Promoter methylation of helicase-like transcription factor is associated with the early stages of gastric cancer with family history

The fork remodeler helicase-like transcription factor in cancer development: all at once

The Helicase-like Transcription Factor (HLTF) is a member of the SNF2-family of fork remodelers, primarily studied for its capacity to provide DNA Damage Tolerance (DDT) and to induce replication fork reversal (RFR). HLTF is recruited at stalled forks where both its ATPase motor and HIP116 Rad5p N-terminal (HIRAN) domains are necessary for regulating its interaction with DNA. HIRAN bestows specificity to ssDNA 3'-end and imparts branch migration as well as DNA remodeling capabilities facilitating damage repair. Both expression regulation and mutation rate affect HLTF activity. Gene hypermethylation induces loss of HLTF function, in particular in colorectal cancer (CRC), implying a tumour suppressor role. Surprisingly, a correlation between hypermethylation and HLTF mRNA upregulation has also been observed, even within the same cancer type. In many cancers, both complex mutation patterns and the presence of gene Copy Number Variations (CNVs) have been reported. These conditions affect the amount of functional HLTF and question the physiological role of this fork remodeler. This review offers a systematic collection of the presently strewed information regarding HLTF, its structural and functional characteristics, the multiple roles in DDT and the regulation in cancer progression highlighting new research perspectives.

HLTF/SERPINE1 Axis Plays a Crucial Pro-Oncogenic Role in the Progression from Cervical Precancerous Lesions to Cervical Carcinoma in vitro

OBJECTIVES

Cervical carcinoma (CC) is prevalent among women worldwide with increasing risk. Finding effective methods for treating CC is of utmost importance. The aim of this study was to investigate the effect of SERPINE1 on the progression of cervical precancerous lesions to CC.

DESIGN

This study used transcriptome sequencing and in vitro cell line. Participants/Materials: Cervical precancerous lesions and CC samples and human cervical epithelial immortalized cell line H8, human CC cell lines HeLa, and CaSki were involved in this study.

SETTING AND METHODS

Next-generation sequencing was applied to identify 100 differentially expressed genes from cervical precancerous lesions and CC samples. With the application of the Search Tool for the Retrieval of Interacting Genes (STRING) database, we carried out the protein-protein interaction network analysis, thus screening out serine protease inhibitor clade E member 1 (SERPINE1) with significant upregulation in CC cells. The helicase-like transcription factor (HLTF) was predicted as the upstream transcription factor using Human Transcription Factor Database (HumanTFDB). The chromatin immunoprecipitation (ChIP) experiment was conducted to validate the interaction between SERPINE1 and HLTF. The immunohistochemistry was employed to determine the expression of SERPINE1 and HLTF in CC tissues. Following the upregulation or downregulation of SERPINE1 and HLTF, the real-time quantitative reverse transcription polymerase chain reaction was carried out to assess mRNA expression levels of SERPINE1 and HLTF in cells. Cell viability, migration, and invasion were evaluated using MTT assay, cell scratch assay, and Transwell assay, respectively. Western blot analysis was conducted to assess changes in the expression levels of matrix metalloproteinases and proteins related to epithelial-mesenchymal transition (EMT).

RESULTS

The ChIP experiment confirmed the interaction between HLTF and SERPINE1. HLTF and SERPINE1 were upregulated in CC tissues and cells, and silencing SERPINE1 inhibited the EMT process and viability, migration, and invasion of CC cells. However, overexpression of SERPINE1 in CC cells showed the opposite trend. Rescue experiments demonstrated that silencing HLTF repressed CC cell viability, migration, and invasion, which could be restored by overexpressing SERPINE1.

LIMITATIONS

The effect of the HLTF/SERPINE1 axis on CC malignant progression has not been confirmed by in vivo experiments.

CONCLUSION

HLTF transcriptionally activates SERPINE1, promoting the progression from cervical precancerous lesions to CC.

Galectin-7 Induction by EHMT2 Inhibition Enhances Immunity in Microsatellite Stability Colorectal Cancer

BACKGROUND & AIMS

Although immunotherapy shows substantial advancement in colorectal cancer (CRC) with microsatellite instability high, it has limited efficacy for CRC with microsatellite stability (MSS). Identifying combinations that reverse immune suppression and prime MSS tumors for current immunotherapy approaches remains an urgent need.

METHODS

An in vitro CRISPR screen was performed using coculture models of primary tumor cells and autologous immune cells from MSS CRC patients to identify epigenetic targets that could enhance immunotherapy efficacy in MSS tumors.

RESULTS

We revealed EHMT2, a histone methyltransferase, as a potential target for MSS CRC. EHMT2 inhibition transformed the immunosuppressive microenvironment of MSS tumors into an immunomodulatory one by altering cytokine expression, leading to T-cell-mediated cytotoxicity activation and improved responsiveness to anti-PD1 treatment. We observed galectin-7 up-regulation upon EHMT2 inhibition, which converted a "cold" MSS tumor environment into a T-cell-inflamed one. Mechanistically, CHD4 repressed galectin-7 expression by recruiting EHMT2 to form a cotranscriptional silencing complex. Galectin-7 administration enhanced anti-PD1 efficacy in MSS CRC, serving as a potent adjunct cytokine therapy.

CONCLUSIONS

Our findings suggest that targeting the EHMT2/galectin-7 axis could provide a novel combination strategy for immunotherapy in MSS CRC.

Multi-omics Combined with Machine Learning Facilitating the Diagnosis of Gastric Cancer

Gastric cancer (GC) is a highly intricate gastrointestinal malignancy. Early detection of gastric cancer forms the cornerstone of precision medicine. Several studies have been conducted to investigate early biomarkers of gastric cancer using genomics, transcriptomics, proteomics, and metabolomics, respectively. However, endogenous substances associated with various omics are concurrently altered during gastric cancer development. Furthermore, environmental exposures and family history can also induce modifications in endogenous substances. Therefore, in this study, we primarily investigated alterations in DNA mutation, DNA methylation, mRNA, lncRNA, miRNA, circRNA, and protein, as well as glucose, amino acid, nucleotide, and lipid metabolism levels in the context of GC development, employing genomics, transcriptomics, proteomics, and metabolomics. Additionally, we elucidate the impact of exposure factors, including HP, EBV, nitrosamines, smoking, alcohol consumption, and family history, on diagnostic biomarkers of gastric cancer. Lastly, we provide a summary of the application of machine learning in integrating multi-omics data. Thus, this review aims to elucidate: i) the biomarkers of gastric cancer related to genomics, transcriptomics, proteomics, and metabolomics; ii) the influence of environmental exposure and family history on multiomics data; iii) the integrated analysis of multi-omics data using machine learning techniques.

HLTF promotes hepatocellular carcinoma progression by enhancing SRSF1 stability and activating ERK/MAPK pathway

Helicase-like transcription factor (HLTF) has been found to be involved in the progression of several tumors, but the role of HLTF in hepatocellular carcinoma (HCC) progression has not been studied. Here, our study explored the underlying mechanism of HLTF in HCC progression for the first time. Database analysis and clinical sample examination indicated that HLTF was upregulated in HCC tissues and was related to poor clinicopathological features in patients. Upregulation of HLTF accelerated the growth and metastasis of HCC cells both in vitro and in vivo. Bioinformatics analysis and subsequent experiments revealed that ERK/MAPK signaling pathway activation was vital to HLTF-mediated proliferation and metastasis in HCC cells. Moreover, HLTF was demonstrated to interact with SRSF1 and contribute to its protein stability to activate the ERK/MAPK signaling pathway and enhance HCC growth and metastasis. In addition, miR-511-5p was expressed at a low level in HCC tissues, was negatively correlated HLTF, and regulated HLTF expression. Our study shows that HLTF plays an oncogenic role in HCC progression and provides a novel biomarker and therapeutic target for the diagnosis and treatment of HCC.

DNA Sequence Specificity Reveals a Role of the HLTF HIRAN Domain in the Recognition of Trinucleotide Repeats

DNA damage tolerance (DDT) pathways enable cells to cope with a variety of replication blocks that threaten their ability to complete DNA replication. Helicase-like transcription factor (HLTF) plays a central role in the error-free DDT pathway, template switching (TS), by serving as a ubiquitin ligase to polyubiquitinate the DNA sliding clamp PCNA, which promotes TS initiation. HLTF also serves as an ATP-dependent DNA translocase facilitating replication fork remodeling. The HIP116, Rad5p N-terminal (HIRAN) domain of HLTF specifically recognizes the unmodified 3'-end of single-stranded DNA (ssDNA) at stalled replication forks to promote fork regression. Several crystal structures of the HIRAN domain in complex with ssDNA have been reported; however, optimal ssDNA sequences for high-affinity binding with the domain have not been described. Here we elucidated DNA sequence preferences of HLTF HIRAN through systematic studies of its binding to ssDNA substrates using fluorescence polarization assays and a computational analysis of the ssDNA:HIRAN interaction. These studies reveal that the HLTF HIRAN domain preferentially recognizes a (T/C)TG sequence at the 3'-hydroxyl ssDNA end, which occurs in the CTG trinucleotide repeat (TNR) regions that are susceptible to expansion and deletion mutations identified in neuromuscular and neurodegenerative disorders. These findings support a role for HLTF in maintaining the stability of difficult to replicate TNR microsatellite regions.

Ankylosing Spondylitis Patients Display Aberrant ERAP1 Gene DNA Methylation and Expression

BACKGROUND

Endoplasmic reticulum aminopeptidase 1 (ERAP1) is known to participate in the pathogenesis of ankylosing spondylitis (AS). This study aimed to evaluate the relationship between promoter methylation and mRNA levels of ERAP1 and AS susceptibility.

METHODS

DNA methylation levels of 100 AS patients and 100 healthy controls (HCs) were tested using a targeted bisulfite sequencing assay. To verify the results of DNA methylation, mRNA levels of ERAP1 were measured in 20 AS patients and HCs used quantitative real-time reverse transcription-polymerase chain reaction.

RESULTS

The DNA methylation levels of two CpG islands containing 31 loci in ERAP1 promoter were measured. ERAP1_1 (P< .001) and ERAP1_2 (P< .001) islands were significantly hypermethylated in AS patients compared with HCs. In the verification study, the mRNA levels of ERAP1 were significantly decreased in AS patients. The ROC curve analysis showed that the sensitivity, specificity and area under curve were 0.717, 0.737, and 0.779 of differential methylated CpG loci of ERAP1 for AS diagnosis. In AS patients, the methylation levels of EARP1 were associated with family history, non-steroidal anti-inflammatory drugs use, X-ray classification, and clinical manifestations.

CONCLUSIONS

Our study demonstrated that the ERAP1 gene is significantly hypermethylated, and mRNA levels of EARP1 decreased, in AS patients. Our findings suggested that the aberrant methylation of ERAP1 promoter may be involved in the pathogenesis of AS and could be considered as a diagnostic tool and therapeutic target of AS.Abbreviations AS: Ankylosing Spondylitis; AUC: Area Under Curve; BASDAI: Bath Ankylosing Spondylitis Disease Activity Index; BASFI: Bath Ankylosing Spondylitis Functional Index; CI: Confidence Interval; CpG: Cytosine-guanine Dinucleotide; CRP: C-reactive Protein; ERAP1: Endoplasmic Reticulum Aminopeptidase 1; ESR: Erythrocyte Sedimentation Rate; EWAS: Epigenome-Wide Association Study; HLA: Human Leukocyte Antigen; OR: Odds Ratio; PCR: Polymerase Chain Reaction; ROC: Receiver Operating Characteristic; NSAIDs: Non-Steroidal Anti-Inflammatory Drugs.

Promising aberrant DNA methylation marker to predict gastric cancer development in individuals with family history and long-term effects of H. pylori eradication on DNA methylation

OBJECTIVE

It remains unknown whether individuals with a family history (FH) of gastric cancer (GC) are associated with aberrant DNA methylation. The aim of this study was to investigate the association between aberrant DNA methylation and FH of GC.

DESIGN

Using quantitative MethyLight assay, MOS, miR124a-3, NKX6-1, EMX1, CDH1, and TWIST1 methylation levels in the noncancerous gastric mucosa was compared between subjects with and without FH based on GC and Helicobacter pylori (Hp) infection. Changes in the methylation levels were evaluated over time after Hp eradication.

RESULTS

In Hp-positive GC patients, MOS (P < 0.001), CDH1 (P < 0.001), and TWIST1 (P = 0.004) methylation were decreased in subjects with FH (n = 64) than in those without FH (n = 58). In Hp-positive controls, MOS methylation was lower in subjects with FH (n = 73) than in those without FH (n = 50) (P = 0.042), while miR124a-3 (P = 0.006), NKX6-1 (P < 0.001), and CDH1 (P < 0.001) methylation were higher in subjects with FH. CDH1 methylation constantly decreased from 2 years in GC patients and 3-4 years in controls after Hp eradication (all P < 0.001). A persistent decrease in methylation over time was not observed in other genes after eradication.

CONCLUSION

The methylation of MOS and CDH1 provided an association between aberrant DNA methylation and gastric carcinogenesis in FH of GC, a useful marker for GC risk in individuals with FH. Furthermore, CDH1 methylation decreased after Hp eradication.

The Human RAD5 Homologs, HLTF and SHPRH, Have Separate Functions in DNA Damage Tolerance Dependent on The DNA Lesion Type

Helicase-like transcription factor (HLTF) and SNF2, histone-linker, PHD and RING finger domain-containing helicase (SHPRH), the two human homologs of yeast Rad5, are believed to have a vital role in DNA damage tolerance (DDT). Here we show that HLTF, SHPRH and HLTF/SHPRH knockout cell lines show different sensitivities towards UV-irradiation, methyl methanesulfonate (MMS), cisplatin and mitomycin C (MMC), which are drugs that induce different types of DNA lesions. In general, the HLTF/SHPRH double knockout cell line was less sensitive than the single knockouts in response to all drugs, and interestingly, especially to MMS and cisplatin. Using the SupF assay, we detected an increase in the mutation frequency in HLTF knockout cells both after UV- and MMS-induced DNA lesions, while we detected a decrease in mutation frequency over UV lesions in the HLTF/SHPRH double knockout cells. No change in the mutation frequency was detected in the HLTF/SHPRH double knockout cell line after MMS treatment, even though these cells were more resistant to MMS and grew faster than the other cell lines after treatment with DNA damaging agents. This phenotype could possibly be explained by a reduced activation of checkpoint kinase 2 (CHK2) and MCM2 (a component of the pre-replication complex) after MMS treatment in cells lacking SHPRH. Our data reveal both distinct and common roles of the human RAD5 homologs dependent on the nature of DNA lesions, and identified SHPRH as a regulator of CHK2, a central player in DNA damage response.

Helicase-Like Transcription Factor HLTF and E3 Ubiquitin Ligase SHPRH Confer DNA Damage Tolerance through Direct Interactions with Proliferating Cell Nuclear Antigen (PCNA)

To prevent replication fork collapse and genome instability under replicative stress, DNA damage tolerance (DDT) mechanisms have evolved. The RAD5 homologs, HLTF (helicase-like transcription factor) and SHPRH (SNF2, histone-linker, PHD and RING finger domain-containing helicase), both ubiquitin ligases, are involved in several DDT mechanisms; DNA translesion synthesis (TLS), fork reversal/remodeling and template switch (TS). Here we show that these two human RAD5 homologs contain functional APIM PCNA interacting motifs. Our results show that both the role of HLTF in TLS in HLTF overexpressing cells, and nuclear localization of SHPRH, are dependent on interaction of HLTF and SHPRH with PCNA. Additionally, we detected multiple changes in the mutation spectra when APIM in overexpressed HLTF or SHPRH were mutated compared to overexpressed wild type proteins. In plasmids from cells overexpressing the APIM mutant version of HLTF, we observed a decrease in C to T transitions, the most common mutation caused by UV irradiation, and an increase in mutations on the transcribed strand. These results strongly suggest that direct binding of HLTF and SHPRH to PCNA is vital for their function in DDT.

HLTF suppresses the migration and invasion of colorectal cancer cells via TGF‑β/SMAD signaling in vitro

Helicase‑like transcription factor (HLTF) has been identified as a tumor suppressor gene. The hypermethylation of HTLF is frequently observed in various types of cancer, including colorectal cancer (CRC). However, the mechanisms through which HLTF suppresses CRC progression remain unclear. Thus, the aim of the present study was to explore the biological function of HLTF in CRC cells and the underlying mechanisms. CRC tissues and cells were used to detect the expression of HLTF. Wound‑healing and Transwell assays were performed to assess the motility of CRC cells. The results revealed that HLTF expression was significantly associated with the differentiation status, invasion depth, lymph node metastasis and distant metastasis. A low HLTF expression was significantly associated with a poor survival. Furthermore, HTLF knockdown or ectopic overexpression significantly promoted or suppressed the motility of CRC cells, respectively. With regard to the underlying molecular mechanisms, the protein expression of HTLF was upregulated when the CRC cells were stimulated with transforming growth factor (TGF)‑β, and HLTF upregulation induced an increase in SMAD4 and p‑SMAD2/3 expression and a decrease in levels of the TGF‑β/SMAD pathway downstream genes, Vimentin and zinc finger e‑box binding homeobox 1 (ZEB1). On the whole, the findings of this study suggest that HLTF is negatively associated with the progression of CRC, and its overexpression suppresses the migration and invasion of CRC cells by targeting the TGF‑β/SMAD pathway.

Early detection of gastric cancer using global, genome-wide and IRF4, ELMO1, CLIP4 and MSC DNA methylation in endoscopic biopsies

Clinically useful molecular tools to triage gastric cancer patients are not currently available. We aimed to develop a molecular tool to predict gastric cancer risk in endoscopy-driven biopsies obtained from high-risk gastric cancer clinics in low resource settings.

We discovered and validated a DNA methylation biomarker panel in endoscopic samples obtained from 362 patients seen between 2004 and 2009 in three high-risk gastric cancer clinics in Lima, Perú, and validated it in 306 samples from the Cancer Genome Atlas project (“TCGA”). Global, epigenome wide and gene-specific DNA methylation analyses were used in a Phase I Biomarker Development Trial to identify a continuous biomarker panel that combines a Global DNA Methylation Index (GDMI) and promoter DNA methylation levels of IRF4, ELMO1, CLIP4 and MSC.

We observed an inverse association between the GDMI and histological progression to gastric cancer, when comparing gastritis patients without metaplasia (mean = 5.74, 95% CI, 4.97−6.50), gastritis patients with metaplasia (mean = 4.81, 95% CI, 3.77−5.84), and gastric cancer cases (mean = 3.38, 95% CI, 2.82−3.94), respectively (p < 0.0001). Promoter methylation of IRF4 (p < 0.0001), ELMO1 (p < 0.0001), CLIP4 (p < 0.0001), and MSC (p < 0.0001), is also associated with increasing severity from gastritis with no metaplasia to gastritis with metaplasia and gastric cancer.

Our findings suggest that IRF4, ELMO1, CLIP4 and MSC promoter methylation coupled with a GDMI>4 are useful molecular tools for gastric cancer risk stratification in endoscopic biopsies.

HIV-1 Vpr degrades the HLTF DNA translocase in T cells and macrophages

Viruses often interfere with the DNA damage response to better replicate in their hosts. The human immunodeficiency virus 1 (HIV-1) viral protein R (Vpr) protein has been reported to modulate the activity of the DNA repair structure-specific endonuclease subunit (SLX4) complex and to promote cell cycle arrest. Vpr also interferes with the base-excision repair pathway by antagonizing the uracil DNA glycosylase (Ung2) enzyme. Using an unbiased quantitative proteomic screen, we report that Vpr down-regulates helicase-like transcription factor (HLTF), a DNA translocase involved in the repair of damaged replication forks. Vpr subverts the DDB1-cullin4-associated-factor 1 (DCAF1) adaptor of the Cul4A ubiquitin ligase to trigger proteasomal degradation of HLTF. This event takes place rapidly after Vpr delivery to cells, before and independently of Vpr-mediated G2 arrest. HLTF is degraded in lymphocytic cells and macrophages infected with Vpr-expressing HIV-1. Our results reveal a previously unidentified strategy for HIV-1 to antagonize DNA repair in host cells.

The helicase-like transcription factor (HLTF) in cancer: loss of function or oncomorphic conversion of a tumor suppressor?

The Helicase-like Transcription Factor (HLTF) belongs to the SWI/SNF family of proteins involved in chromatin remodeling. In addition to its role in gene transcription, HLTF has been implicated in DNA repair, which suggests that this protein acts as a tumor suppressor. Accumulating evidence indicates that HLTF expression is altered in various cancers via two mechanisms: gene silencing through promoter hypermethylation or alternative mRNA splicing, which leads to the expression of truncated proteins that lack DNA repair domains. In either case, the alteration of HLTF expression in cancer has a poor prognosis. In this review, we gathered published clinical and molecular data on HLTF. Our purposes are (a) to address whether HLTF alterations could be considered as cancer drivers or passengers and (b) to determine whether its different functions (transcription or DNA repair) could be diverted in clonal selection during cancer progression.

Strand invasion by HLTF as a mechanism for template switch in fork rescue

Stalling of replication forks at unrepaired DNA lesions can result in discontinuities opposite the damage in the newly synthesized DNA strand. Translesion synthesis or facilitating the copy from the newly synthesized strand of the sister duplex by template switching can overcome such discontinuities. During template switch, a new primer–template junction has to be formed and two mechanisms, including replication fork reversal and D-loop formation have been suggested. Genetic evidence indicates a major role for yeast Rad5 in template switch and that both Rad5 and its human orthologue, Helicase-like transcription factor (HLTF), a potential tumour suppressor can facilitate replication fork reversal. This study demonstrates the ability of HLTF and Rad5 to form a D-loop without requiring ATP binding and/or hydrolysis. We also show that this strand-pairing activity is independent of RAD51 in vitro and is not mechanistically related to that of another member of the SWI/SNF family, RAD54. In addition, the 3′-end of the invading strand in the D-loop can serve as a primer and is extended by DNA polymerase. Our data indicate that HLTF is involved in a RAD51-independent D-loop branch of template switch pathway that can promote repair of gaps formed during replication of damaged DNA.

Chromatin regulators with tumor suppressor properties and their alterations in human cancers

Key components of the cell epigenome include DNA CpG methylation profile and chromatin modification patterns. Chromatin regulators act as master controllers of gene transcription in normal cells through regulation of histone modifications and chromatin remodeling. During human cancer pathogenesis, the functions of chromatin regulators are frequently disrupted by genetic mutations and/or epigenetic alterations, causing perturbation of broad or even genome-wide scale gene-expression profiles. Thus, histone-modifying and chromatin-remodeling genes can be taken as critical 'cancer genes'. This review summarizes the current knowledge on chromatin regulators with tumor suppressor properties, as well as their aberrant alterations in human cancers.

Loss of heterozygosity and methylation of multiple tumor suppressor genes on chromosome 3 in hepatocellular carcinoma

BACKGROUND

Genetic and epigenetic alterations are the two key mechanisms in the development of hepatocellular carcinoma (HCC). However, how they contribute to hepatocarcinogenesis and the correlation between them has not been fully elucidated.

METHODS

A total of 48 paired HCCs and noncancerous tissues were used to detect loss of heterozygosity (LOH) and the methylation profiles of five tumor suppressor genes (RASSF1A, BLU, FHIT, CRBP1, and HLTF) on chromosome 3 by using polymerase chain reaction (PCR) and methylation-specific PCR. Gene expression was analyzed by immunohistochemistry and reverse transcription (RT)-PCR.

RESULTS

Sixteen of 48 (33.3 %) HCCs had LOH on at least one locus on chromosome 3, and two smallest common deleted regions (3p22.3-24.3 and 3p12.3-14.2) were identified. RASSF1A, BLU, and FHIT showed very high frequencies of methylation in HCCs (100, 81.3, and 64.6 %, respectively) and noncancerous tissues, but not in liver tissues from control patients. Well-differentiated HCCs showed high methylation frequencies of these genes but very low frequencies of LOH. Furthermore, BLU methylation was associated with an increased level of alpha-fetoprotein, and FHIT methylation was inversely correlated with HCC recurrence. In comparison, CRBP1 showed moderate frequencies of methylation, while HLTF showed low frequencies of methylation, and CRBP1 methylation occurred mainly in elderly patients. Treatment with 5-aza-2'-deoxycytidine demethylated at least one of these genes and restored their expression in a DNA methylation-dependent or -independent manner.

CONCLUSIONS

Hypermethylation of RASSF1A, BLU, and FHIT is a common and very early event in hepatocarcinogenesis; CRBP1 methylation may also be involved in the later stage. Although LOH was not too frequent on chromosome 3, it may play a role as another mechanism in hepatocarcinogenesis.

USP7 regulates the stability and function of HLTF through deubiquitination

Human helicase-like transcription factor (HLTF) is a functional homologue of yeast Rad5 that regulates error-free replication through DNA lesions. HLTF promotes the Lys-63-linked polyubiquitination of proliferating cell nuclear antigen (PCNA) that is required for maintaining genomic stability. Here, we identified the deubiquitylating enzyme ubiquitin-specific protease 7 (USP7) as a novel regulator of HLTF stability. We found that USP7 interacted with and stabilized HLTF after genotoxic stress. Furthermore, USP7 mediated deubiquitination significantly prolonged the half-life of HLTF, which in turn increased PCNA polyubiquitination. More intriguingly, silencing of USP7 rendered A549 cells highly sensitive to DNA damage and over-expression of HLTF attenuated this sensitivity. Thus, our results delineate a previously unknown USP7-HLTF-PCNA molecular network controlling DNA damage response.

Loss of HLTF function promotes intestinal carcinogenesis

Background

HLTF (Helicase-like Transcription Factor) is a DNA helicase protein homologous to the SWI/SNF family involved in the maintenance of genomic stability and the regulation of gene expression. HLTF has also been found to be frequently inactivated by promoter hypermethylation in human colon cancers. Whether this epigenetic event is required for intestinal carcinogenesis is unknown.

Results

To address the role of loss of HLTF function in the development of intestinal cancer, we generated Hltf deficient mice. These mutant mice showed normal development, and did not develop intestinal tumors, indicating that loss of Hltf function by itself is insufficient to induce the formation of intestinal cancer. On the Apc^min/+ mutant background, Hltf^- deficiency was found to significantly increase the formation of intestinal adenocarcinoma and colon cancers. Cytogenetic analysis of colon tumor cells from Hltf ^-/-/Apc^min/+ mice revealed a high incidence of gross chromosomal instabilities, including Robertsonian fusions, chromosomal fragments and aneuploidy. None of these genetic alterations were observed in the colon tumor cells derived from Apc^min/+ mice. Increased tumor growth and genomic instability was also demonstrated in HCT116 human colon cancer cells in which HLTF expression was significantly decreased.

Conclusion

Taken together, our results demonstrate that loss of HLTF function promotes the malignant transformation of intestinal or colonic adenomas to carcinomas by inducing genomic instability. Our findings highly suggest that epigenetic inactivation of HLTF, as found in most human colon cancers, could play an important role in the progression of colon tumors to malignant cancer.

Aberrant methylation of the CpG island of HLTF gene in gastric cardia adenocarcinoma and dysplasia

OBJECTIVES

To investigate the promoter methylation of HLTF in the tissues and plasma of patients with gastric cardia adenocarcinoma (GCA) and dysplasia.

DESIGN AND METHODS

Nested MSP approach was used to detect HLTF methylation status.

RESULTS

The frequency of HLTF methylation in high grade dysplasia and GCA tumor tissues was significantly higher than that in chronic inflammation tissues and was significantly associated with upper gastrointestinal cancers (UGIC) family history and protein and mRNA expression of the gene. HLTF methylation was not found in the plasma of patients with chronic inflammation and low grade dysplasia, while 4.0% (1/25) of patients with high grade dysplasia and 20.8% of (20/96) GCA patients were detected with hypermethylation of HLTF in the plasma.

CONCLUSIONS

In all, HLTF methylation may exist in gastric cardia dysplasia stages and may play important role in the development of GCA especially in individuals with UGIC family history.

Helicase-like transcription factor confers radiation resistance in cervical cancer through enhancing the DNA damage repair capacity

Helicase-like transcription factor (HLTF) is a member of the SWI/SNF (mating type switching/sucrose non-fermenting) family of ATPases/helicases and also has a RING-finger motif characteristic of ubiquitin ligase proteins. These features have led to suggestions that HLTF functions like yeast Rad5, which promotes replication through DNA lesions via a post-replication repair pathway. However, the function of HLTF in higher eukaryotes is still unknown. Herein, we found the overexpression of HLTF in radiation recurrent human uterine cervical carcinoma tissues when compared to disease free survived patients tissues. In this study, we used RNA interference techniques to investigate the potential function of HLTF in cervical cancer cell line HeLa and found that the cell proliferation was reduced by knockdown (KD) of HLTF. A host-cell reactivation assay showed that the capacity for repair to DNA damage induced by X-ray irradiation was reduced in HLTF KD cells. X-rays also increased apoptosis in HLTF KD cells. These results suggest that HLTF is involved in DNA repair and apoptosis in cancer cells, which might represent a target for gene therapies of human cancer.

The helicase-like transcription factor is a strong predictor of recurrence in hypopharyngeal but not in laryngeal squamous cell carcinomas

AIMS

To examine the immunohistochemical expression of helicase-like transcription factor (HLTF) in relation to the prognosis of hypopharyngeal (HSCCs) and laryngeal (LSCCs) squamous cell carcinomas, and to characterize the HLTF protein variants expressed in biopsy specimens of head and neck squamous cell carcinoma (HNSCC) as well as the HeLa cell line.

METHODS AND RESULTS

HLTF expression was determined by immunohistochemistry on a series of 100 hypopharyngeal (stage IV) and 56 laryngeal SCCs (stages I, II and IV). The HLTF variants were defined using reverse transcriptase-polymerase chain reaction and Western blots in 13 fresh HNSCC biopsies and in HeLa cells. High levels of HLTF expression were associated with rapid recurrence rates in a subgroup of 81 stage IV hypopharyngeal SCCs (with complete follow-up). A 95-kDa HLTF variant truncated at the carboxyl-terminal domain was detected in addition to the 115-kDa full-size protein in HNSCC biopsies, while six variants were observed in HeLa cells.

CONCLUSIONS

Our results demonstrate, for the first time, that hypopharyngeal SCCs presenting high levels of HLTF have a worse prognosis. The quantitative determination of HLTF in hypopharyngeal SCCs was an independent prognostic marker alongside tumour node metastasis staging. HNSCCs expressed the truncated HLTF variant lacking the domains involved in DNA repair.

Association of the SUV39H1 histone methyltransferase with the DNA methyltransferase 1 at mRNA expression level in primary colorectal cancer

This study was aimed at investigating the involvement of the SUV39H1 histone methyltransferase on the epigenetic change of euchromatic promoter in colorectal cancer. We retrospectively analyzed the mRNA levels of SUV39H1 and the promoter methylation of the p14(ARF), p16(INK4a) and HLTF genes as well as the mRNA levels of DNA methyltransferase 1 (DNMT1) in fresh frozen tissues from 219 colorectal cancer patients. The mRNA levels of the SUV39H1 and DNMT1 were assessed via quantitative real-time PCR and the methylation profiles of the CpG islands were determined using methylation-specific PCR. The mRNA levels of SUV39H1 and DNMT1 were elevated in 25% and 42% of 219 colorectal cancers, respectively. The hypermethylation of the p14(ARF), p16(INK4a) and HLTF genes occurred in 36%, 51% and 34% of the patients. The elevated mRNA levels of SUV39H1 were not associated with the hypermethylation of the 3 genes. However, the mRNA levels of DNMT1 were significantly different between patients with elevated mRNA levels of SUV39H1 and those without (1.62 +/- 0.84, 0.91 +/- 0.81, respectively; p = 0.007). Patients with elevated mRNA levels of SUV39H1 showed a higher prevalence of DNMT1 elevation than those without (61 vs. 35%, p = 0.0008). Patients with an elevated mRNA level of SUV39H1 had a 2.71 (95% CI = 1.09-4.48, p = 0.002) times greater risk of an elevated mRNA level of DNMT1, after controlling for age and gender. In conclusion, the present study suggests that SUV39H1 is significantly associated with DNMT1, but not with euchromatic promoter methylation in colorectal cancer.