Diffusible VP22–E2 Protein Kills Bystander Cells and Offers a Route for Cervical Cancer Gene Therapy

Utilization of a cell-penetrating peptide-adaptor for delivery of human papillomavirus protein E2 into cervical cancer cells to arrest cell growth and promote cell death

BACKGROUND

Human papillomavirus (HPV) is the causative agent of nearly all forms of cervical cancer, which can arise upon viral integration into the host genome and concurrent loss of viral regulatory gene E2. Gene-based delivery approaches show that E2 reintroduction reduces proliferative capacity and promotes apoptosis in vitro.

AIMS

This work explored if our calcium-dependent protein-based delivery system, TAT-CaM, could deliver functional E2 protein directly into cervical cancer cells to limit proliferative capacity and induce cell death.

MATERIALS AND RESULTS

TAT-CaM and the HPV16 E2 protein containing a CaM-binding sequence (CBS-E2) were expressed and purified from Escherichia coli. Calcium-dependent binding kinetics were verified by biolayer interferometry. Equimolar TAT-CaM:CBS-E2 constructs were delivered into the HPV16+ SiHa cell line and uptake verified by confocal microscopy. Proliferative capacity was measured by MTS assay and cell death was measured by release of lactate dehydrogenase. As a control, human microvascular cells (HMECs) were used. As expected, TAT-CaM bound CBS-E2 with high affinity in the presence of calcium and rapidly disassociated upon its removal. After introduction by TAT-CaM, fluorescently labeled CBS-E2 was detected in cellular interiors by orthogonal projections taken at the depth of the nucleus. In dividing cells, E2 relocalized to regions associated with the mitotic spindle. Cells receiving a daily dose of CBS-E2 for 4 days showed a significant reduction in metabolic activity at low doses and increased cell death at high doses compared to controls. This phenotype was retained for 7 days with no further treatments. When subcultured on day 12, treated cells regained their proliferative capacity.

CONCLUSIONS

Using the TAT-CaM platform, bioactive E2 protein was delivered into living cervical cancer cells, inducing senescence and cell death in a time- and dose-dependent manner. These results suggest that this nucleic acid and virus-free delivery method could be harnessed to develop novel, effective protein therapeutics.

Controversies surrounding human papilloma virus infection, head & neck vs oral cancer, implications for prophylaxis and treatment

Head & Neck Cancer (HNC) represents the sixth most common malignancy worldwide and it is historically linked to well-known behavioural risk factors, i.e., tobacco smoking and/or the alcohol consumption. Recently, substantial evidence has been mounting that Human Papillomavirus (HPV) infection is playing an increasing important role in oral cancer. Because of the attention and clamor surrounding oral HPV infection and related cancers, as well as the use of HPV prophylactic vaccines, in this invited perspective the authors raise some questions and review some controversial issues on HPV infection and its role in HNC, with a particular focus on oral squamous cell carcinoma.

The problematic definition and classification of HNC will be discussed, together with the characteristics of oral infection with oncogenic HPV types, the frequency of HPV DNA detection in HNC, the location of HPV-related tumours, the severity and prognosis of HPV-positive HNC, the diagnosis of oral HPV infection, common routes of oral infection and the likelihood of oro-genital HPV transmission, the prevention of HPV infection and novel therapeutic approaches.

A cancer cell-specific inducer of apoptosis

Human papillomavirus (HPV) DNA is found in virtually all cervical cancers, strongly suggesting that these viruses are necessary to initiate this disease. The HPV E2 protein is required for viral replication, but E2 expression is usually lost in HPV-transformed cells because of the integration of viral DNA into the host chromosome. Several studies have shown that the reintroduction of E2 into HPV-transformed cells can induce growth arrest and apoptotic cell death. This raises the possibility that E2 could be useful in the treatment of HPV-induced disease. However, the effects of E2 on cell proliferation are not limited to HPV-transformed cells. The E2 protein from HPV type 16 can induce apoptosis via at least two pathways. One pathway involves the binding of E2 to p53 and operates in HPV-transformed cells, many non-HPV-transformed cell lines, and untransformed normal cells. The second pathway requires the binding of E2 to the viral genome and operates only in HPV-transformed cells. A mutation in E2 that significantly reduces the binding of this protein to p53 abrogates the induction of apoptosis in non-HPV-transformed cells and normal cells, but has no effect on the ability of the mutated protein to induce apoptosis in HPV-transformed cells. Here we show that a chimeric protein consisting of this mutant of E2, fused to the herpes simplex virus type 1 VP22 protein, can traffic between cells in a three-dimensional tumor model and induce apoptosis in HPV-transformed cells with high specificity. This cancer cell-specific inducer of apoptosis may be useful in the treatment of cervical cancer and other HPV-induced diseases.

Replication-competent herpes simplex virus 1 isolates selected from cells transfected with a bacterial artificial chromosome DNA lacking only the UL49 gene vary with respect to the defect in the UL41 gene encoding host shutoff RNase

To generate a null U(L)49 gene mutant of herpes simplex virus 1 (HSV-1), we deleted from the viral DNA, encoded as a bacterial artificial chromosome (BAC), the U(L)49 open reading frame and, in a second step, restored it. Upon transfection into Vero cells, the BAC-DeltaU(L)49 DNA yielded foci of degenerated cells that could not be expanded and a few replication-competent clones. The replication-competent viral clones derived from independent transfections yielded viruses that expressed genes with some delay, produced smaller plaques, and gave lower yields than wild-type virus. A key finding is that the independently derived replication-competent viruses lacked the virion host shutoff (vhs) activity expressed by the RNase encoded by the U(L)41 gene. One mutant virus expressed no vhs protein, whereas two others, derived from independent transfections, produced truncated vhs proteins consistent with the spontaneous in-frame deletion. In contrast, cells infected with the virus recovered upon transfection of the BAC-U(L)49R DNA (R-U(L)49) accumulated a full-length vhs protein, indicating that in the parental BAC-DeltaU(L)49 DNA, the U(L)41 gene was intact. We conclude that expression of the vhs protein in the absence of U(L)49 protein is lethal, a conclusion bolstered by the evidence reported elsewhere that in transfected cells vhs requires both VP16 and VP22, the product of U(L)49, to be neutralized.

Evidence for intercellular trafficking of VP22 in living cells

The intercellular trafficking property of the herpes simplex virus type 1 tegument protein VP22 makes it a promising tool for overcoming low transduction efficiencies in gene therapy. However, recent reports suggest not only that VP22 cannot facilitate intercellular spreading and that trafficking of VP22 fusion proteins results from artifacts of cell fixation only. To provide direct evidence for the presence or absence of VP22-mediated intercellular trafficking, we generated an adenoviral vector with a dual expression cassette for VP22 fused to green fluorescent protein (VP22 GFP) and DsRed under the control of distinct human cytomegalovirus immediate-early enhancer/promoter regions. Using this vector, we were able to distinguish clearly between primary transduced cells and cells taking up VP22GFP by intercellular trafficking. To our knowledge, for the first time, we could demonstrate by live-cell confocal fluorescence microscopy that VP22GFP can be found intracellularly in unfixed recipient cells. The extent of VP22 spread was similar in paraformaldehyde-fixed cells and unfixed cells as demonstrated by fluorescence-activated cell sorting analysis. We thus confirmed the ability of VP22-mediated intercellular trafficking in live unfixed cells.

Effect of cell-based intercellular delivery of transcription factor GATA4 on ischemic cardiomyopathy

Recent loss-of-function studies highlight the importance of the transcription factor GATA4 in the myocardial response to injury in the adult heart. However, the potential effects of gain-in-function of GATA4 overexpression, and transcription factors in general, is hindered by the fact that transcription factors are neither secreted nor taken up by cells. Chimeric proteins incorporating motifs of cell-penetrating proteins are secreted from cells and internalized by surrounding cells. We engineered a chimeric protein consisting of GATA4 and the cell-penetrating protein VP22. Cardiac fibroblasts stably transfected with the GATA4:VP22, GFP:VP22, or green fluorescent protein (GFP) constructs were transplanted into Lewis rats 1 month after left anterior descending ligation. GATA4:VP22 expression in the border zone was associated with increased cardiac myosin expression and cardiac myocyte size (30 mum versus 19 mum, P<0.01). Compared with the GFP:VP22 control group, 6 weeks after cardiac fibroblast transplantation (10 weeks after myocardial infarction), animals that received GATA4:VP22-expressing cardiac fibroblasts demonstrated increased cardiac function and less negative remodeling. These data demonstrate a novel strategy for transcription factor delivery to injured myocardium and indicate that the delivery of GATA4 locally to the infarct border zone induces multiple local effects in the border zone cardiac myocytes resulting in beneficial ventricular remodeling and improved global left ventricular function.

Development of a topical protein therapeutic for human papillomavirus and associated cancers

Human papillomaviruses (HPVs) are the causative agents of several disease states, including genital warts and cervical cancer. There are around 500 million cases of genital warts per annum worldwide and around 450,000 cases of cervical cancer. Although HPV vaccines should eventually reduce the incidence of these diseases, new and effective treatments are still urgently required. The E2 (early) proteins from some HPV types induce growth arrest and apoptosis, and these proteins could be used as therapeutics for HPV-induced disease. A major obstacle to this approach concerns the delivery of the protein to HPV-transformed cells and/or HPV-infected cells in vivo. One possible solution is to use recombinant viruses to deliver E2. Another possible solution is to use purified E2 proteins or E2 fusion proteins. The herpes simplex virus VP22 protein is one of a small number of proteins that have been shown to cross the cell membrane with high efficiency. VP22-E2 fusion proteins produced in bacterial cells are able to enter mammalian cells and induce apoptosis. This suggests that VP22-E2 fusion proteins could be topically applied as a treatment for HPV-induced diseases, most probably post-surgery. In this review, we discuss this and other approaches to the topical delivery of selective therapeutic agents against HPV-associated conditions.

Papillomavirus proteins and their potential as drug design targets

The papillomaviruses are a family of small, double-stranded DNA viruses that infect the basal cells of cutaneous and mucosal epithelium. While a large percentage of the population is benignly infected with various strains of human papillomavirus (HPV), long-term infection by a subset of HPV strains is associated with malignant transformation. The prospects for prophylaxis against HPV infection have recently received an enormous boost with the approval by the US FDA of a vaccine targeted against the most common cancer-associated HPV strains. However, the large number of people already infected, the high cost of the vaccination regimen (particularly in poorer countries) and the HPV infections that these vaccines do not protect against underscore the need for therapeutic strategies. The elucidation of molecular details underlying fundamental processes in the viral life cycle, such as virus replication, transcription and HPV-induced carcinogenesis, is required to meet this aim. This article provides an overview of high-resolution structures of papillomavirus proteins and their functional complexes, with particular reference to mechanistic and structural features that could be exploited in the rational design of antiviral agents.