Extended effects of human papillomavirus 16 E6-specific short hairpin RNA on cervical carcinoma cells

Distinguishing Genetic Drift from Selection in Papillomavirus Evolution

Pervasive purifying selection on non-synonymous substitutions is a hallmark of papillomavirus genome history, but the role of selection on and the drift of non-coding DNA motifs on HPV diversification is poorly understood. In this study, more than a thousand complete genomes representing Alphapapillomavirus types, lineages, and SNP variants were examined phylogenetically and interrogated for the number and position of non-coding DNA sequence motifs using Principal Components Analyses, Ancestral State Reconstructions, and Phylogenetic Independent Contrasts. For anciently diverged Alphapapillomavirus types, composition of the four nucleotides (A, C, G, T), codon usage, trimer usage, and 13 established non-coding DNA sequence motifs revealed phylogenetic clusters consistent with genetic drift. Ancestral state reconstruction and Phylogenetic Independent Contrasts revealed ancient genome alterations, particularly for the CpG and APOBEC3 motifs. Each evolutionary analytical method we performed supports the unanticipated conclusion that genetic drift and different evolutionary drivers have structured Alphapapillomavirus genomes in distinct ways during successive epochs, even extending to differences in more recently formed variant lineages.

Single-Domain Antibodies Represent Novel Alternatives to Monoclonal Antibodies as Targeting Agents against the Human Papillomavirus 16 E6 Protein

Approximately one fifth of all malignancies worldwide are etiologically associated with a persistent viral or bacterial infection. Thus, there is a particular interest in therapeutic molecules which use components of a natural immune response to specifically inhibit oncogenic microbial proteins, as it is anticipated they will elicit fewer off-target effects than conventional treatments. This concept has been explored in the context of human papillomavirus 16 (HPV16)-related cancers, through the development of monoclonal antibodies and fragments thereof against the viral E6 oncoprotein. Challenges related to the biology of E6 as well as the functional properties of the antibodies themselves appear to have precluded their clinical translation. Here, we addressed these issues by exploring the utility of the variable domains of camelid heavy-chain-only antibodies (denoted as VHHs). Through construction and panning of two llama, immune VHH phage display libraries, a pool of potential VHHs was isolated. The interactions of these with recombinant E6 were further characterized using an enzyme-linked immunosorbent assay (ELISA), Western blotting under denaturing and native conditions, and surface plasmon resonance. Three VHHs were identified that bound recombinant E6 with nanomolar affinities. Our results lead the way for subsequent studies into the ability of these novel molecules to inhibit HPV16-infected cells in vitro and in vivo.

The miRNA23b-regulated signaling network as a key to cancer development--implications for translational research and therapeutics

A growing body of evidence indicates that microRNA23b (miR23b) is pleiotropic-it plays important roles in regulating physiological functions of cells, in regulating differentiation of cells and in regulating cellular immune responses. Our review of the literature showed that dysregulation of miR23b expression is implicated in the disruption of these cellular mechanisms and development of diseases such as cancer. MiR23b dysregulation appears to do this by modulating the expression level of candidate gene products involved in a network of signaling pathways including TGF-beta and Notch pathways that govern malignant properties of cancer cells such as motility and invasiveness. More recently, miR23b regulation of gene expression has also been associated with cancer stem cells and chemoresistance. Our review covers miR23b's role in immunity, endothelial function, differentiation, and cancer as well as its potential for translation into future cancer diagnostics and therapeutics.

The small splice variant of HPV16 E6, E6, reduces tumor formation in cervical carcinoma xenografts

High-risk types of human papillomavirus (HPV) cause nearly all cases of cervical cancer. The E6 oncoprotein is produced as a full-length variant (E6) as well as several shorter isoforms (E6). E6 inhibits certain oncogenic activities of E6, suggesting that it might play an anti-oncogenic role in vivo. To test this, we created E6-expressing SiHa (HPV(+)) and C33A (HPV(-)) cells, then examined the ability of both the parental and E6-expressing cells to form tumors in nude mice. We found that over-expression of E6 indeed decreased the growth of tumors derived from both SiHa and C33A cells, with the reduction greatest in tumors derived from E6-expressing SiHa cells. These findings point to multiple anti-oncogenic characteristics of E6, some of which likely involve down-regulation of the full-length isoform, and others that are independent of HPV. These data represent the first demonstration of biologically-relevant E6 activities distinct from those of the full-length isoform in vivo.

Human papillomavirus type 16 E6 induces cervical cancer cell migration through the p53/microRNA-23b/urokinase-type plasminogen activator pathway

Deregulation of microRNA (miRNA or miR) expression in human cervical cancer is associated frequently with human papillomavirus (HPV) integration. miR-23b is often downregulated in HPV-associated cervical cancer. Interestingly, urokinase-type plasminogen activator (uPA), the miR-23b target, is detected in cervical cancer, but not in normal cervical tissues. Thus, the importance of miR-23b and uPA in HPV-associated cervical cancer development is investigated. In this study, the high-risk subtype HPV-16 E6 oncoprotein was found to decrease the expression of miR-23b, increase the expression of uPA, and thus induce the migration of human cervical carcinoma SiHa and CaSki cells. uPA is the target gene for miR-23b as the miR repressed uPA expression and interacted with the 3'-untranslated region of uPA mRNA. The tumor suppressor p53 is known to be inactivated by HPV-16 E6. A consensus p53 binding site is detected in the promoter region of miR-23b, whereas p53 trans-activated and also interacted with the miR's promoter. Therefore, p53 is believed to mediate the HPV-16 E6 downregulation of miR-23b. From the above, miR-23b/uPA are confirmed to be involved in HPV-16 E6-associated cervical cancer development.

Lentiviral delivery of short hairpin RNAs

In less than a decade after discovery, RNA interference-mediated gene silencing is already being tested as potential therapy in clinical trials for a number of diseases. Lentiviral vectors provide a means to express short hairpin RNA (shRNA) to induce stable and long-term gene silencing in both dividing and non-dividing cells and thus, are being intensively investigated for this purpose. However, induction of long-term shRNA expression can also cause toxicities by inducing off-target effects and interference with the endogenous micro-RNA (miRNA) pathway that regulates cellular gene expression. Recently, several advances have been made in the shRNA vector design to mimic cellular miRNA processing and to express multiplex siRNAs in a tightly regulated and reversible manner to overcome toxicities. In this review we describe some of these advances, focusing on the progress made in the development of lentiviral shRNA delivery strategies to combat viral infections.

Novel anti-metastatic action of cidofovir mediated by inhibition of E6/E7, CXCR4 and Rho/ROCK signaling in HPV tumor cells

Cervical cancer is frequently associated with HPV infection. The expression of E6 and E7 HPV oncoproteins is a key factor in its carcinogenicity and might also influence its virulence, including metastatic conversion. The cellular mechanisms involved in metastatic spread remain elusive, but pro-adhesive receptors and their ligands, such as SDF-1α and CXCR4 are implicated. In the present study, we assessed the possible relationship between SDF-1α/CXCR4 signaling, E6/E7 status and the metastatic process. We found that SDF-1α stimulated the invasion of E6/E7-positive cancer cell lines (HeLa and TC-1) in Matrigel though CXCR4 and subsequent Rho/ROCK activation. In pulmonary metastatic foci generated by TC-1 cells IV injection a high proportion of cells expressed membrane-associated CXCR4. In both cases models (in vitro and in vivo) cell adhesion and invasion was abrogated by CXCR4 immunological blockade supporting a contribution of SDF-1α/CXCR4 to the metastatic process. E6 and E7 silencing using stable knock-down and the approved anti-viral agent, Cidofovir decreased CXCR4 gene expression as well as both, constitutive and SDF-1α-induced cell invasion. In addition, Cidofovir inhibited lung metastasis (both adhesion and invasion) supporting contribution of E6 and E7 oncoproteins to the metastatic process. Finally, potential signals activated downstream SDF-1α/CXCR4 and involved in lung homing of E6/E7-expressing tumor cells were investigated. The contribution of the Rho/ROCK pathway was suggested by the inhibitory effect triggered by Cidofovir and further confirmed using Y-27632 (a small molecule ROCK inhibitor). These data suggest a novel and highly translatable therapeutic approach to cervix cancer, by inhibition of adhesion and invasion of circulating HPV-positive tumor cells, using Cidofovir and/or ROCK inhibition.

Inhibition of cervical cancer cell growth by human papillomavirus virus-like particles packaged with human papillomavirus oncoprotein short hairpin RNAs

Overexpression of human papillomavirus (HPV E6 and HPV E7) oncogenes in human cervical cells results in the development of cancer, and E6 and E7 proteins are therefore targets for preventing cervical cancer progression. Here, we describe the silencing of E6 and E7 expression in cervical carcinoma cells by RNA interference. In order to increase the efficacy of the RNA interference, HPV pseudovirions coding for a short hairpin RNA (shRNA) sequence were produced. The results indicated the degradation of E6 and E7 mRNAs when shRNA against E6 or E7 were delivered by pseudovirions in HPV-positive cells (CaSki and TC1 cells). E6 silencing resulted in the accumulation of cellular p53 and reduced cell viability. More significant cell death was observed when E7 expression was suppressed. Silencing E6 and E7 and the consequences for cancer cell growth were also investigated in vivo in mice using the capacity of murine TC1 cells expressing HPV-16 E6 and E7 oncogenes to induce fast-growing tumors. Treatment with lentiviruses and HPV virus-like particle vectors coding for an E7 shRNA sequence both resulted in dramatic inhibition of tumor growth. These results show the ability of pseudovirion-delivered shRNA to produce specific gene suppression and provide an effective means of reducing HPV-positive tumor growth.

Signaling of DNA damage is not sufficient to induce p53 response: (Re)Activation of wt p53 protein strongly depends on cellular context

It is generally accepted that exposure of cells to a variety of DNA-damaging agents leads to up-regulation and activation of wild-type (wt) p53 protein. We investigated the (re)-activation of p53 protein in two human cancer cell lines in which the gene for this tumor suppressor is not mutated: HeLaS(3) cervix carcinoma and MCF-7 breast cancer cells, by induction via different genotoxic and cytotoxic stimuli. Treatment of human cells with the alkylating agent N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) or different anti-cancer drugs resulted in a strong DNA damage as evidenced by Comet assay and a marked increase in site-specific phosphorylation of H2AX. Unlike in MCF-7 cells, in HeLaS(3) cells the expression of p53 protein did not increase after MNNG treatment despite a strong DNA damage. However, other agents for example doxorubicin markedly induced p53 response in HeLaS(3) cells. After exposure of these cells to MNNG, the ATM-dependent effector proteins Chk2 and NBS1 were phosphorylated, thereby evidencing that MNNG-induced DNA breakage was recognized and properly signaled. In HeLaS(3) cells wt p53 protein is not functional due to E6-mediated targeting for accelerated ubiquitylation and degradation. Therefore, the activation of a p53 response to genotoxic stress in HeLaS(3) cells seems to depend on the status of E6 oncoprotein. Indeed, the induction of p53 protein in HeLaS(3) cells in response to distinct agents inversely correlates with the cellular level of E6 oncoprotein. This implicates that the capability of different agents to activate p53 in HeLaS(3) cells primarily depends on their inhibitory effect on expression of E6 oncoprotein.

Suppression of cervical carcinoma cell growth by intracytoplasmic codelivery of anti-oncoprotein E6 antibody and small interfering RNA

Cervical cancer is caused by high-risk types of human papillomaviruses (HPV) that encode the E6 and E7 oncogenes. Silencing of E6 gene expression in HPV-positive cell lines by transfection of small interfering RNA (siRNA) with cationic lipids restores the dormant p53 tumor suppressor pathway. Because cationic lipids can also be used for intracytoplasmic delivery of proteins, we tested whether the delivery of monoclonal antibodies that bind to HPV16 E6 and neutralize its biological activity in vitro could restore p53 function in tumor cells. Here, we show that the 4C6 antibody is efficiently delivered into the cell cytoplasm using a lipidic reagent used for siRNA transfection. The delivery of 4C6 resulted in the nuclear accumulation of p53 protein in CaSki and SiHa cells but not in HeLa cells. Furthermore, the antibody-mediated p53 response was dramatically increased when a peptide corresponding to the 4C6 epitope and bearing a COOH-terminal cysteine residue was added to the transduction mixture. We found that a fraction of the added peptides were dimers that allowed the formation of antibody polymers adsorbed onto the lipidic matrix. With this system, the proliferation of CaSki and SiHa cells was strongly diminished, but no apoptosis was detectable. Remarkably, cell growth was almost totally suppressed by the addition of E6-specific siRNA to the transduction complex. The results indicate that the activity of E6 oncoprotein can be down-regulated in vivo by lipid-mediated antibody delivery and that antibodies and siRNA act synergistically when codelivered. This novel targeting strategy is simple to implement and may find therapeutic applications.

Virally mediated cervical cancer in the iatrogenically immunocompromised: applications for psychoneuroimmunology

Oncogenic or high-risk (HR) human papillomavirus (HPV) infection is implicated in the pathogenesis of a number of cancers, including cervical cancer. HPV infected individuals who are immunocompromised secondary to acquired (e.g., human immunodeficiency virus [HIV]) or iatrogenic (e.g., systemic lupus erythematosus [SLE] patients and organ and hematopoeitic stem cell transplant recipients undergoing immunosuppressive therapy) immune deficiency are particularly at risk for HPV-initiated cervical neoplasia and cancer. Psychoneuroimmunologic (PNI) research has demonstrated that psychosocial factors such as stress, pessimism, and sleep quality may play a role in the promotion of HPV-mediated cervical neoplasia in HIV-positive women. However, no research to our knowledge has examined PNI mechanisms of HPV-mediated cervical neoplasia and cancer in women who are undergoing iatrogenic immunosuppressive therapy for the treatment of autoimmune disease or the prevention of graft-rejection. This article reviews the PNI mechanisms that may underlie the promotion of HPV-mediated cervical neoplasia and applies this model to HPV-infected women who are iatrogenically immunosuppressed, an understudied population at-risk for cervical cancer. Female transplant recipients, one such group, may provide a unique paradigm in which to explore further PNI mechanisms of HPV-mediated cervical neoplasia.

Antisense RNA directed to the human papillomavirus type 16 E7 mRNA from herpes simplex virus type 1 derived vectors is expressed in CaSki cells and downregulates E7 mRNA

BACKGROUND

Human papillomavirus (HPV) infection is known to be the most important etiologic factor of cervical cancer. There is no HPV specific therapy available for treatment of invasive squamous cell carcinoma of the cervix and its precursor lesions. The present study elucidates the potential to use herpes simplex virus (HSV) derived vectors for expression of antisense RNA to HPV -16 E7 oncogene.

RESULTS

We have constructed replication competent, nonneuroinvasive HSV-1 vectors, deleted of the gamma134.5 gene. The vectors express RNA antisense to the first 100 nucleotides of the HPV-16 E7 gene. We assayed the ability of the antisense E7 vectors R5225 (tk-) and R5226 (tk+), to produce antisense RNA, as well as the consequent effects on E7 mRNA and protein levels in HPV-16 positive CaSki cells. Anti-E7 RNA was expressed by both constructs in a dose-dependent manner. Expression of HPV-16 E7 mRNA was downregulated effectively in CaSki cells infected with the tk- recombinant R5225 or with R5226. The tk+ recombinant R5226 was effective in downregulating E7 protein expression.

CONCLUSION

We have shown that anti-E7 RNA expressed from an HSV vector could efficiently downregulate HPV-16 E7 mRNA and E7 protein expression in CaSki cells. We conclude that HSV vectors may become a useful tool for gene therapy of HPV infections.