Loss of LDOC1 Expression by Promoter Methylation in Cervical Cancer Cells

Identifying a Risk Signature of Methylation-Driven Genes as a Predictor of Survival Outcome for Colon Cancer Patients

Aberrant expression of gene is driven by its promoter methylation and is the key molecular basis of carcinogenic processes. This study aimed at identifying a risk signature of methylation-driven (MD) genes and evaluating its prognostic value for colon cancer (CC) patients. The expression profiles of methylation and mRNA in CC samples were obtained from the TCGA database, and the MethylMix algorithm was used to identify MD genes. The relationships between their expression levels and overall survival (OS) of CC patients were analyzed, and a prognostic signature of MD genes was established. The risk score of gene signature was calculated, and the median was used to divide all patients into high (H) and low (L) risk groups. The prognostic value of gene signature was tested by the TCGA cohort and an independent validation cohort (GSE17538 dataset). In total, 69 MD genes were identified, and 7 were associated with OS of CC patients. Ultimately, 4 (TWIST1, LDOC1, EPHX3, and STC2) were screened out to establish a risk signature. The H-risk patients (>0.923) had a worse OS than L-risk patients (≤0.923) in both the TCGA (5-year cumulative survival: 52.9% vs 72.0%, P=0.005) and GSE17538 cohort (49.4% vs 69.3%, P=0.004). The AUC values of MD genes signature for the prediction of 3- and 5-year OS were 0.648 and 0.643 in the TCGA dataset and 0.634 and 0.624 in the GSE17538 dataset, respectively. The risk signature of four MD genes was identified as an independent predictor of OS for CC patients (HR for TCGA dataset: 2.071, 95% CI=1.196-3.586, P=0.009; HR for GSE17538 dataset: 2.021, 95% CI=1.290-3.166, P=0.002). The risk signature of four MD genes might be a useful prognostic tool and help doctors improve the clinical management of CC patients.

Leucine zipper downregulated in cancer 1 may serve as a favorable prognostic biomarker by influencing proliferation, colony formation, cell cycle, apoptosis, and migration ability in hepatocellular carcinoma

Aims: Leucine zipper downregulated in cancer 1 (LDOC1) inhibits tumor growth in several cancers. However, the expression and function of LDOC1 in hepatocellular carcinoma (HCC) remain unknown. In this study, we aimed to investigate how LDOC1 influenced tumor progression and the biological functions of HCC.

Methods: The transcription levels of LDOC1 were determined using the GEPIA and UALCAN online databases and a real-time polymerase chain reaction. Western blot and immunohistochemistry were used to validate the protein levels of LDOC1. The online Kaplan-Meier Plotter was applied for survival analysis. Then lentivirus transfection was used to construct LDOC1 exogenous overexpression cell lines. Proliferation, clone formation, cell cycle, apoptosis, and migration assays were performed with the LDOC1-upregulated Huh7 and Hep3B cell lines. The phosphorylated and total levels of AKT and mTOR were determined using a Western blot to explore the potential molecular mechanism of LDOC1.

Results: In the GEPIA and UALCAN analyses, LDOC1 was lowly expressed in tumors, had high expression in normal tissue samples (p < 0.05), and negatively correlated with tumor grade progression. The down-regulation of LDOC1 in HCC was validated with real-time polymerase chain reaction, Western blot, and immunohistochemistry (all p < 0.05). LDOC1 transcription levels were negatively associated with overall, progression-free, recurrence-free, and disease-specific survival (all p < 0.05). The functional experiments suggested that the overexpression of LDOC1 contributed to increased G1 and G2 stages in Huh7, while increased G2 stage in Hep3B, and decreased cell proliferation, clone formation, and migration, as well as increased the apoptosis rate compared with the control group (all p < 0.05). Furthermore, LDOC1 up-regulation reduced the p-AKT/AKT and p-mTOR/mTOR, which indicates an inactivation of the AKT/mTOR pathway.

Conclusion: The tumor-suppressor LDOC1 varied in HCC and non-HCC tissues, which can serve as a candidate prognostic biomarker. LDOC1 influenced survival by affecting proliferation, colony formation, cell cycle, apoptosis, and migration ability, which might be attributed to the AKT/mTOR inhibition in HCC.

Dysregulated expression and functions of microRNA-330 in cancers: A potential therapeutic target

As small non-coding RNAs, MicroRNAs (miRNAs) bind to the 3' untranslated region (3'-UTR) of mRNA targets to control gene transcription and translation. The gene of miR-330 has two miRNA products, including miR-330-3p and miR-330-5p, which exhibit anti-tumorigenesis and/or pro-tumorigenesis effects in many kinds of malignancies. In cancers, miR-330-3p and miR-330-5p aberrant expression can influence many malignancy-related processes such as cell proliferation, migration, invasion, apoptosis and epithelial-mesenchymal transition, as well as angiogenesis and responsiveness to treatment. In many cancer types (such as lung, prostate, gastric, breast, bladder, ovarian, colorectal, and pancreatic cancer, and osteosarcoma), miR-330-5p acts as an anti-tumor agent. These cancers have low levels of miR-330-5p that leads to the upregulation of the tumor promotor target genes leading to tumor progression. Here, overexpression of miR-330-5p using miRNA inducers can prevent tumor development. Dual roles of miR-330-5p have been also indicated in the thyroid, liver and cervical cancers. Moreover, miR-330-3p exhibits pro-tumorigenesis effects in lung cancer, pancreatic cancer, osteosarcoma, bladder cancer, and cervical cancer. Here, downregulation of miR-330-3p using miRNA inhibitors can prevent tumor development. Demonstrated in breast and liver cancers, miR-330-3p also has dual roles. Importantly, the activities of miR-330-3p and/or miR-330-5p are regulated by upstream regulators long non-coding RNAs (lncRNAs), including circular and linear lncRNAs. This review comprehensively explained miR-330-3p and miR-330-5p role in development of cancers, while highlighting their downstream target genes and upstream regulators as well as possible therapeutic strategies.

LDOC1 as Negative Prognostic Marker for Vulvar Cancer Patients

So far, studies about targeted therapies and predictive biomarkers for vulva carcinomas are rare. The leucine zipper downregulated in cancer 1 gene (LDOC1) has been identified in various carcinomas as a tumor-relevant protein influencing patients' survival and prognosis. Due to the lack of information about LDOC1 and its exact functionality, this study focuses on the expression of LDOC1 in vulvar carcinoma cells and its surrounding immune cells as well as its correlation to clinicopathological characteristics and prognosis. Additionally, a possible regulation of LDOC1 in vulvar cancer cell lines via the NF-κB signaling pathway was analyzed. Vulvar carcinoma sections of 157 patients were immunohistochemically stained and examined regarding LDOC1 expression by using the immunoreactive score (IRS). To characterize LDOC1-positively stained immune cell subpopulations, immunofluorescence double staining was performed. The effect of the NF-κB inhibitor C-DIM 12 (3,3'-[(4-chlorophenyl)methylene]bis[1 H-indole]) on vulvar cancer cell lines A431 and SW 954 was measured according to MTT and BrdU assays. Baseline expression levels of LDOC1 in the vulvar cancer cell lines A431 and SW 954 was analyzed by real-time PCR. LDOC1 was expressed by about 90% of the cancer cells in the cytoplasm and about half of the cells in the nucleus. Cytoplasmatic expression of LDOC1 was associated with decreased ten-year overall survival of the patient, whereas nuclear staining showed a negative association with disease-free survival. Infiltrating immune cells were mainly macrophages followed by regulatory T cells. Incubation with C-DIM 12 decreased the cell viability and proliferation of vulvar cancer cell line A431, but not of cell line SW 954. LDOC1 expression on mRNA level was twice as high in the cell line A431 compared to the cell line SW 954. Overexpression of LDOC1 was associated with unfavorable overall and disease-free survival. Tumor growth could be inhibited by C-DIM 12 in vitro if the expressed LDOC1 level was high enough.

Discriminating Origin Tissues of Tumor Cell Lines by Methylation Signatures and Dys-Methylated Rules

DNA methylation is an essential epigenetic modification for multiple biological processes. DNA methylation in mammals acts as an epigenetic mark of transcriptional repression. Aberrant levels of DNA methylation can be observed in various types of tumor cells. Thus, DNA methylation has attracted considerable attention among researchers to provide new and feasible tumor therapies. Conventional studies considered single-gene methylation or specific loci as biomarkers for tumorigenesis. However, genome-scale methylated modification has not been completely investigated. Thus, we proposed and compared two novel computational approaches based on multiple machine learning algorithms for the qualitative and quantitative analyses of methylation-associated genes and their dys-methylated patterns. This study contributes to the identification of novel effective genes and the establishment of optimal quantitative rules for aberrant methylation distinguishing tumor cells with different origin tissues.

LDOC1 is differentially expressed in thyroid cancer and display tumor-suppressive function in papillary thyroid carcinoma

The leucine zipper downregulated in cancer 1 (LDOC1) has been proposed as a regulator of transcription and cell signaling. We have previously demonstrated that LDOC1 is differentially expressed in papillary thyroid carcinoma (PTC), this study was designed to characterize LDOC1 expression in thyroid follicle originated cancer tissues and to specifically evaluate its function in thyroid carcinogenesis. LDOC1 expression was performed in human normal thyroid and thyroid cancer. LDOC1 function was characterized, in two PTC cell lines (TPC1 and BCPAP), through the analysis of in vitro cell proliferation, apoptosis, migration, and invasion along with in vivo tumor xenograft growth. Transduced BCPAP cells were stimulated with tumor necrosis factor α, and the levels of nuclear P65, Bax, Bcl-2, c-Myc, and XIAP were assessed. A luciferase reporter assay was used to measure nuclear factor-κB (NF-κB) activity, and the functional connection between LDOC1 effect and NF-κB activity was determined using a specific NF-κB inhibitor. Our results revealed that LDOC1 was translocated from the nucleus to the cytoplasm in human thyroid cancer, and was significantly downregulated in PTC compared with normal thyroid. LDOC1 overexpression in TPC1 resulted in a significant suppression of the malignant phenotype, whereas LDOC1 ablation in BCPAP promoted this phenotype. Additional studies demonstrated that LDOC1 ablation facilitated nuclear P65 expression and NF-κB activity. NF-κB inhibition reversed the effects of LDOC1 ablation on proliferation, apoptosis, migration, and invasion. Our findings confirmed that LDOC1 is a novel therapeutic target in PTC and provides new insight into the role of LDOC1 in PTC progression, through NF-κΒ signaling suppression.

HAND2-AS1 inhibits invasion and metastasis of cervical cancer cells via microRNA-330-5p-mediated LDOC1

Background

Cervical cancer is a serious disease with complicated pathogenesis and thus there is an urgent need to find novel targets for the treatment. Recently, long non-coding RNAs (lncRNAs) have emerged as critical factors in tumorigenesis. In this study, we aimed to investigate the mechanism of HAND2 antisense RNA 1 (HAND2-AS1) on the invasion and metastasis of cervical cancer cells.

Methods

The expression patterns of HAND2-AS1, microRNA-330-5p (miR-330-5p) and leucine zipper down-regulated in cancer 1 (LDOC1) in cervical cancer were characterized by RT-qPCR and western blot analysis. Dual luciferase reporter assay and RIP were applied to verify relationship between HAND2-AS1, miR-330-5p and LDOC1. Fluorescence in situ hybridization (FISH) was used to detect the subcellular localization of HAND2-AS1. Besides, viability, invasion and migration ability of HeLa cells were investigated by cell counting kit-8 (CCK-8) and Transwell assays respectively. Hematoxylin-eosin staining was performed for lymph node metastasis detection. In addition, the tumor growth in nude mice was evaluated.

Results

Low expression of HAND2-AS1 and LDOC1, and high expression of miR-330-5p were detected in cervical cancer tissues and cells. It was found that binding of HAND2-AS1 to miR-330-5p results in upregulation of LDOC1 expression. Also, overexpressed HAND2-AS1 and LDOC1 or down-regulated miR-330-5p inhibited expression of proliferation-associated proteins Ki-67, PCNA, migration-associated proteins N-cad and invasion-related proteins MMP-2, MMP-9 as well as lymph node metastasis. Moreover, HAND2-AS1 inhibited tumor formation and lymph node metastasis by binding to miR-330-5p in vivo.

Conclusion

HAND2-AS1 promotes LDOC1 expression by competitively binding to miR-330-5p and consequently inhibiting cervical cancer cell invasion and metastasis. This could facilitate development of therapeutic strategies against cervical cancer.

Effects of LDOC1 on colorectal cancer cells via downregulation of the Wnt/β-catenin signaling pathway

Colorectal cancer (CRC) is one of the most common tumor types of the digestive tract. Its incidence and mortality rates are among the highest of all gastrointestinal tumor types. The expression of leucine zipper downregulated in cancer 1 (LDOC1) is decreased in numerous cancer types. In the present study, the aim was to investigate the role of LDOC1 and determine the potential molecular mechanisms of its action in CRC. The expression of LDOC1 in CRC tissues and adjacent normal tissues was detected by reverse transcription-quantitative polymerase chain reaction and immunohistochemistry. LDOC1 expression in four CRC cell lines, compared with normal colorectal tissue, was determined by reverse transcription- polymerase chain reaction (RT-PCR), and two cell lines with relatively low expression were screened. Human LDOC1 cDNA was inserted into a lentiviral vector, and transfected into HCT-116 and Caco2 cell lines. The transfection efficiency was identified by RT-PCR and western blot analysis. Cell proliferation was detected by Cell Counting Kit-8 and colony formation assays. Cell cycle and apoptosis were detected by flow cytometry assay. Migration and invasion were assessed using Transwell and Matrigel assays, respectively. Additionally, whether LDOC1 regulates the Wnt/β-catenin pathway was investigated by western blot analysis, and the expression and localization of β-catenin in CRC cells were demonstrated by cellular immunofluorescence. LDOC1 expression was downregulated in CRC tissues and cells. LDOC1 overexpression inhibited cell proliferation, migration and invasion, but promoted cells apoptosis. Furthermore, LDOC1 downregulated the Wnt/β-catenin pathway in CRC. In conclusion, LDOC1 is a tumor suppressor in CRC and it inhibits cell proliferation and promotes cell apoptosis. Additionally, it inhibits CRC cell metastasis by downregulating the Wnt/β-catenin signaling pathway.

Salivary LDOC1 is a gender-difference biomarker of oral squamous cell carcinoma

Background

The X-linked tumor suppressor gene LDOC1 is reported to be involved in oral cancer. The detection of biomarkers in salivary RNA is a non-invasive strategy for diagnosing many diseases. The aim of the present study was to investigate the potential of salivary LDOC1 as a biomarker of oral cancer.

Methods

We determined the expression levels of LDOC1 in the saliva of oral squamous cell carcinoma (OSCC) subjects, and investigated its correlation with various clinicopathological characteristics. The expression levels of salivary LDOC1 were detected in 53 OSCC subjects and 43 healthy controls using quantitative reverse transcription polymerase chain reaction (qRT-PCR) analysis. We used Fisher’s exact test to analyze the correlations between expression levels and clinicopathological characteristics.

Results

Salivary LDOC1 was significantly upregulated in females with OSCC (p = 0.0072), and significantly downregulated in males with OSCC (p = 0.0206). Eighty-nine percent of male OSCC subjects who smoked expressed low levels of LDOC1. OSCC cell lines derived from male OSCC subjects expressed low levels of LDOC1.

Conclusions

A high level of salivary LDOC1 expression is a biomarker of OSCC in females. A high percentage of male OSCC subjects who smoke express low levels of salivary LDOC1. A low level of salivary LDOC1 expression is a biomarker of OSCC in males.

Novel STAT3 Inhibitor LDOC1 Targets Phospho-JAK2 for Degradation by Interacting with LNX1 and Regulates the Aggressiveness of Lung Cancer

Meta-analysis revealed that Leucine Zipper Down-Regulated In Cancer 1 (LDOC1) increased methylation more in people with lung tumors than in those who were healthy and never smoked. Quantitative methylation-specific PCR revealed that cigarette smoke condensate (CSC) exposure drives LDOC1 promoter hypermethylation and silence in human bronchial cells. Immunohistochemistry studies showed that LDOC1 downregulation is associated with poor survival of patients with lung cancer. Loss and gain of LDOC1 functions enhanced and attenuated aggressive phenotypes in lung adenocarcinoma A549 and non⁻small cell lung carcinoma H1299 cell lines, respectively. We found that LDOC1 deficiency led to reinforcing a reciprocal loop of IL-6/JAK2/STAT3, through which LDOC1 mediates the cancer progression. LDOC1 knockdown considerably augmented tumorigenesis and the phosphorylation of JAK2 and STAT3 in vivo. Results from immunoprecipitation and immunofluorescent confocal microscopy indicated that LDOC1 negatively regulates JAK2 activity by forming multiple protein complexes with pJAK2 and E3 ubiquitin-protein ligase LNX1, and in turn, LDOC1 targets pJAK2 to cause ubiquitin-dependent proteasomal degradation. LDOC1 deficiency attenuates the interactions between LNX1 and pJAK2, leading to ineffective ubiquitination of pJAK2, which activates STAT3. Overall, our results elucidated a crucial role of LDOC1 in lung cancer and revealed how LDOC1 acts as a bridge between tobacco exposure and the IL-6/JAK2/STAT3 loop in this human malignancy.

NF-κB upregulation through epigenetic silencing of LDOC1 drives tumor biology and specific immunophenotype in Group A ependymoma

Background

Inflammation has been identified as a hallmark of high-risk Group A (GpA) ependymoma (EPN). Chronic interleukin (IL)-6 secretion from GpA tumors drives an immune suppressive phenotype by polarizing infiltrating monocytes. This study determines the mechanism by which IL-6 is dysregulated in GpA EPN.

Methods

Twenty pediatric GpA and 21 pediatric Group B (GpB) EPN had gene set enrichment analysis for MSigDB Hallmark gene sets performed. Protein and RNA from patients and cell lines were used to validate transcriptomic findings. GpA cell lines 811 and 928 were used for in vitro experiments performed in this study.

Results

The nuclear factor-kappaB (NF-κB) pathway is a master regulator of IL-6 and a signaling pathway enriched in GpA compared with GpB EPN. Knockdown of NF-κB led to significant downregulation of IL-6 in 811 and 928. NF-κB activation was independent of tumor necrosis factor alpha (TNF-α) stimulation in both cell lines, suggesting that NF-κB hyperactivation is mediated through an alternative mechanism. Leucine zipper downregulated in cancer 1 (LDOC1) is a known transcriptional repressor of NF-κB. In many cancers, LDOC1 promoter is methylated, which inhibits gene transcription. We found decreased LDOC1 gene expression in GpA compared with GpB EPN, and in other pediatric brain tumors. EPN cells treated with 5AZA-DC, demethylated LDOC1 regulatory regions, upregulated LDOC1 expression, and concomitantly decreased IL-6 secretion. Stable knockdown of LDOC1 in EPN cell lines resulted in a significant increase in gene transcription of v-rel avian reticuloendotheliosis viral oncogene homolog A, which correlated to an increase in NF-κB target genes.

Conclusion

These results suggest that epigenetic silencing of LDOC1 in GpA EPN regulates tumor biology and drives inflammatory immune phenotype.

The Progress of Methylation Regulation in Gene Expression of Cervical Cancer

Cervical cancer is one of the most common gynecological tumors in females, which is closely related to high-rate HPV infection. Methylation alteration is a type of epigenetic decoration that regulates the expression of genes without changing the DNA sequence, and it is essential for the progression of cervical cancer in pathogenesis while reflecting the prognosis and therapeutic sensitivity in clinical practice. Hydroxymethylation has been discovered in recent years, thus making 5-hmC, the more stable marker, attract more attention in the field of methylation research. As markers of methylation, 5-hmC and 5-mC together with 5-foC and 5-caC draw the outline of the reversible cycle, and 6-mA takes part in the methylation of RNA, especially mRNA. Furthermore, methylation modification participates in ncRNA regulation and histone decoration. In this review, we focus on recent advances in the understanding of methylation regulation in the process of cervical cancer, as well as HPV and CIN, to identify the significant impact on the prospect of overcoming cervical cancer.

LDOC1 regulates Wnt5a expression and osteosarcoma cell metastasis and is correlated with the survival of osteosarcoma patients

Osteosarcomas are common bone malignancies in children and adolescents. LDOC1 (leucine zipper, down-regulated in cancer 1), a tumor suppressor, is down-regulated in many cancers. In this study, we investigated the role of LDOC1 in tumor metastasis and its prognostic significance in osteosarcomas. We established osteosarcoma cells stably expressing LDOC1, driven by an HIV-based lentiviral system. We investigated the impact of LDOC1 on migration and invasion abilities in these cells using a transwell assay. LDOC1-associated changes in expression of metastasis-promoting genes were analyzed with a quantitative real-time polymerase chain reaction primer array. A xenograft tumor model (n = 7 mice/group) was used to assess the effect of LDOC1 on osteosarcoma metastasis in vivo. The overall survival and disease-free survival of osteosarcoma patients (n = 74) were analyzed retrospectively based on immunohistochemical analysis of LDOC1 levels in tumors and Kaplan-Meier analysis. LDOC1-expressing osteosarcoma cells displayed decreased migration and invasion in vitro. The quantitative real-time polymerase chain reaction primer array data showed that increased LDOC1 expression up-regulated many metastasis-suppressor genes. In the xenograft model, micro-computed tomography imaging data indicated that increased LDOC1 expression is associated with weaker lung metastasis ability. The Wnt5a signaling pathway promotes osteosarcoma metastasis; LDOC1 expression decreased Wnt5a levels in osteosarcoma cells. Kaplan-Meier analysis showed that higher LDOC1 expression was associated with improved osteosarcoma patient overall survival and disease free survival (p = 0.022). Our data show that LDOC1 is a tumor suppressor in osteosarcoma, and that it regulates metastasis of osteosarcoma cells. Furthermore, LDOC1 might be a valuable prognostic marker in osteosarcomas.

Leucine Zipper Down-regulated in Cancer-1 (LDOC1) interacts with Guanine nucleotide binding protein-like 3-like (GNL3L) to modulate Nuclear Factor-kappa B (NF-κB) signaling during cell proliferation

Guanine nucleotide binding protein-like 3-like (GNL3L) is an evolutionarily conserved putative nucleolar GTPase belonging to the HSR1-MMR1 family. In the present study, using protein-protein interaction assays, we show that Leucine Zipper Down-regulated in Cancer-1 (LDOC1) is a novel interacting partner of GNL3L. Furthermore, our results reveal that ectopic expression of LDOC1 destabilizes endogenous GNL3L levels and down modulates GNL3L-induced cell proliferation, in contrast, the knockdown of LDOC1 potentiates cell proliferation upon GNL3L expression. Interestingly, GNL3L upregulates NF-κB dependent transcriptional activity by modulating the expression of NF-κB subunit p65, which is reversed upon co-expression of LDOC1 with GNL3L. GNL3L also potentiates TNF-α mediated NF-κB activity. In addition, anti-apoptotic function of GNL3L is impaired upon p65 knockdown, suggesting its critical role in GNL3L mediated cell proliferation/survival. An inverse correlation of GNL3L and LDOC1 expression profiles in various tumor tissues from BioXpress database indicate their critical role in cancer. Collectively, our data provides evidence that GNL3L-LDOC1 interplay regulates cell proliferation through the modulation of NF-κB pathway during tumorigenesis.

LDOC1 silenced by cigarette exposure and involved in oral neoplastic transformation

Previously, we identified global epigenetic aberrations in smoking-associated oral squamous cell carcinoma (OSCC). We hypothesized that cigarette exposure triggers OSCC through alteration of the methylome of oral cells. Here we report that cigarette smoke condensate (CSC) significantly changes the genomic 5-methyldeoxycytidine content and nuclear accumulation of DNA methyltransferase 1 (DNMT1) and DNMT3A in human untransformed oral cells. By using integrated analysis of cDNA and methylation arrays of the smoking-associated dysplastic oral cell line and OSCC tumors, respectively, we identified four epigenetic targets—UCHL1, GPX3, LXN, and LDOC1—which may be silenced by cigarette. Results of quantitative methylation-specific PCR showed that among these four genes, LDOC1 promoter was the most sensitive to CSC. LDOC1 promoter hypermethylation and gene silencing followed 3 weeks of CSC treatment. LDOC1 knockdown led to a proliferative response and acquired clonogenicity of untransformed oral cells. Immunohistochemistry showed that LDOC1 was downregulated in 53.3% (8/15) and 57.1% (20/35) of premalignant oral tissues and early stage OSCCs, respectively, whereas 76.5% (13/17) of normal oral tissues showed high LDOC1 expression. Furthermore, the microarray data showed that LDOC1 expression had decreased in the lung tissues of current smokers compared with that in those of never smokers and had significantly decreased in the lung tumors of smokers compared with that in normal lung tissues. Our data suggest that CSC-induced promoter methylation may contribute to LDOC1 downregulation, thereby conferring oncogenic features to oral cells. These findings also imply a tumor suppressor role of LDOC1 in smoking-related malignancies such as OSCC and lung cancer.

Not so bad after all: retroviruses and long terminal repeat retrotransposons as a source of new genes in vertebrates

Viruses and transposable elements, once considered as purely junk and selfish sequences, have repeatedly been used as a source of novel protein-coding genes during the evolution of most eukaryotic lineages, a phenomenon called 'molecular domestication'. This is exemplified perfectly in mammals and other vertebrates, where many genes derived from long terminal repeat (LTR) retroelements (retroviruses and LTR retrotransposons) have been identified through comparative genomics and functional analyses. In particular, genes derived from gag structural protein and envelope (env) genes, as well as from the integrase-coding and protease-coding sequences, have been identified in humans and other vertebrates. Retroelement-derived genes are involved in many important biological processes including placenta formation, cognitive functions in the brain and immunity against retroelements, as well as in cell proliferation, apoptosis and cancer. These observations support an important role of retroelement-derived genes in the evolution and diversification of the vertebrate lineage.

Epigenetic silencing of the LDOC1 tumor suppressor gene in ovarian cancer cells

PURPOSE

Due to very unspecific symptoms ovarian cancer often is diagnosed only at a late stage of the disease. Thus, morbidity and mortality of the patients are high. Even the established tumor marker CA12-5 shows only low specificity, rising the need for alternative biomarkers capable of detecting early stages of ovarian cancer. We analyzed the expression of the tumor suppressor candidate gene LDOC1 (leucine zipper downregulated in cancer 1) as a potential early biomarker in ovarian cancer cell lines.

METHODS

A total of seven ovarian cancer cell lines were analyzed by RT-PCR (reverse transcriptase polymerase chain reaction) and real-time PCR for expression of LDOC1. Verification of promoter methylation was performed using methylation-specific primers on bisulfite-modified genomic DNA.

RESULTS

Three out of seven ovarian cancer cell lines showed a complete loss of LDOC1 gene expression. LDOC1 silencing was caused neither by gene deletion nor gene rearrangements, but by methylation and subsequent inactivation of the concerned promoter as proofed by methylation specific primers. Similarly, promoter methylation could be inhibited by adding AdC (5-aza-2'-deoxycytidine), an inhibitor of DNA methyltransferases. As a result, a reactivation of the LDOC1 gene was seen.

CONCLUSIONS

The tumor suppressor gene LDOC1 in ovarian cancer cell lines is downregulated by promoter methylation and thus may serve as an early biomarker. Further investigation will show if detection of methylated LDOC1 in peripheral blood has both adequate sensitivity and specificity for a timely non-invasive detection of ovarian cancer.