Pericentromeric regions are refractory to prompt repair after replication stress-induced breakage in HPV16 E6E7-expressing epithelial cells

Targeting HPV in gynaecological cancers - Current status, ongoing challenges and future directions

Despite the success of preventive vaccination, the Human Papilloma Virus still accounts for 266,000 deaths annually, as the main causative factor of cervical, vaginal, anal, penile and oropharyngeal cancers. Human Papilloma Virus infects epithelial cells, driving tumourigenesis primarily from incorporation of DNA into the host cellular genome. Translation of two particular Human Papilloma Virus-specific oncoproteins, E6 and E7, are the key drivers of malignancy. If diagnosed early cervical, vaginal and vulval cancers have good prognosis and are treated with curative intent. However, metastatic disease carries a poor prognosis, with first-line systemic treatment providing only modest increase in outcome. Having shown promise in other solid malignancies, immune checkpoint inhibition and therapeutic cancer vaccines have been directed towards Human Papilloma Virus-associated gynaecological cancers, mindful that persistent Human Papilloma Virus infection drives malignancy and is associated with immunosuppression and lack of T-cell immunity. In this review, we discuss novel therapeutic approaches for targeting Human Papilloma Virus-driven gynaecological malignancies including vaccination strategies, use of immunomodulation, immune checkpoint inhibitors and agents targeting Human Papilloma Virus-specific oncoproteins. We also highlight the evolving focus on exciting new treatments including adoptive T-cell therapies.

DGCR8/miR-106 Axis Enhances Radiosensitivity of Head and Neck Squamous Cell Carcinomas by Downregulating RUNX3

Purpose: Head and neck squamous cell carcinoma (HNSCC) is the sixth most prevalent malignant tumor worldwide, and the radiotherapy effect is strongly associated with human papillomavirus (HPV) infection. Therefore, the aim of our study was to analyze the mechanism of HPV E7 and its effects on radiosensitivity in HNSCC cells. Methods: The mRNA expression of DiGeorge syndrome critical region gene 8 (DGCR8), has-miR-106a, and Runt-related transcription factor 3 (RUNX3) was examined by quantitative real-time PCR (RT-qPCR). The protein expression of DGCR8, E7, RUNX3, caspase-3/cleaved caspase-3, poly(ADP-ribose) polymerase (PARP)/cleaved PARP, and γH2AX was measured by Western blot. The expression level of DGCR8 was measured by immunofluorescence assay. Starbase database (http://starbase.sysu.edu.cn/) was used to analyze the correlation between has-miR-106a-5p and DGCR8. TargetScan database (http://www.targetscan.org/vert_72/) was adopted to calculate the prediction of binding sites. Radiosensitivity was evaluated through clone formation assays and Cell Counting Kit-8 (CCK-8) assays. Results: In our study, we found that the mRNA and protein expression levels of HPV E7 and DGCR8 in HPV-positive HNSCC cells were higher than those in HPV-negative cells. The expression of DGCR8 was increased in FaDu and UM-SCC-4 with E7 overexpression, while the expression of DGCR8 was decreased in UM-SCC-47 and UPCI-SCC-090 with E7 silence. The miR-106a expression was increased after DGCR8 overexpression in FaDu and UM-SCC-4. However, the miR-106a expression was decreased in UM-SCC-47 and UPCI-SCC-090 with E7 silence. In radiation conditions, clone formation assays found that less clones formed in FaDu and UM-SCC-4 cells subsequent to silencing DGCR8 or miR-106a than that in the control group, and more clones were formed in UM-SCC-47 and UPCI-SCC-090 cells overexpressing DGCR8 or miR-106a than that in the control group. Luciferase reporter gene assays verified that miR-106a targeted the 3' untranslated region (UTR) of RUNX3 mRNA. MiR-106a overexpression resulted in a decrease in RUNX3 expression, and miR-106a silence increased RUNX3 expression. Rescue experiments conducted with miR-106a inhibitor restored radiation resistance and reduced DNA damage in radiation condition. Conclusions: Our study indicated that HPV E7 activated DGCR8/miR-106a/RUNX3 axis to enhance radiation sensitivity and provided directions for targeted therapeutic interventions.

DNMT1 Enhances the Radiosensitivity of HPV-Positive Head and Neck Squamous Cell Carcinomas via Downregulating SMG1

Introduction

Head and neck squamous cell carcinoma (HNSCC), which rank the 7th malignant tumors worldwide, is closely related to methylation and HPV infection. Ionizing radiation therapy is the main strategy for HNSCC patients in advanced stage. Previously, HPV-positive HNSCC predict better prognosis than HPV-negative HNSCCs under radiotherapy, however its molecular mechanism is unresolved. SMG1 serves as a potential tumor suppressor in various cancers, including HNSCC.

Methods

The mRNAs and proteins expression of HPV E6/E7, p16, p53, DNMT1, SMG1 were detected after different treatments by qPCR and Western blot. The clone formation ability was measured in radiation dose after different treatments.

Results

In our study, the expression of HPV16 E6, DNA Methyltransferase 1(DNMT1) and SMG1 in head and neck carcinomas cell lines was detected by RT-qPCR and Western blot. Forced E6 level in HPV-negative cells by overexpression plasmid promoted the expression of DNMT1, which resulted in decreased SMG1 expression. Silenced SMG1 in HPV-negative HNSCC cells elicited increased radiation sensitivity, suggesting that SMG1 may be an effective switch to regulate the effect of radiotherapy in HNSCC.

Conclusion

Our study indicated that DNMT1 enhances the radiosensitivity of HPV-positive head and neck squamous cell carcinomas via downregulating SMG1.

Methylation of global DNA repeat LINE-1 and subtelomeric DNA repeats D4Z4 in leukocytes is associated with biochemical recurrence in African American prostate cancer patients

Global DNA methylation may play important roles in cancer etiology and prognosis. The goal of this study is to investigate whether the methylation of long interspersed nucleotide elements (LINE-1) and subtelomeric DNA repeats D4Z4 in leukocyte DNA is associated with aggressive prostate cancer (PCa) in African Americans. We measured DNA methylation levels of LINE-1 and D4Z4 in 306 African American (AA) PCa patients using pyrosequencing and compared their methylation levels among clinical variables. We further applied multivariate Cox proportional hazards model and Kaplan-Meier survival function and log-rank tests to assess the association between DNA methylation and biochemical recurrence (BCR). Overall, there was no significant difference of the methylation levels of LINE-1 and D4Z4 among patients with different clinical and epidemiological characteristics. However, the methylation of LINE-1 and D4Z4 was associated with BCR. Patients with lower LINE-1 methylation and higher D4Z4 methylation exhibited markedly increased risks of BCR with adjusted hazard ratios of 3.34 (95% confidence interval, 1.32-8.45) and 4.12 (95% confidence interval, 1.32-12.86), respectively, and significantly shorter BCR-free survival times. Our results suggest that lower global DNA methylation and higher subtelomeric region methylation may predict worse prognosis in localized AA PCa patients.

Genome-wide Control of Heterochromatin Replication by the Telomere Capping Protein TRF2

Hard-to-replicate regions of chromosomes (e.g., pericentromeres, centromeres, and telomeres) impede replication fork progression, eventually leading, in the event of replication stress, to chromosome fragility, aging, and cancer. Our knowledge of the mechanisms controlling the stability of these regions is essentially limited to telomeres, where fragility is counteracted by the shelterin proteins. Here we show that the shelterin subunit TRF2 ensures progression of the replication fork through pericentromeric heterochromatin, but not centromeric chromatin. In a process involving its N-terminal basic domain, TRF2 binds to pericentromeric Satellite III sequences during S phase, allowing the recruitment of the G-quadruplex-resolving helicase RTEL1 to facilitate fork progression. We also show that TRF2 is required for the stability of other heterochromatic regions localized throughout the genome, paving the way for future research on heterochromatic replication and its relationship with aging and cancer.

Methylation of subtelomeric repeat D4Z4 in peripheral blood leukocytes is associated with biochemical recurrence in localized prostate cancer patients

Global DNA methylation may affect chromosome structure and genomic stability and is involved in carcinogenesis. In this study, we aimed to investigate whether methylation of pericentromeric repeat NBL2 and subtelomeric repeat D4Z4 in peripheral blood was associated with the aggressiveness of prostate cancer (PCa). We measured the methylation status of different CpG sites of NBL2 and D4Z4 in 795 PCa patients and compared their methylation levels among patients with different Gleason Score at diagnosis. We then analyzed the association of the NBL2 and D4Z4 methylation with the risk of biochemical recurrence (BCR) in patients receiving radical prostatectomy or radiotherapy using a multivariate Cox proportional hazards model. In addition, we used the Kaplan-Meier survival function and log-rank tests to assess BCR-free survival associated with D4Z4 methylation. There was no significant difference in methylation level of NBL2 and D4Z4 between clinically defined aggressive and non-aggressive PCa at diagnosis. However, the methylation of D4Z4 was associated with BCR, while the methylation of NBL2 was not. In tertile analysis, patients in the highest tertile of D4Z4 methylation had an increased risk of BCR (HR = 2.17, 95% CI 1.36-3.48) compared to patients in the lower tertiles after adjustment of age, body mass index, smoking status, pack year, D'Amico risk groups and treatments. Among the four CpG sites in this region, the association was mostly attributable to the methylation of the second CpG site of D4Z4. These data suggest that higher methylation in D4Z4 was associated with worse prognosis of localized PCa patients.

Centromere Stability: The Replication Connection

The fission yeast centromere, which is similar to metazoan centromeres, contains highly repetitive pericentromere sequences that are assembled into heterochromatin. This is required for the recruitment of cohesin and proper chromosome segregation. Surprisingly, the pericentromere replicates early in the S phase. Loss of heterochromatin causes this domain to become very sensitive to replication fork defects, leading to gross chromosome rearrangements. This review examines the interplay between components of DNA replication, heterochromatin assembly, and cohesin dynamics that ensures maintenance of genome stability and proper chromosome segregation.

Breaking the DNA damage response to improve cervical cancer treatment

Every year, cervical cancer affects ∼500,000 women worldwide, and ∼275,000 patients die of this disease. The addition of platin-based chemotherapy to primary radiotherapy has increased 5-year survival of advanced-stage cervical cancer patients, which is, however, still only 66%. One of the factors thought to contribute to treatment failure is the ability of tumor cells to repair chemoradiotherapy-induced DNA damage. Therefore, sensitization of tumor cells for chemoradiotherapy via inhibition of the DNA damage response (DDR) as a novel strategy to improve therapy effect, is currently studied pre-clinically as well as in the clinic. Almost invariably, cervical carcinogenesis involves infection with the human papillomavirus (HPV), which inactivates part of the DNA damage response. This HPV-mediated partial inactivation of the DDR presents therapeutic targeting of the residual DDR as an interesting approach to achieve chemoradio-sensitization for cervical cancer. How the DDR can be most efficiently targeted, however, remains unclear. The fact that cisplatin and radiotherapy activate multiple signaling axes within the DDR further complicates a rational choice of therapeutic targets within the DDR. In this review, we provide an overview of the current preclinical and clinical knowledge about targeting the DDR in cervical cancer.

The CINs of the centromere

Replication stress is a significant contributor to genome instability. Recent studies suggest that the centromere is particularly susceptible to replication stress and prone to rearrangements and genome damage, as well as chromosome loss. This effect is enhanced by loss of heterochromatin. The resulting changes in genetic organization, including chromosome loss, increased mutation and loss of heterozygosity, are important contributors to malignant growth.