillomavirus Receptor Research: a Review of Binding and Entry

Woodham

et al. 2013

J Virol

159

149

“…The proposed secondary HPV receptor integrin α6 can form complexes with either β1 or β4 integrins (Kligys et al, 2012). The possible roles of β subunits as a direct binding partner of HPV virions during infection were investigated, and these studies lead to the conclusion that neither β1 nor β4 showed any direct binding to viral particles (Evander et al, 1997; Huang and Lambert, 2012; Yoon et al, 2001). …”

Section: Introductionmentioning

confidence: 99%

HPV16 infection of HaCaTs is dependent on β4 integrin, and α6 integrin processing

et al. 2014

Our understanding of human papillomavirus (HPV) is still evolving. To further study the field, our laboratory has focused on determining the role of integrins in the initial steps of viral endocytosis into HaCaT cells. Our and others' previous findings have shown that α6 is necessary for infection. Here we show that α3 and β1 were dispensable, and we identified integrin α6β4 complex as necessary for infection in HaCaTs. β4 knock down resulted in a significant decrease in HPV16 PsV infection and perhaps most importantly resulted in defective post-translational α6 processing. We showed that the unprocessed α6 does not localize to the cell surface. We propose that the α6β4 complex is necessary for the formation of an endocytic complex that results in the signaling transduction events necessary for initial endocytosis.

Journal of General Virology

“…As syndecan-1 is the most abundant HSPG expressed on the surface of keratinocytes, it is logical to hypothesize that epithelium infected by HSV has localized increases in the levels of syndecan-1 and syndecan-2, potentially resulting in faster HSPG-mediated binding and subsequent conformational changes of the HPV16 capsid that expose the N terminus of L2 allowing for furin cleavage (Alexopoulou et al, 2007;Raff et al, 2013;Shafti-Keramat et al, 2003). Even though it has been shown that syndecan-1 knockout mice are susceptible to HPV infection, it remains clear that HSPGs play a vital role in initial targeting of virions to the basement membrane, coating of virions with growth factors and other events preceding viral entry (Huang & Lambert, 2012;Surviladze et al, 2012). In summary, our findings demonstrate that molecular changes caused by HSV to the cellular microenvironment promote HPV acquisition in vitro, providing the first evidence for a mechanism that explains the ongoing epidemiological link between HSV infection and HPVassociated cancers.…”

Section: Discussionmentioning

confidence: 99%

Herpes simplex virus downregulation of secretory leukocyte protease inhibitor enhances human papillomavirus type 16 infection

Skeate

Porras

Woodham

et al. 2016

Herpes simplex virus (HSV) was originally implicated in the aetiology of cervical cancer, and although high-risk human papillomavirus (HPV) is now the accepted causative agent, the epidemiological link between HSV and HPV-associated cancers persists. The annexin A2 heterotetramer (A2t) has been shown to mediate infectious HPV type 16 (HPV16) uptake by human keratinocytes, and secretory leukocyte protease inhibitor (SLPI), an endogenous A2t ligand, inhibits HPV16 uptake and infection. Interestingly, HSV infection induces a sustained downregulation of SLPI in epithelial cells, which we hypothesized promotes HPV16 infection through A2t. Here, we show that in vitro infection of human keratinocytes with HSV-1 or HSV-2, but not with an HSV-1 ICP4 deletion mutant that does not downregulate SLPI, leads to a .70 % reduction of SLPI mRNA and a .60 % decrease in secreted SLPI protein.Consequently, we observed a significant increase in the uptake of HPV16 virus-like particles and gene transduction by HPV16 pseudovirions (two-and 2.5-fold, respectively) in HSV-1-and HSV-2-infected human keratinocyte cell cultures compared with uninfected cells, whereas exogenously added SLPI reversed this effect. Using a SiMPull (single-molecule pulldown) assay, we demonstrated that endogenously secreted SLPI interacts with A2t on epithelial cells in an autocrine/paracrine manner. These results suggested that ongoing HSV infection and resultant downregulation of local levels of SLPI may impart a greater susceptibility for keratinocytes to HPV16 infection through the host cell receptor A2t, providing a mechanism that may, in part, provide an explanation for the aetiological link between HSV and HPV-associated cancers.