p53 Is Regulated in a Biphasic Manner in Hypoxic Human Papillomavirus Type 16 (HPV16)-Positive Cervical Cancer Cells.

Although the effect of hypoxia on p53 in human papillomavirus (HPV)-positive cancer cells has been studied for decades, the impact of p53 regulation on downstream targets and cellular adaptation processes during different periods under hypoxia remains elusive. Here, we show that, despite continuous repression of HPV16 E6/E7 oncogenes, p53 did not instantly recover but instead showed a biphasic regulation marked by further depletion within 24 h followed by an increase at 72 h. Of note, during E6/E7 oncogene suppression, lysosomal degradation antagonizes p53 reconstitution. Consequently, the transcription of p53 responsive genes associated with senescence (e.g., PML and YPEL3) cannot be upregulated. In contrast, downstream genes involved in autophagy (e.g., DRAM1 and BNIP3) were activated, allowing the evasion of senescence under hypoxic conditions. Hence, dynamic regulation of p53 along with its downstream network of responsive genes favors cellular adaptation and enhances cell survival, although the expression of the viral E6/E7-oncogenes as drivers for proliferation remained inhibited under hypoxia.

Combined Transcriptome and Proteome Analysis of Immortalized Human Keratinocytes Expressing Human Papillomavirus 16 (HPV16) Oncogenes Reveals Novel Key Factors and Networks in HPV-Induced Carcinogenesis.

Although the role of high-risk human papillomaviruses (hrHPVs) as etiological agents in cancer development has been intensively studied during the last decades, there is still the necessity of understanding the impact of the HPV E6 and E7 oncogenes on host cells, ultimately leading to malignant transformation. Here, we used newly established immortalized human keratinocytes with a well-defined HPV16 E6E7 expression cassette to get a more complete and less biased overview of global changes induced by HPV16 by employing transcriptome sequencing (RNA-Seq) and stable isotope labeling by amino acids in cell culture (SILAC). This is the first study combining transcriptome and proteome data to characterize the impact of HPV oncogenes in human keratinocytes in comparison with their virus-negative counterparts. To enhance the informative value and accuracy of the RNA-Seq data, four different bioinformatic workflows were used. We identified potential novel upstream regulators (e.g., CNOT7, SPDEF, MITF, and PAX5) controlling distinct clusters of genes within the HPV-host cell network as well as distinct factors (e.g., CPPED1, LCP1, and TAGLN) with essential functions in cancer. Validated results in this study were compared to data sets from The Cancer Genome Atlas (TCGA), demonstrating that several identified factors were also differentially expressed in cervical squamous cell carcinoma and endocervical adenocarcinoma (CESC) and HPV-positive head and neck squamous cell carcinomas (HNSCs). This highly integrative approach allows the identification of novel HPV-induced cellular changes that are also reflected in cancer patients, providing a promising omics data set for future studies in both basic and translational research.IMPORTANCE Human papillomavirus (HPV)-associated cancers still remain a big health problem, especially in developing countries, despite the availability of prophylactic vaccines. Although HPV oncogenes have been intensively investigated for decades, a study applying recent advances in RNA-Seq and quantitative proteomic approaches to a precancerous model system with well-defined HPV oncogene expression alongside HPV-negative parental cells has been missing until now. Here, combined omics analyses reveal global changes caused by the viral oncogenes in a less biased way and allow the identification of novel factors and key cellular networks potentially promoting malignant transformation. In addition, this system also provides a basis for mechanistic research on novel key factors regulated by HPV oncogenes, especially those that are confirmed in vivo in cervical cancer as well as in head and neck cancer patient samples from TCGA data sets.

Systems-level effects of ectopic galectin-7 reconstitution in cervical cancer and its microenvironment.

BACKGROUND: Galectin-7 (Gal-7) is negatively regulated in cervical cancer, and appears to be a link between the apoptotic response triggered by cancer and the anti-tumoral activity of the immune system. Our understanding of how cervical cancer cells and their molecular networks adapt in response to the expression of Gal-7 remains limited. METHODS: Meta-analysis of Gal-7 expression was conducted in three cervical cancer cohort studies and TCGA. In silico prediction and bisulfite sequencing were performed to inquire epigenetic alterations. To study the effect of Gal-7 on cervical cancer, we ectopically re-expressed it in the HeLa and SiHa cervical cancer cell lines, and analyzed their transcriptome and SILAC-based proteome. We also examined the tumor and microenvironment host cell transcriptomes after xenotransplantation into immunocompromised mice. Differences between samples were assessed with the Kruskall-Wallis, Dunn's Multiple Comparison and T tests. Kaplan-Meier and log-rank tests were used to determine overall survival. RESULTS: Gal-7 was constantly downregulated in our meta-analysis (p < 0.0001). Tumors with combined high Gal-7 and low galectin-1 expression (p = 0.0001) presented significantly better prognoses (p = 0.005). In silico and bisulfite sequencing assays showed de novo methylation in the Gal-7 promoter and first intron. Cells re-expressing Gal-7 showed a high apoptosis ratio (p < 0.05) and their xenografts displayed strong growth retardation (p < 0.001). Multiple gene modules and transcriptional regulators were modulated in response to Gal-7 reconstitution, both in cervical cancer cells and their microenvironments (FDR < 0.05 %). Most of these genes and modules were associated with tissue morphogenesis, metabolism, transport, chemokine activity, and immune response. These functional modules could exert the same effects in vitro and in vivo, even despite different compositions between HeLa and SiHa samples. CONCLUSIONS: Gal-7 re-expression affects the regulation of molecular networks in cervical cancer that are involved in diverse cancer hallmarks, such as metabolism, growth control, invasion and evasion of apoptosis. The effect of Gal-7 extends to the microenvironment, where networks involved in its configuration and in immune surveillance are particularly affected.

Post-translational control of IL-1ß via the human papillomavirus type 16 E6 oncoprotein: a novel mechanism of innate immune escape mediated by the E3-ubiquitin ligase E6-AP and p53.

Infections with high-risk human papillomaviruses (HPVs) are causally involved in the development of anogenital cancer. HPVs apparently evade the innate immune response of their host cells by dysregulating immunomodulatory factors such as cytokines and chemokines, thereby creating a microenvironment that favors malignancy. One central key player in the immune surveillance interactome is interleukin-1 beta (IL-1ß) which not only mediates inflammation, but also links innate and adaptive immunity. Because of its pleiotropic physiological effects, IL-1ß production is tightly controlled on transcriptional, post-translational and secretory levels. Here, we describe a novel mechanism how the high-risk HPV16 E6 oncoprotein abrogates IL-1ß processing and secretion in a NALP3 inflammasome-independent manner. We analyzed IL-1ß regulation in immortalized keratinocytes that harbor the HPV16 E6 and/or E7 oncogenes as well as HPV-positive cervical tumor cells. While in primary and in E7-immortalized human keratinocytes the secretion of IL-1ß was highly inducible upon inflammasome activation, E6-positive cells did not respond. Western blot analyses revealed a strong reduction of basal intracellular levels of pro-IL-1ß that was independent of dysregulation of the NALP3 inflammasome, autophagy or lysosomal activity. Instead, we demonstrate that pro-IL-1ß is degraded in a proteasome-dependent manner in E6-positive cells which is mediated via the ubiquitin ligase E6-AP and p53. Conversely, in E6- and E6/E7-immortalized cells pro-IL-1ß levels were restored by siRNA knock-down of E6-AP and simultaneous recovery of functional p53. In the context of HPV-induced carcinogenesis, these data suggest a novel post-translational mechanism of pro-IL-1ß regulation which ultimately inhibits the secretion of IL-1ß in virus-infected keratinocytes. The clinical relevance of our results was further confirmed in HPV-positive tissue samples, where a gradual decrease of IL-1ß towards cervical cancer could be discerned. Hence, attenuation of IL-1ß by the HPV16 E6 oncoprotein in immortalized cells is apparently a crucial step in viral immune evasion and initiation of malignancy.

Epigenetic silencing of interferon-kappa in human papillomavirus type 16-positive cells.

We have investigated interferon-kappa (IFN-kappa) regulation in the context of human papillomavirus (HPV)-induced carcinogenesis using primary human foreskin keratinocytes (HFK), immortalized HFKs encoding individual oncoproteins of HPV16 (E6, E7, and E6/E7), and cervical carcinoma cells. Here, IFN-kappa was suppressed in the presence of E6, whereas its expression was not affected in HFKs or E7-immortalized HFKs. Transcription could be reactivated after DNA demethylation but was decreased again upon drug removal. Partial reactivation could also be accomplished when E6 was knocked down, suggesting a contribution of E6 in IFN-kappa de novo methylation. We identified a single CpG island near the transcriptional start site as being involved in selective IFN-kappa expression. To prove the functional relevance of IFN-kappa in building up an antiviral response, IFN-kappa was ectopically expressed in cervical carcinoma cells where protection against vesicular stomatitis virus-mediated cytolysis could be achieved. Reconstitution of IFN-kappa was accompanied by an increase of p53, MxA, and IFN-regulatory factors, which was reversed by knocking down either IFN-kappa or p53 by small interfering RNA. This suggests the existence of a positive feedback loop between IFN-kappa, p53, and components of IFN signaling pathway to maintain an antiviral state. Our in vitro findings were further corroborated in biopsy samples of cervical cancer patients, in which IFN-kappa was also downregulated when compared with normal donor tissue. This is the first report showing an epigenetic silencing of type I IFN after HPV16 oncogene expression and revealing a novel strategy on how high-risk HPVs can abolish the innate immune response in their genuine host cells.