Human Papillomaviruses Target the DNA Damage Repair and Innate Immune Response Pathways to Allow for Persistent Infection

Targeting ATR Pathway in Solid Tumors: Evidence of Improving Therapeutic Outcomes

The DNA damage response (DDR) system is a complicated network of signaling pathways that detects and repairs DNA damage or induces apoptosis. Critical regulators of the DDR network include the DNA damage kinases ataxia telangiectasia mutated Rad3-related kinase (ATR) and ataxia-telangiectasia mutated (ATM). The ATR pathway coordinates processes such as replication stress response, stabilization of replication forks, cell cycle arrest, and DNA repair. ATR inhibition disrupts these functions, causing a reduction of DNA repair, accumulation of DNA damage, replication fork collapse, inappropriate mitotic entry, and mitotic catastrophe. Recent data have shown that the inhibition of ATR can lead to synthetic lethality in ATM-deficient malignancies. In addition, ATR inhibition plays a significant role in the activation of the immune system by increasing the tumor mutational burden and neoantigen load as well as by triggering the accumulation of cytosolic DNA and subsequently inducing the cGAS-STING pathway and the type I IFN response. Taken together, we review stimulating data showing that ATR kinase inhibition can alter the DDR network, the immune system, and their interplay and, therefore, potentially provide a novel strategy to improve the efficacy of antitumor therapy, using ATR inhibitors as monotherapy or in combination with genotoxic drugs and/or immunomodulators.

Regulatory Effect of Ficus carica Latex on Cell Cycle Progression in Human Papillomavirus-Positive Cervical Cancer Cell Lines: Insights from Gene Expression Analysis

Cervical cancer presents a significant global health concern with high-risk human papillomaviruses (HPVs) identified as the main cause of this cancer. Although current treatment methods for cervical cancer can eliminate lesions, preventing metastatic spread and minimizing tissue damage remain a major challenge. Therefore, the development of a safer and innovative therapeutic approach is of the utmost importance. Natural products like fig latex, derived from the Ficus carica tree, have demonstrated promising anti-cancer properties when tested on cervical cancer cell lines. However, the specific mechanisms by which fig latex exerts its effects are still unknown. In this study, we conducted RNA-Seq analysis to explore how fig latex may counteract carcinogenesis in HPV-positive cervical cancer cell lines, namely, CaSki (HPV type 16-positive) and HeLa (HPV type 18-positive). Our results from this investigation indicate that fig latex influences the expression of genes associated with the development and progression of cervical cancer, including pathways related to "Nonsense-Mediated Decay (NMD)", "Cell Cycle regulation", "Transcriptional Regulation by TP53", and "Apoptotic Process". This selective impact of fig latex on cancer-related pathways suggests a potential novel therapeutic approach for HPV-related cervical cancer.

For Better or Worse: Modulation of the Host DNA Damage Response by Human Papillomavirus

High-risk human papillomaviruses (HPVs) are associated with several human cancers. HPVs are small, DNA viruses that rely on host cell machinery for viral replication. The HPV life cycle takes place in the stratified epithelium, which is composed of different cell states, including terminally differentiating cells that are no longer active in the cell cycle. HPVs have evolved mechanisms to persist and replicate in the stratified epithelium by hijacking and modulating cellular pathways, including the DNA damage response (DDR). HPVs activate and exploit DDR pathways to promote viral replication, which in turn increases the susceptibility of the host cell to genomic instability and carcinogenesis. Here, we review recent advances in our understanding of the regulation of the host cell DDR by high-risk HPVs during the viral life cycle and discuss the potential cellular consequences of modulating DDR pathways.

Advances in autophagy modulation of natural products in cervical cancer

ETHNOPHARMACOLOGICAL RELEVANCE

Natural products play a critical role in drug development and is emerging as a potential source of biologically active metabolites for therapeutic intervention, especially in cancer therapy. In recent years, there is increasing evidence that many natural products may modulate autophagy through various signaling pathways in cervical cancer. Understanding the mechanisms of these natural products helps to develop medications for cervical cancer treatments.

AIM OF THE STUDY

In recent years, there is increasing evidence that many natural products may modulate autophagy through various signaling pathways in cervical cancer. In this review, we briefly introduce autophagy and systematically describe several classes of natural products implicated in autophagy modulation in cervical cancer, hoping to provide valuable information for the development of cervical cancer treatments based on autophagy.

MATERIALS AND METHODS

We searched for studies on natural products and autophagy in cervical cancer on the online database and summarized the relationship between natural products and autophagy modulation in cervical cancer.

RESULTS

Autophagy is a lysosome-mediated catabolic process in eukaryotic cells that plays an important role in a variety of physiological and pathological processes, including cervical cancer. Abnormal expression of cellular autophagy and autophagy-related proteins has been implicated in cervical carcinogenesis, and human papillomavirus infection can affect autophagic activity. Flavonoids, alkaloids, polyphenols, terpenoids, quinones, and other compounds are important sources of natural products that act as anticancer agents. In cervical cancer, natural products exert the anticancer function mainly through the induction of protective autophagy.

CONCLUSIONS

The regulation of cervical cancer autophagy by natural products has significant advantages in inducing apoptosis, inhibiting proliferation, and reducing drug resistance in cervical cancer.

The Drivers, Mechanisms, and Consequences of Genome Instability in HPV-Driven Cancers

Simple Summary

Cells infected with high-risk human papillomaviruses (HPV) can accumulate DNA damage and eventually transform into HPV-driven cancers. Genome instability, or the progressive accumulation of DNA alterations (e.g., mutations), in HPV-infected cells is directly induced by the HPV genes and indirectly promoted by HPV infection through the consequences of chronic infection maintenance, increased cell growth, and accumulation of damaging mutations in genes that themselves affect genome instability. While the HPV genome typically exists as a separate entity within cells, genome instability increases the chances of HPV integrating within the host (human) genome, which is common in HPV-induced cancers. The DNA regions surrounding HPV integrations are unstable and can undergo complex alterations that affect both human and HPV genes. This review discusses HPV-dependent and -independent drivers and mechanisms of genome instability in HPV-driven cancers, both globally and around sites of HPV integration, and describes the changes induced in the tumour genome.

Abstract

Human papillomavirus (HPV) is the causative driver of cervical cancer and a contributing risk factor of head and neck cancer and several anogenital cancers. HPV’s ability to induce genome instability contributes to its oncogenicity. HPV genes can induce genome instability in several ways, including modulating the cell cycle to favour proliferation, interacting with DNA damage repair pathways to bring high-fidelity repair pathways to viral episomes and away from the host genome, inducing DNA-damaging oxidative stress, and altering the length of telomeres. In addition, the presence of a chronic viral infection can lead to immune responses that also cause genome instability of the infected tissue. The HPV genome can become integrated into the host genome during HPV-induced tumorigenesis. Viral integration requires double-stranded breaks on the DNA; therefore, regions around the integration event are prone to structural alterations and themselves are targets of genome instability. In this review, we present the mechanisms by which HPV-dependent and -independent genome instability is initiated and maintained in HPV-driven cancers, both across the genome and at regions of HPV integration.

Regulation of the Innate Immune Response during the Human Papillomavirus Life Cycle

High-risk human papillomaviruses (HR HPVs) are associated with multiple human cancers and comprise 5% of the human cancer burden. Although most infections are transient, persistent infections are a major risk factor for cancer development. The life cycle of HPV is intimately linked to epithelial differentiation. HPVs establish infection at a low copy number in the proliferating basal keratinocytes of the stratified epithelium. In contrast, the productive phase of the viral life cycle is activated upon epithelial differentiation, resulting in viral genome amplification, high levels of late gene expression, and the assembly of virions that are shed from the epithelial surface. Avoiding activation of an innate immune response during the course of infection plays a key role in promoting viral persistence as well as completion of the viral life cycle in differentiating epithelial cells. This review highlights the recent advances in our understanding of how HPVs manipulate the host cell environment, often in a type-specific manner, to suppress activation of an innate immune response to establish conditions supportive of viral replication.

Human papillomaviruses sensitize cells to DNA damage induced apoptosis by targeting the innate immune sensor cGAS

The cyclic GMP-AMP synthase (cGAS) is a critical regulator of the innate immune response acting as a sensor of double-strand DNAs from pathogens or damaged host DNA. Upon activation, cGAS signals through the STING/TBK1/IRF3 pathway to induce interferon expression. Double stranded DNA viruses target the cGAS pathway to facilitate infection. In HPV positive cells that stably maintain viral episomes, the levels of cGAS were found to be significantly increased over those seen in normal human keratinocytes. Furthermore the downstream effectors of the cGAS pathway, STING and IRF3, were fully active in response to signaling from the secondary messenger cGAMP or poly (dA:dT). In HPV positive cells cGAS was detected in both cytoplasmic puncta as well as in DNA damage induced micronuclei. E6 was responsible for increased levels of cGAS that was dependent on inhibition of p53. CRISPR-Cas9 mediated knockout of cGAS prevented activation of STING and IRF3 but had a minimal effect on viral replication. A primary function of cGAS in HPV positive cells was in response to treatment with etoposide or cisplatin which lead to increased levels of H2AX phosphorylation and activation of caspase 3/7 cleavage while having only a minimal effect on activation of homologous recombination repair factors ATM, ATR or CHK2. In HPV positive cells cGAS was found to regulate the levels of the phosphorylated non-homologous end-joining kinase, DNA-PK, which may contribute to H2AX phosphorylation along with other factors. Importantly cGAS was also responsible for increased levels of DNA breaks along with enhanced apoptosis in HPV positive cells but not in HFKs. This study identifies an important and novel role for cGAS in mediating the response of HPV positive cells to chemotherapeutic drugs.

Persistent infection by human papillomaviruses (HPV) is the major risk factor for development of cervical as well as other anogenital and oropharyngeal cancers. Innate immune surveillance pathways are important in determining whether HPV infections will be cleared or persist. The role and activity of cGAS, an innate immune DNA sensor, during HPV infection is still not well understood. In this study we characterized the activity of cGAS-STING pathway in cells that stably maintain high-risk HPV episomes and found it was fully active. Furthermore, our studies indicate that cGAS helps regulate the response to DNA damage causing drugs such as etoposide and cisplatin. Treatment with both drugs further increased the levels of cGAS in HPV positive cells and this was critical for causing DNA breaks along with apoptotic cell death. These findings identify a novel role of cGAS in HPV positive cells in regulating the response to chemotherapeutic DNA damaging agents.

ATM Pathway Is Essential for HPV–Positive Human Cervical Cancer-Derived Cell Lines Viability and Proliferation

Infection with some mucosal human papillomavirus (HPV) types is the etiological cause of cervical cancer and of a significant fraction of vaginal, vulvar, anal, penile, and head and neck carcinomas. DNA repair machinery is essential for both HPV replication and tumor cells survival suggesting that cellular DNA repair machinery may play a dual role in HPV biology and pathogenesis. Here, we silenced genes involved in DNA Repair pathways to identify genes that are essential for the survival of HPV-transformed cells. We identified that inhibition of the ATM/CHK2/BRCA1 axis selectively affects the proliferation of cervical cancer-derived cell lines, without altering normal primary human keratinocytes (PHK) growth. Silencing or chemical inhibition of ATM/CHK2 reduced the clonogenic and proliferative capacity of cervical cancer-derived cells. Using PHK transduced with HPV16 oncogenes we observed that the effect of ATM/CHK2 silencing depends on the expression of the oncogene E6 and on its ability to induce p53 degradation. Our results show that inhibition of components of the ATM/CHK2 signaling axis reduces p53-deficient cells proliferation potential, suggesting the existence of a synthetic lethal association between CHK2 and p53. Altogether, we present evidence that synthetic lethality using ATM/CHK2 inhibitors can be exploited to treat cervical cancer and other HPV-associated tumors.

TLR9 in the Human Papilloma Virus Infections: Friend or Foe?

Immune system plays dual roles during human papilloma virus (HPV) infections, from defense against the virus to induction or stimulation of the HPV-related cancers. It appears that various differences within the immune-related genes and the functions of the immunological parameters of the patients are the main factors responsible for the roles played by immune system during HPV infections. Toll-like receptors (TLRs) play key roles in the recognition of viruses and activation of immune responses. The molecules also can alter the target cell intracellular signaling and may participate in the transformation of the infected cells. TLR9 is the unique intracellular member of TLRs that recognize foreign DNA, including viral DNA. Thus, TLR9 may play significant roles in the defense against HPV and its related cancers. This review article discusses TLR9 antiviral and pathological roles during HPV infection.

Molecular Mechanisms of HIV Protease Inhibitors Against HPV-Associated Cervical Cancer: Restoration of TP53 Tumour Suppressor Activities

Cervical cancer is a Human Papilloma virus-related disease, which is on the rise in a number of countries, globally. Two essential oncogenes, E6 and E7, drive cell transformation and cancer development. These two oncoproteins target two of the most important tumour suppressors, p53 and pRB, for degradation through the ubiquitin ligase pathway, thus, blocking apoptosis activation and deregulation of cell cycle. This pathway can be exploited for anticancer therapeutic interventions, and Human Immunodeficiency Virus Protease Inhibitors (HIV-PIs) have attracted a lot of attention for this anticancer drug development. HIV-PIs have proven effective in treating HPV-positive cervical cancers and shown to restore impaired or deregulated p53 in HPV-associated cervical cancers by inhibiting the 26S proteasome. This review will evaluate the role players, such as HPV oncoproteins involved cervical cancer development and how they are targeted in HIV protease inhibitors-induced p53 restoration in cervical cancer. This review also covers the therapeutic potential of HIV protease inhibitors and molecular mechanisms behind the HIV protease inhibitors-induced p53-dependent anticancer activities against cervical cancer.

Immunotherapeutic Approaches for the Treatment of HPV-Associated (Pre-)Cancer of the Cervix, Vulva and Penis

Human papillomavirus (HPV) infection drives tumorigenesis in almost all cervical cancers and a fraction of vulvar and penile cancers. Due to increasing incidence and low vaccination rates, many will still have to face HPV-related morbidity and mortality in the upcoming years. Current treatment options (i.e., surgery and/or chemoradiation) for urogenital (pre-)malignancies can have profound psychosocial and psychosexual effects on patients. Moreover, in the setting of advanced disease, responses to current therapies remain poor and nondurable, highlighting the unmet need for novel therapies that prevent recurrent disease and improve clinical outcome. Immunotherapy can be a useful addition to the current therapeutic strategies in various settings of disease, offering relatively fewer adverse effects and potential improvement in survival. This review discusses immune evasion mechanisms accompanying HPV infection and HPV-related tumorigenesis and summarizes current immunotherapeutic approaches for the treatment of HPV-related (pre-)malignant lesions of the uterine cervix, vulva, and penis.

HPV16 Entry into Epithelial Cells: Running a Gauntlet

During initial infection, human papillomaviruses (HPV) take an unusual trafficking pathway through their host cell. It begins with a long period on the cell surface, during which the capsid is primed and a virus entry platform is formed. A specific type of clathrin-independent endocytosis and subsequent retrograde trafficking to the trans-Golgi network follow this. Cellular reorganization processes, which take place during mitosis, enable further virus transport and the establishment of infection while evading intrinsic cellular immune defenses. First, the fragmentation of the Golgi allows the release of membrane-encased virions, which are partially protected from cytoplasmic restriction factors. Second, the nuclear envelope breakdown opens the gate for these virus–vesicles to the cell nucleus. Third, the dis- and re-assembly of the PML nuclear bodies leads to the formation of modified virus-associated PML subnuclear structures, enabling viral transcription and replication. While remnants of the major capsid protein L1 and the viral DNA remain in a transport vesicle, the viral capsid protein L2 plays a crucial role during virus entry, as it adopts a membrane-spanning conformation for interaction with various cellular proteins to establish a successful infection. In this review, we follow the oncogenic HPV type 16 during its long journey into the nucleus, and contrast pro- and antiviral processes.