Regulation of human papillomavirus type 1 replication by the viral E2 protein

TLR4: An Important Molecule Participating in Either Anti-Human Papillomavirus Immune Responses or Development of Its Related Cancers

It has been reported that human papillomavirus (HPV) is a main cause of cervical cancer. Immune system plays key roles in the HPV infection clearance. Additionally, the roles played by immune responses in development of cancers have been documented previously. Toll-like receptors (TLRs) are the main surface or intravesicular receptors driving innate immunity, which either participate in the fight against infectious agents or participate in the progression of cancers. Thus, it has been hypothesized that the molecules may be part of the HPV/cancers puzzle. TLR4 is a unique member of TLRs family that uses both well-known TLRs related intracellular signaling pathways. Furthermore, the roles played by TLR4 against several viruses and also their related complications, such as tumors, have been demonstrated. Thus, it has been hypothesized that TLR4 may play a key role in HPV infection and its related complications. This review article collected the information regarding the mentioned plausible roles by TLR4.

Inhibition of DNA replication of human papillomavirus by artificial zinc finger proteins

Recently, we demonstrated that plant DNA virus replication was inhibited in planta by using an artificial zinc finger protein (AZP) and created AZP-based transgenic plants resistant to DNA virus infection. Here we apply the AZP technology to the inhibition of replication of a mammalian DNA virus, human papillomavirus type 18 (HPV-18). Two AZPs, designated AZP(HPV)-1 and AZP(HPV)-2, were designed by using our nondegenerate recognition code table and were constructed to block binding of the HPV-18 E2 replication protein to the replication origin. Both of the newly designed AZPs had much higher affinities towards the replication origin than did the E2 protein, and they efficiently blocked E2 binding in vitro. In transient replication assays, both AZPs inhibited viral DNA replication, especially AZP(HPV)-2, which reduced the replication level to approximately 10%. We also demonstrated in transient replication assays, using plasmids with mutant replication origins, that AZP(HPV)-2 could precisely recognize the replication origin in mammalian cells. Thus, it was demonstrated that the AZP technology could be applied not only to plant DNA viruses but also to mammalian DNA viruses.

Identification of a 450-bp region of human papillomavirus type 1 that promotes episomal replication in Saccharomyces cerevisiae

Human papillomaviruses (HPVs) replicate as nuclear plasmids in infected cells. Since the DNA replication machinery is generally conserved between humans and Saccharomyces cerevisiae, we studied whether HPV-1 DNA can replicate in yeast. Plasmids containing a selectable marker (with or without a yeast centromere) and either the full-length HPV-1 genome or various regions of the viral long control region (LCR) and the 3' end of the L1 gene were introduced into S. cerevisiae and their ability to replicate episomally was investigated. Our results show that HPV-1 sequences promote episomal replication of plasmids although the yeast centromere is required for plasmid retention. We have mapped the autonomously replicating sequence activity of HPV-1 DNA to a 450 base-pair sequence (HPV-1 nt 6783-7232) that includes 293 nucleotides from the 5' region of the viral LCR and 157 nucleotides from the 3' end of the L1 gene. The HPV-1 ARS does not include the binding sites for the viral E1 and E2 proteins, and these proteins are dispensable for replication in S. cerevisiae.

mRNA splicing regulates human papillomavirus type 11 E1 protein production and DNA replication

The papillomavirus replicative helicase E1 and the origin recognition protein E2 are required for efficient viral DNA replication. We fused the green fluorescent protein (GFP) to the human papillomavirus type 11 E1 protein either in a plasmid with the E1 coding region alone (nucleotides [nt] 832 to 2781) (pGFP-11E1) or in a plasmid containing both the E1 and E2 regions (nt 2723 to 3826) and the viral origin of replication (ori) (p11Rc). The former supported transient replication of an ori plasmid, whereas the latter was a self-contained replicon. Unexpectedly, these plasmids produced predominantly a cytoplasmic variant GFP or a GFP-E1 E4 protein, respectively. The majority of the mRNAs had an intragenic or intergenic splice from nt 847 to nt 2622 or from nt 847 to nt 3325, corresponding to the E2 or E1 E4 messages. pGFP-11E1dm and p11Rc-E1dm, mutated at the splice donor site, abolished these splices and increased GFP-E1 protein expression. Three novel, alternatively spliced, putative E2 mRNAs were generated in higher abundance from the mutated replicon than from the wild type. Relative to pGFP-11E1, low levels of pGFP-11E1dm supported more efficient replication, but high levels had a negative effect. In contrast, elevated E2 levels always increased replication. Despite abundant GFP-E1 protein, p11Rc-E1dm replicated less efficiently than the wild type. Collectively, these observations show that the E1/E2 ratio is as important as the E1 and E2 concentrations in determining the replication efficiency. These findings suggest that alternative mRNA splicing could provide a mechanism to regulate E1 and E2 protein expression and DNA replication during different stages of the virus life cycle.

Human papillomavirus type 16 status in cervical carcinoma cell DNA assayed by multiplex PCR

Integration of human papillomavirus (HPV) DNA into host genome occurs early in cancer development and is probably an important event in malignant transformation of cervical cancer. The HPV genome integration usually disrupts E2 gene open reading frames. It results in the lack of E2 gene suppressor of the synthesis of E6 and E7 products which, in turn, leads to the overexpression of E6 and E7 genes. The oncogenic HPV types (HPV16, -18, -45, and -58) can be present as episomes or may integrate into human chromosomes. Sixty-six cervical cancer patients positive for HPV16 were tested for the presence of E6, E2, E1, and L1 genes. Multiplex PCR was carried out in all cases. Using cluster analysis, the calculated ratios of E1/E6, E2/E6, L1/E6, E1/E2, and E2/(E1*E6) gene amplification products were divided into two or three statistically different groups. These were used for statistical analysis of the prevalence of specific gene types in histological types of cancer, different levels of clinical staging, and histologically confirmed nodal metastases. The statistical analysis proved a significant correlation in the ratios of E2/E6 and E1/E2 only. The E2/E6 and E1/E2 were higher in carcinoma in situ than in advanced squamous cancers. The E2/E6 ratios were lower in higher clinical stages. The multiplex PCR estimation of the E2/E6 ratio could be a simple method for selecting patients with a high risk of a poor outcome in a standard stage-dependent treatment procedure.

Purification and biochemical characterization of the E1 replication initiation protein of the cutaneous human papillomavirus type 1

The E1 and E2 proteins encoded by papillomaviruses are required for viral DNA replication. Although E1 is the replication initiator protein, previous studies have shown that the full-length E1 protein binds to the origin weakly and with low sequence specificity. The E2 protein facilitates binding of the E1 protein to the origin, triggering the initiation of replication. The E1 protein contains ATPase, helicase and DNA unwinding activities. In vivo studies with mucosal human papillomavirus (HPV) types 11 and 18 have shown that while E1 is absolutely essential for replication, the E1 binding site is dispensable. However, both the E2 protein and E2 binding sites are required for their replication. In contrast to these HPVs, transient replication of HPV type 1, which infects cutaneous tissue, requires only the viral E1 protein and E1 binding site. To understand the basis for these differences, we have overexpressed and purified the HPV-1 E1 and E2 proteins and studied their biochemical properties. The purified E1 protein was shown to have an ATPase activity with a very low K(m) value, similar to that of the SV40 large T antigen. The E1 protein bound to the HPV-1 origin in the absence of the E2 protein and without the use of any cross-linking agents. Our results suggest that the ability of the HPV-1 E1 protein to initiate DNA replication in vivo in the absence of the E2 protein may be due to its stable interaction with the HPV-1 origin.