The p16-specific reactivation and inhibition of cell migration through demethylation of CpG islands by engineered transcription factors

Driving effect of P16 methylation on telomerase reverse transcriptase-mediated immortalization and transformation of normal human fibroblasts

BACKGROUND

P16 inactivation is frequently accompanied by telomerase reverse transcriptase (TERT) amplification in human cancer genomes. P16 inactivation by DNA methylation often occurs automatically during immortalization of normal cells by TERT. However, direct evidence remains to be obtained to support the causal effect of epigenetic changes, such as P16 methylation, on cancer development. This study aimed to provide experimental evidence that P16 methylation directly drives cancer development.

METHODS

A zinc finger protein-based P16-specific DNA methyltransferase (P16-Dnmt) vector containing a "Tet-On" switch was used to induce extensive methylation of P16 CpG islands in normal human fibroblast CCD-18Co cells. Battery assays were used to evaluate cell immortalization and transformation throughout their lifespan. Cell subcloning and DNA barcoding were used to track the diversity of cell evolution.

RESULTS

Leaking P16-Dnmt expression (without doxycycline-induction) could specifically inactivate P16 expression by DNA methylation. P16 methylation only promoted proliferation and prolonged lifespan but did not induce immortalization of CCD-18Co cells. Notably, cell immortalization, loss of contact inhibition, and anchorage-independent growth were always prevalent in P16-Dnmt&TERT cells, indicating cell transformation. In contrast, almost all TERT cells died in the replicative crisis. Only a few TERT cells recovered from the crisis, in which spontaneous P16 inactivation by DNA methylation occurred. Furthermore, the subclone formation capacity of P16-Dnmt&TERT cells was two-fold that of TERT cells. DNA barcoding analysis showed that the diversity of the P16-Dnmt&TERT cell population was much greater than that of the TERT cell population.

CONCLUSION

P16 methylation drives TERT-mediated immortalization and transformation of normal human cells that may contribute to cancer development.

Homocysteine facilitates endoplasmic reticulum stress and apoptosis of hepatocytes by suppressing ERO1α expression via cooperation between DNMT1 and G9a

Endoplasmic reticulum (ER) stress and apoptosis play a critical role in liver injury. Endoplasmic reticulum oxidoreductase 1α (ERO1α) is an oxidase that exists in the luminal side of the ER membrane, participating in protein folding and secretion and inhibiting apoptosis, but the underlying mechanism on liver injury induced by homocysteine (Hcy) remains obscure. In this study, hyperhomocysteinemia (HHcy) mice model was established in cbs^+/− mice by feeding a high‐methionine diet for 12 weeks; and cbs^+/− mice fed with high‐methionine diet exhibited more severe liver injury compared to cbs^+/+ mice. Mechanistically, we found that Hcy promoted ER stress and apoptosis of hepatocytes and thereby aggravated liver injury through inhibiting ERO1α expression; accordingly, overexpression of ERO1α remarkably alleviated ER stress and apoptosis of hepatocytes induced by Hcy. Epigenetic modification analysis revealed that Hcy significantly increased levels of DNA methylation and H3 lysine 9 dimethylation (H3K9me2) on ERO1α promoter, which attributed to upregulated DNA methyltransferase 1 (DNMT1) and G9a, respectively. Further study showed that DNMT1 and G9a cooperatively regulated ERO1α expression in hepatocytes exposed to Hcy. Taken together, our work demonstrates that Hcy activates ER stress and apoptosis of hepatocytes by downregulating ERO1α expression via cooperation between DNMT1 and G9a, which provides new insight into the mechanism of Hcy‐induced ER stress and apoptosis of hepatocytes in liver injury.

Epigenetic Editing in Prostate Cancer: Challenges and Opportunities

Epigenome editing consists of fusing a predesigned DNA recognition unit to the catalytic domain of a chromatin modifying enzyme leading to the introduction or removal of an epigenetic mark at a specific locus. These platforms enabled the study of the mechanisms and roles of epigenetic changes in several research domains such as those addressing pathogenesis and progression of cancer. Despite the continued efforts required to overcome some limitations, which include specificity, off-target effects, efficacy, and longevity, these tools have been rapidly progressing and improving.Since prostate cancer is characterized by multiple genetic and epigenetic alterations that affect different signalling pathways, epigenetic editing constitutes a promising strategy to hamper cancer progression. Therefore, by modulating chromatin structure through epigenome editing, its conformation might be better understood and events that drive prostate carcinogenesis might be further unveiled.This review describes the different epigenome engineering tools, their mechanisms concerning gene's expression and regulation, highlighting the challenges and opportunities concerning prostate cancer research.

DNA hydroxymethylation increases the susceptibility of reactivation of methylated P16 alleles in cancer cells

It is well established that 5-methylcytosine (5mC) in genomic DNA of mammalian cells can be oxidized into 5-hydroxymethylcytosine (5hmC) and other derivates by DNA dioxygenase TETs. While conversion of 5mC to 5hmC plays an important role in active DNA demethylation through further oxidation steps, a certain proportion of 5hmCs remain in the genome. Although 5hmCs contribute to the flexibility of chromatin and protect bivalent promoters from hypermethylation, the direct effect of 5hmCs on gene transcription is unknown. In this present study, we have engineered a zinc-finger protein-based P16-specific DNA dioxygenase (P16-TET) to induce P16 hydroxymethylation and demethylation in cancer cells. Our results demonstrate, for the first time, that although the hydroxymethylated P16 alleles retain transcriptionally inactive, hydroxymethylation could increase the susceptibility of reactivation of methylated P16 alleles.

P16 methylation increases the sensitivity of cancer cells to the CDK4/6 inhibitor palbociclib

The P16 (CDKN2A^ink4a) gene is an endogenous CDK4/6 inhibitor. Palbociclib (PD0332991) is an anti-CDK4/6 chemical for cancer treatment. P16 is most frequently inactivated by copy number deletion and DNA methylation in cancers. It is well known that cancer cells with P16 deletion are more sensitive to palbociclib than those without. However, whether P16 methylation is related to palbociclib sensitivity is not known. By analyzing public pharmacogenomic datasets, we found that the IC50 of palbociclib in cancer cell lines (n = 522) was positively correlated with both the P16 expression level and P16 gene copy number. Our experimental results further showed that cancer cell lines with P16 methylation were more sensitive to palbociclib than those without. To determine whether P16 methylation directly increased the sensitivity of cancer cells to palbociclib, we induced P16 methylation in the lung cancer cell lines H661 and HCC827 and the gastric cancer cell line BGC823 via an engineered P16-specific DNA methyltransferase (P16-Dnmt) and found that the sensitivity of these cells to palbociclib was significantly increased. The survival rate of P16-Dnmt cells was significantly lower than that of vector control cells 48 hrs post treatment with palbociclib (10 μM). Notably, palbociclib treatment also selectively inhibited the proliferation of the P16-methylated subpopulation of P16-Dnmt cells, further indicating that P16 methylation can increase the sensitivity of cells to this CDK4/6 inhibitor. These results were confirmed in an animal experiment. In conclusion, inactivation of the P16 gene by DNA methylation can increase the sensitivity of cancer cells to palbociclib.

CRISPR/Cas9-based epigenome editing: An overview of dCas9-based tools with special emphasis on off-target activity

Molecular tools for gene regulation and epigenome editing consist of two main parts: the targeting moiety binding a specific genomic locus and the effector domain performing the editing or regulatory function. The advent of CRISPR-Cas9 technology enabled easy and flexible targeting of almost any locus by co-expression of a small sgRNA molecule, which is complementary to the target sequence and forms a complex with Cas9, directing it to that particular target. Here, we review strategies for recruitment of effector domains, used in gene regulation and epigenome editing, to the dCas9 DNA-targeting protein. To date, the most important CRISPR-Cas9 applications in gene regulation are CRISPR activation or interference, while epigenome editing focuses on targeted changes in DNA methylation and histone modifications. Several strategies for signal amplification by recruitment of multiple effector domains deserve special focus. While some approaches rely on altering the sgRNA molecule and extending it with aptamers for effector domain recruitment, others use modifications to the Cas9 protein by direct fusions with effector domains or by addition of an epitope tag, which also has the ability to bind multiple effector domains. A major barrier to the widespread use of CRISPR-Cas9 technology for therapeutic purposes is its off-target effect. We review efforts to enhance CRISPR-Cas9 specificity by selection of Cas9 orthologs from various bacterial species and their further refinement by introduction of beneficial mutations. The molecular tools available today enable a researcher to choose the best balance of targeting flexibility, activity amplification, delivery method and specificity.

Clinical and biological significance of a - 73A > C variation in the CDH1 promoter of patients with sporadic gastric carcinoma

BACKGROUND

CDH1 germline mutations lead to hereditary diffuse gastric carcinomas. However, it is unclear whether genetic variations in the CDH1 promoter affect the progression of sporadic gastric carcinomas (SGCs).

METHODS

SGC patients in two independent cohorts with follow-up data were enrolled. The CDH1 genotypes, including the - 73A > C polymorphism (rs28372783), were determined by PCR sequencing. The CDH1 promoter activity was determined using reporter assays. SNAIL bound to CDH1 alleles was determined by chromatin immunoprecipitation primer extension PCR. CDH1 DNA methylation was determined by bisulfite-based PCR analyses.

RESULTS

Kaplan-Meier analyses showed that the overall survival (OS) of the - 73C/C patients was significantly longer than that of the - 73A/C or - 73A/A patients in a Chinese cohort [n = 526; hazard ratio 0.68 (95% CI 0.47-1.00)], which was validated in an independent Korea cohort [n = 215; hazard ratio 0.49 (95% CI 0.26-0.94)]. Moreover, the transcription activity of the - 73C alleles was significantly higher than that of the - 73A alleles in vitro and in vivo. The ratio of SNAIL recruited to the promoter regions of the - 73C and - 73A alleles was 1:10, indicating a strong influence of this polymorphism on the recruitment of SNAIL to the flanking E-box. The prevalence of DNA methylation of the CpG island and shore within the promoter of the - 73C allele was much less than that of the - 73A allele in both gastric tissues and cancer cell lines.

CONCLUSION

The - 73A > C variation may lead to differences in the overall survival of SGC patients and allele-specific repressions of CDH1.

Coordinated transcription of ANRIL and P16 genes is silenced by P16 DNA methylation

Objective

To investigate the relationship between the transcription of ANRIL, P15, P14 and P16 at the same locus and the regulation mechanism of ANRIL.

Methods

Publicly available database of Cancer Cell Line Encyclopedia (CCLE) was used in bioinformatic analyses. Methylation of CpG islands was detected by denaturing high performance liquid chromatography (DHPLC). Gene transcript levels were determined using quantitative real-time polymerase chain reaction (qRT-PCR) assays. An engineered P16-specific transcription factor and DNA methyltransferase were used to induce P16-specific DNA demethylation and methylation.

Results

The expression level of ANRIL was positively and significantly correlated with that of P16 but not with that of P15 in the CCLE database. This was confirmed in human cell lines and patient colon tissue samples. In addition, ANRIL was significantly upregulated in colon cancer tissues. Transcription of ANRIL and P16 was observed only in cell lines in which the P16 alleles were unmethylated and not in cell lines with fully methylated P16 alleles. Notably, P16-specific methylation significantly decreased transcription of P16 and ANRIL in BGC823 and GES1 cells. In contrast, P16-specific demethylation re-activated transcription of ANRIL and P16 in H1299 cells (P<0.001). Alteration ofANRIL expression was not induced by P16 expression changes.

Conclusions

ANRIL and P16 are coordinately transcribed in human cells and regulated by the methylation status of the P16 CpG islands around the transcription start site.

Zinc Fingers, TALEs, and CRISPR Systems: A Comparison of Tools for Epigenome Editing

The completion of genome, epigenome, and transcriptome mapping in multiple cell types has created a demand for precision biomolecular tools that allow researchers to functionally manipulate DNA, reconfigure chromatin structure, and ultimately reshape gene expression patterns. Epigenetic editing tools provide the ability to interrogate the relationship between epigenetic modifications and gene expression. Importantly, this information can be exploited to reprogram cell fate for both basic research and therapeutic applications. Three different molecular platforms for epigenetic editing have been developed: zinc finger proteins (ZFs), transcription activator-like effectors (TALEs), and the system of Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR) and CRISPR-associated (Cas) proteins. These platforms serve as custom DNA-binding domains (DBDs), which are fused to epigenetic modifying domains to manipulate epigenetic marks at specific sites in the genome. The addition and/or removal of epigenetic modifications reconfigures local chromatin structure, with the potential to provoke long-lasting changes in gene transcription. Here we summarize the molecular structure and mechanism of action of ZF, TALE, and CRISPR platforms and describe their applications for the locus-specific manipulation of the epigenome. The advantages and disadvantages of each platform will be discussed with regard to genomic specificity, potency in regulating gene expression, and reprogramming cell phenotypes, as well as ease of design, construction, and delivery. Finally, we outline potential applications for these tools in molecular biology and biomedicine and identify possible barriers to their future clinical implementation.

Targeted silencing of SOX2 by an artificial transcription factor showed antitumor effect in lung and esophageal squamous cell carcinoma

SOX2 is a transcription factor essential for early mammalian development and for the maintenance of stem cells. Recently, SOX2 was identified as a lineage specific oncogene, recurrently amplified and activated in lung and esophageal squamous cell carcinoma (SCC). In this study, we have developed a zinc finger-based artificial transcription factor (ATF) to selectively suppress SOX2 expression in cancer cells and termed the system ATF/SOX2. We engineered the ATF using six zinc finger arrays designed to target a 19 bp site in the SOX2 distal promoter and a KOX transcriptional repressor domain. A recombinant adenoviral vector Ad-ATF/SOX2 that expresses ATF/SOX2 suppressed SOX2 at the mRNA and protein levels in lung and esophageal SCC cells expressing SOX2. In these kinds of cells, Ad-ATF/SOX2 decreased cell proliferation and colony formation more effectively than the recombinant adenoviral vector Ad-shSOX2, which expresses SOX2 short hairpin RNA (shSOX2). Ad-ATF/SOX2 induced the cell cycle inhibitor CDKN1A more strongly than Ad-shSOX2. Importantly, the ATF did not suppress the cell viability of normal human cells. Moreover, Ad-ATF/SOX2 effectively inhibited tumor growth in a lung SCC xenograft mouse model. These results indicate that ATF/SOX2 would lead to the development of an effective molecular-targeted therapy for lung and esophageal SCC.

Epigenetic Editing: On the Verge of Reprogramming Gene Expression at Will

Genome targeting has quickly developed as one of the most promising fields in science. By using programmable DNA-binding platforms and nucleases, scientists are now able to accurately edit the genome. These DNA-binding tools have recently also been applied to engineer the epigenome for gene expression modulation. Such epigenetic editing constructs have firmly demonstrated the causal role of epigenetics in instructing gene expression. Another focus of epigenome engineering is to understand the order of events of chromatin remodeling in gene expression regulation. Groundbreaking approaches in this field are beginning to yield novel insights into the function of individual chromatin marks in the context of maintaining cellular phenotype and regulating transient gene expression changes. This review focuses on recent advances in the field of epigenetic editing and highlights its promise for sustained gene expression reprogramming.

P16-specific DNA methylation by engineered zinc finger methyltransferase inactivates gene transcription and promotes cancer metastasis

Background

P16 DNA methylation is well known to be the most frequent event in cancer development. It has been reported that genetic inactivation of P16 drives cancer growth and metastasis, however, whether P16 DNA methylation is truly a driver in cancer metastasis remains unknown.

Results

A P16-specific DNA methyltransferase (P16-dnmt) expression vector is designed using a P16 promoter-specific engineered zinc finger protein fused with the catalytic domain of dnmt3a. P16-dnmt transfection significantly decreases P16 promoter activity, induces complete methylation of P16 CpG islands, and inactivates P16 transcription in the HEK293T cell line. The P16-Dnmt coding fragment is integrated into an expression controllable vector and used to induce P16-specific DNA methylation in GES-1 and BGC823 cell lines. Transwell assays show enhanced migration and invasion of these cancer cells following P16-specific DNA methylation. Such effects are not observed in the P16 mutant A549 cell line. These results are confirmed using an experimental mouse pneumonic metastasis model. Moreover, enforced overexpression of P16 in these cells reverses the migration phenotype. Increased levels of RB phosphorylation and NFκB subunit P65 expression are also seen following P16-specific methylation and might further contribute to cancer metastasis.

Conclusion

P16 methylation could directly inactivate gene transcription and drive cancer metastasis.

Electronic supplementary material

The online version of this article (doi:10.1186/s13059-015-0819-6) contains supplementary material, which is available to authorized users.

Prolonged re-expression of the hypermethylated gene EPB41L3 using artificial transcription factors and epigenetic drugs

Epigenetic silencing of tumor suppressor genes (TSGs) is considered a significant event in the progression of cancer. For example, EPB41L3, a potential biomarker in cervical cancer, is often silenced by cancer-specific promoter methylation. Artificial transcription factors (ATFs) are unique tools to re-express such silenced TSGs to functional levels; however, the induced effects are considered transient. Here, we aimed to improve the efficiency and sustainability of gene re-expression using engineered zinc fingers fused to VP64 (ZF-ATFs) or DNA methylation modifiers (ZF-Tet2 or ZF-TDG) and/or by co-treatment with epigenetic drugs [5-aza-2'-deoxycytidine or Trichostatin A (TSA)]. The EPB41L3-ZF effectively bound its methylated endogenous locus, as also confirmed by ChIP-seq. ZF-ATFs reactivated the epigenetically silenced target gene EPB41L3 (∼ 10-fold) in breast, ovarian, and cervical cancer cell lines. Prolonged high levels of EPB41L3 (∼ 150-fold) induction could be achieved by short-term co-treatment with epigenetic drugs. Interestingly, for otherwise ineffective ZF-Tet2 or ZF-TDG treatments, TSA facilitated re-expression of EPB41L3 up to twofold. ATF-mediated re-expression demonstrated a tumor suppressive role for EPB41L3 in cervical cancer cell lines. In conclusion, epigenetic reprogramming provides a novel way to improve sustainability of re-expression of epigenetically silenced promoters.

Homeostatic maintenance of allele-specific p16 methylation in cancer cells accompanied by dynamic focal methylation and hydroxymethylation

AIM

p16 Methylation frequently occurs in carcinogenesis. While it has been hypothesized that the p16 methylation states are dynamically maintained in cancer cells, direct evidence supporting this hypothesis has not been available until now.

METHODS

A fusion cell model was established which reprogrammed the native DNA methylation pattern of the cells. The methylation status of the p16 alleles was then repeatedly quantitatively analyzed in the fusion monoclonal, parental cancer cell lines (p16-completely methylated-AGS and unmethylated-MGC803), and HCT116 non-fusion cell using DHPLC and bisulfite sequencing. Histone methylation was analyzed using chromatin immuno-precipitation (ChIP)-PCR. P16 expression status was determined using immuno-staining and RT-PCR.

RESULTS

The methylation status for the majority of the p16 alleles was stably maintained in the fusion monoclonal cells after up to 60 passages. Most importantly, focal de novo methylation, demethylation, and hydroxymethylation were consistently observed within about 27% of the p16 alleles in the fusion monoclones, but not the homozygously methylated or unmethylated parental cells. Furthermore, subclones of the monoclones consistently maintained the same p16 methylation pattern. A similar phenomenon was also observed using the p16 hemi-methylated HCT116 non-fusion cancer cell line. Interestingly, transcription was not observed in p16 alleles that were hydroxymethylated with an antisense-strand-specific pattern. Also, the levels of H3K9 and H3K4 trimethylation in the fusion cells were found to be slightly lower than the parental AGS and MGC803 cells, respectively.

CONCLUSION

The present study provides the first direct evidence confirming that the methylation states of p16 CpG islands is not only homeostatically maintained, but also accompanied by a dynamic process of transient focal methylation, demethylation, and hydroxymethylation in cancer cells.

miR-219-1-3p is a negative regulator of the mucin MUC4 expression and is a tumor suppressor in pancreatic cancer

Pancreatic ductal adenocarcinoma (PDAC) is among the most lethal cancers in the world with one of the worst outcome. The oncogenic mucin MUC4 has been identified as an actor of pancreatic carcinogenesis as it is involved in many processes regulating pancreatic cancer cell biology. MUC4 is not expressed in healthy pancreas whereas it is expressed very early in pancreatic carcinogenesis. Targeting MUC4 in these early steps may thus appear as a promising strategy to slow-down pancreatic tumorigenesis. miRNA negative regulation of MUC4 could be one mechanism to efficiently downregulate MUC4 gene expression in early pancreatic neoplastic lesions. Using in silico studies, we found two putative binding sites for miR-219-1-3p in the 3'-UTR of MUC4 and showed that miR-219-1-3p expression is downregulated both in PDAC-derived cell lines and human PDAC tissues compared with their normal counterparts. We then showed that miR-219-1-3p negatively regulates MUC4 mucin expression via its direct binding to MUC4 3'-UTR. MiR-219-1-3p overexpression (transient and stable) in pancreatic cancer cell lines induced a decrease of cell proliferation associated with a decrease of cyclin D1 and a decrease of Akt and Erk pathway activation. MiR-219-1-3p overexpression also decreased cell migration. Furthermore, miR-219-1-3p expression was found to be conversely correlated with Muc4 expression in early pancreatic intraepithelial neoplasia lesions of Pdx1-Cre;LSL-Kras(G12D) mice. Most interestingly, in vivo studies showed that miR-219-1-3p injection in xenografted pancreatic tumors in mice decreased both tumor growth and MUC4 mucin expression. Altogether, these results identify miR-219-1-3p as a new negative regulator of MUC4 oncomucin that possesses tumor-suppressor activity in PDAC.

C-terminal in Sp1-like artificial zinc-finger proteins plays crucial roles in determining their DNA binding affinity

Background

It is well known that the C-terminal zinc-finger-3 in transcription factor Sp1 contributes more than the N-terminal zinc-finger-1 in determining Sp1’s DNA binding capacity. Sp1-like artificial poly-zinc-finger proteins (ZFPs) are powerful biotechnological tools for gene-specific recognization and manipulation. It is important to understand whether the C-terminal fingers in the Sp1-like artificial ZFPs remain crucial for their DNA binding ability. Recently, a set of p16 promoter-specific seven-ZFPs (7ZFPs) has been constructed to reactivate the expression of methylation-silenced p16. These 7ZFPs contain one N-terminal three-zinc-finger domain of Sp1 (3ZF), two Sp1-like two-zinc-finger domains derived from the Sp1 finger-2 and finger-3 (2ZF) in the middle and C-terminal regions.

Results

In the present study, sets of variants for several representative 7ZFPs with the p16-binding affinity were further constructed. This was accomplished through finger replacements and key amino acid mutations in the N-terminal fingers, C-terminal fingers, and linker peptide, respectively. Their p16-binding activity was analysed using gel mobility shift assays. Results showed that the motif replacement or a key amino acid mutation (S > R) at position +2 of the α-helix in the C-terminal 2ZF domain completely abolished their p16-binding affinity. Deletion of three amino acids in a consensus linker (TGEKP > TG) between finger-7 and the 6 × Histidine-tag in the C-terminal also dramatically abolished their binding affinity. In contrast, the replacement of the finger-3 in the N-terminal 3ZF domain did not affect their binding affinity, but decreased their binding stability.

Conclusions

Altogether, the present study show that the C-terminal region may play crucial roles in determining the DNA binding affinity of Sp1-like artificial ZFPs.

Functional validation of putative tumor suppressor gene C13ORF18 in cervical cancer by Artificial Transcription Factors

C13ORF18 is frequently hypermethylated in cervical cancer but not in normal cervix and might serve as a biomarker for the early detection of cervical cancer in scrapings. As hypermethylation is often observed for silenced tumor suppressor genes (TSGs), hypermethylated biomarker genes might exhibit tumor suppressive activities upon re-expression. Epigenetic drugs are successfully exploited to reverse TSG silencing, but act genome-wide. Artificial Transcription Factors (ATFs) provide a gene-specific approach for re-expression of silenced genes. Here, we investigated the potential tumor suppressive role of C13ORF18 in cervical cancer by ATF-induced re-expression. Five zinc finger proteins were engineered to bind the C13ORF18 promoter and fused to a strong transcriptional activator. C13ORF18 expression could be induced in cervical cell lines: ranging from >40-fold in positive (C13ORF18-unmethylated) cells to >110-fold in negative (C13ORF18-methylated) cells. Re-activation of C13ORF18 resulted in significant cell growth inhibition and/or induction of apoptosis. Co-treatment of cell lines with ATFs and epigenetic drugs further enhanced the ATF-induced effects. Interestingly, re-activation of C13ORF18 led to partial demethylation of the C13ORF18 promoter and decreased repressive histone methylation. These data demonstrate the potency of ATFs to re-express and potentially demethylate hypermethylated silenced genes. Concluding, we show that C13ORF18 has a TSG function in cervical cancer and may serve as a therapeutic anti-cancer target. As the amount of epimutations in cancer exceeds the number of gene mutations, ATFs provide promising tools to validate hypermethylated marker genes as therapeutic targets.