Novel human papillomavirus type 18 replicon and its application in screening the antiviral effects of cytokines

Treatment with Radix Euphorbiae Ebracteolatae Significantly Decreases the Expression of E6 and L1, and Increases the Expression of p53 and Rb in HPV18-infected Human Foreskin Keratinocytes

BACKGROUND

Radix Euphorbiae Ebracteolatae (REE) was recently reported to be significantly superior to vitamin A acid ointment in treating multiple plantar warts. However, the effects of REE on HPV18 remain unclear. Therefore, the current study aimed to investigate the effects of REE on the proliferation of HPV18, and explore possible molecular mechanisms underlying the effects.

METHODS

HFK and HFK-HPV18 were treated with water-extracted single or compound REE, ethanol-extracted single or compound REE, TNF-α and IFN for 3 days, respectively. In addition, the organotypic rafts containing HFK-HPV18 and HFK were treated with REE, IFN and TNF-α for 7 days, respectively. Cell proliferation rates were measured with Brdu. mRNA expression of E6, L1, p53 and Rb was detected by qPCR. Protein expression of p53, Rb and L1 was detected by Western blot.

RESULTS

Compared to HFK group, HFK-HPV18 group had significantly higher expression of E6 and L1. Compared to the control group, HFK-HPV18 treated with REE, TNF-α and IFN displayed significantly lower proliferation rates. The mRNA expression of E6 was markedly lower, and mRNA expression of p53 and Rb was significantly higher after treatment of REE in HFK-HPV18 or in organotypic rafts containing HFK-HPV18. Treatment with REE markedly increased the protein expression of p53 and Rb, and decreased the protein expression of L1 in HFK-HPV18 or in organotypic rafts containing HFK-HPV18. Among all formula of REE, the inhibition of proliferation rates and expression of E6 and L1, and the increase in expression of p53 and Rb in HFK-HPV18 was highest in ethanol-extracted compound REE group.

CONCLUSIONS

The proliferation rates are significantly lower in HFK-HPV18 treated with REE. The expression of E6 and L1 is markedly lower, and expression of p53 and Rb is significantly higher after REE treatment in HFK-HPV18 or organotypic rafts containing HFK-HPV18. Among all formula of REE, ethanol-extracted compound REE displays the highest protection against HPV18.

Three-dimensional cell culture models for investigating human viruses

Three-dimensional (3D) culture models are physiologically relevant, as they provide reproducible results, experimental flexibility and can be adapted for high-throughput experiments. Moreover, these models bridge the gap between traditional two-dimensional (2D) monolayer cultures and animal models. 3D culture systems have significantly advanced basic cell science and tissue engineering, especially in the fields of cell biology and physiology, stem cell research, regenerative medicine, cancer research, drug discovery, and gene and protein expression studies. In addition, 3D models can provide unique insight into bacteriology, virology, parasitology and host-pathogen interactions. This review summarizes and analyzes recent progress in human virological research with 3D cell culture models. We discuss viral growth, replication, proliferation, infection, virus-host interactions and antiviral drugs in 3D culture models.

Activation of NF-κB by human papillomavirus 16 E1 limits E1-dependent viral replication through degradation of E1

NF-κB 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-κB 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 IκBα and subsequent activation of NF-κB in a manner dependent on helicase activity. Exogenous expression of a degradation-resistant mutant of IκBα, which inhibits the activation of NF-κB, 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-κB 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 IκBα mutant. Collectively, we propose that expression of E1 induces NF-κB activation at least in part through the ATR-dependent DNA damage response and that NF-κB in turn limits E1-dependent replication of HPV16 through degradation of E1, so that E1 and NF-κB 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-κB activation and that this limits E1-dependent genome replication of HPV16. These results suggest that NF-κB 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-κB activity is involved in the establishment and maintenance of persistent HPV infection.

p38MAPK and MK2 pathways are important for the differentiation-dependent human papillomavirus life cycle

Amplification of human papillomaviruses (HPV) is dependent on the ATM DNA damage pathway. In cells with impaired p53 activity, DNA damage repair requires the activation of p38MAPK along with MAPKAP kinase 2 (MK2). In HPV-positive cells, phosphorylation of p38 and MK2 proteins was induced along with relocalization to the cytoplasm. Treatment with MK2 or p38 inhibitors blocked HPV genome amplification, identifying the p38/MK2 pathway as a key regulator of the HPV life cycle.