Suppression of STAT-1 Expression by Human Papillomaviruses Is Necessary for Differentiation-Dependent Genome Amplification and Plasmid Maintenance

High-risk human papillomaviruses (hr-HPV IMPORTANCEHigh-risk HPV can establish persistent infections which may progress to anogenital cancers. hr-HPV interfere with the expression of interferon (IFN)-stimulated genes (ISGs), which is due to reduced levels of IFN-, an IFN that is constitutively expressed in human keratinocytes. This study reveals that IFN-rapidly inhibits HPV transcription and that this is due to the induction of Sp100 proteins. Thus, Sp100 represents an ISG for hr-HPV. P ersistent infections with high-risk human papillomaviruses (hr-HPV) are a necessary risk factor for the development of anogenital and oropharyngeal cancers (1). HPV have circular double-stranded DNA (dsDNA) genomes of ϳ8,000 bp and infect keratinocytes of the basal layer of mucosal and cutaneous epithelium. In undifferentiated cells, HPV genomes replicate as extrachromosomal elements at a low copy number and express only early viral genes such as those for the oncoproteins E6 and E7 and the replication proteins E1, E2, and E8^E2C (2). hr-HPV E6 and E7 interact with critical regulators of the cell cycle such as p53 and retinoblastoma family members to ensure continuous proliferation of infected cells (3).Transcriptome studies have shown that interferon (IFN)-stimulated genes (ISGs) are expressed at lower levels in hr-HPV-positive cell lines than in their uninfected counterparts (4-6). Type I IFNs such as IFN-␣ subtypes or IFN-␤ are induced upon viral infection and then secreted into the extracellular space (7). Secreted IFNs bind to the respective receptor on infected and neighboring cells, and kinases are activated, which results in the nuclear translocation of transcription factors such as STAT1 which then induce several hundred ISGs, many of which have direct antiviral activities (8).The treatment of cell lines that maintain persistently replicating extrachromosomal HPV16 or -31 genomes with recombinant IFN-␤ resulted in growth retardation and the induction of apoptosis, which did not occur with HPV-negative keratinocytes (9, 10). A detailed analysis of the HPV16 copy number and transcription upon IFN-␤ treatment indicated that first the viral copy number is decreased, followed by a reduction of viral transcription (10). HPV31-positive CIN612-9E cells have reduced levels of STAT1, which is both an ISG and also a crucial transcription factor of the IFN signal transduction cascade. Reexpression of STAT1 resulted in a reduction of viral genomes (11). Taken together, these data strongly suggest that IFNs induce ISGs that inhibit the replication of HPV. In line with this, the ISG IFIT1 (or ISG56) directly interacts with the E1 helicases of HPV11 and -18, which results in the inhibition of the replication of the viral origin (12).

supporting

confidence: 48%

“…limit HPV replication (11,12). STAT1 is a crucial transcription factor of the IFN signal transduction cascade, and its anti-HPV activity is most likely due to a reduced expression of a large number of ISGs (7,8).…”

Section: Discussionmentioning

confidence: 99%

Interferon Kappa Inhibits Human Papillomavirus 31 Transcription by Inducing Sp100 Proteins

Habiger

Jäger²,

Walter³

et al. 2016

“…The cells were then grown either in normal growth medium or high calcium medium to induce differentiation. HPV-positive cells amplify episomal DNA upon differentiation in high calcium media within 48 h (26,27). Expression of miR-145 from a heterologous promoter resulted in reduced episomal viral DNA in the undifferentiated cells.…”

mentioning

confidence: 99%

Human Papillomaviruses Modulate MicroRNA 145 Expression To Directly Control Genome Amplification

Gunasekharan

Laimins

2013

Self Cite

H igh-risk human papillomaviruses (HPVs) are the causative agents of cervical and most other anogenital malignancies. Infection by HPVs occurs in the basal layers of stratified epithelia that become exposed due to microabrasions. Following entry, viral genomes are established as low-copy nuclear episomes at approximately 10 to 100 copies per cell (1, 2). In differentiated suprabasal layers, high levels of late gene expression are induced along with genome amplification and virion assembly (3). Two major viral promoters, designated early and late, control transcription during differentiation, but additional regulation also occurs through alternative splicing and other posttranscriptional mechanisms (1, 2, 4). One important mechanism of posttranscriptional control is mediated by small RNAs that are 22 nucleotides in size, referred to as microRNAs (miRNAs). miRNAs bind to partially complementary target sites in mRNA that are often located in the 3=UTR (untranslated regions) but can also be found in coding sequences and the 5=UTR (5). Binding by miRNAs to target sequences results in either the degradation of the target mRNAs or translational repression of the encoded protein (6). A single miRNA can repress the expression of over 100 genes, and a single gene can be repressed by multiple miRNAs. miRNAs often target multiple genes in a pathway and can act cooperatively with other miRNAs (7). Many miRNAs target developmental (8-10) and differentiation pathways (11)(12)(13)(14), as well as cell proliferation and transformation pathways (15-17). Herpesviruses and other small DNA viruses encode their own miRNAs (18); however, this is not the case for HPVs (19). Instead, HPVs modulate expression of host miRNAs to control various aspects of their viral life cycle (20, 21).Several miRNAs have been shown to be modulated by HPV proteins and to play key roles in the viral life cycle. miRNA 203 (miR-203) is a key regulator of epithelial differentiation and is downregulated in HPV-positive cells upon differentiation. This repression allows for the maintenance of high levels of p63, which is normally repressed by miR-203 in differentiating, infected suprabasal cells and is important for maintaining cells in an active state in the cell cycle (21). Additional studies demonstrated miR-218 to be downregulated by HPV E6, which correlates with increased levels of LAMB3, a translational target of this miRNA (22). A number of reports have documented changes in levels of cellular microRNAs in HPV-positive cells using microarray analyses, but only a limited number of studies has examined the significance of these changes in the viral life cycle (23-25).Since HPVs modulate the expression of cellular microRNAs to regulate aspects of their differentiation-dependent life cycle, we sought to identify cellular miRNAs that were altered by HPV proteins in a more physiological context than that reflected in monolayer cultures alone. For this analysis, we performed deep sequencing using organotypic raft cultures of a matched set of normal (viv) and H...

“…Members of the STAT family of transcription factors bind GAS elements, and HPV proteins have been shown to differentially regulate these proteins during the virus life cycle (39)(40)(41)(42), which may help to coordinate the pleiotropic effects observed on the immune system. The time course experiments demonstrated earlier kinetics of IL-18BP expression in E7-expressing cells than in controls.…”

Section: Discussionmentioning

confidence: 99%

Human Papillomavirus E7 Oncoprotein Increases Production of the Anti-Inflammatory Interleukin-18 Binding Protein in Keratinocytes

Richards

Doble

Wasson

et al. 2014

Human papillomavirus (HPV) can successfully evade the host immune response to establish a persistent infection. We show here that expression of the E7 oncoprotein in primary human keratinocytes results in increased production of interleukin-18 (IL-18) binding protein (IL-18BP). This anti-inflammatory cytokine binding protein is a natural antagonist of IL-18 and is necessary for skin homeostasis. We map increased IL-18BP production to the CR3 region of E7 and demonstrate that this ability is shared among E7 proteins from different HPV types. Furthermore, mutagenesis shows that increased IL-18BP production is mediated by a gamma-activated sequence (GAS) in the IL-18BP promoter. Importantly, the increased IL-18BP levels seen in E7-expressing keratinocytes are capable of diminishing IL-18-mediated CD4 lymphocyte activation. This study provides the first evidence for a virus protein that targets IL-18BP and further validates E7 as a key component of the HPV immune evasion armor. IMPORTANCEInfection with human papillomavirus is a leading cause of morbidity and mortality worldwide. This study demonstrates that the E7 protein increases production of the anti-inflammatory IL-18BP, a major regulator of epithelial homeostasis. A number of E7 proteins can increase IL-18BP production, and a region within the CR3 of E7 is necessary for mediating the increase. A consequence of increased IL-18BP production is a reduction in CD4-positive lymphocyte activation in response to IL-18 costimulation. These findings may shed light on the immune evasion abilities of HPV.