Evidence that RASSF1C stimulation of lung cancer cell proliferation depends on IGFBP-5 and PIWIL1 expression levels

The Role of RASSF1C in the Tumor Microenvironment

The tumor microenvironment (TME) plays a vital role in tumor invasion and metastasis and provides a rich environment for identifying novel therapeutic targets. The TME landscape consists of an extracellular matrix (ECM) and stromal cells. ECM is a major component of TME that mediates the interaction between cancer cells and stromal cells to promote invasion and metastasis. We have shown in published work that RASSF1C promotes cancer stem cell development, migration, and drug resistance, in part, by promoting EMT through a mechanism that involves up-regulation of the PIWIL1-piRNA axis. Consistent with this, in this study, we demonstrate that RASSF1C promotes lung cancer metastasis in vivo using an orthotopic mouse model. Interestingly, two target genes identified in a previously conducted microarray study to be up-regulated by RASSF1C in breast and non-small cell lung cancer (NSCLC) cells are prolyl 4-hydroxylase alpha-2 (P4HA2) and procollagen-lysine, 2-oxoglutarate 5-dioxygenase 2 (PLOD2). In cancer, P4H2A and PLOD2 are vital for collagen posttranslational modification and folding leading to the formation of a stiff ECM and induction of EMT and cancer stem cell marker gene expression, resulting in metastatic dissemination. Here, we also show that overexpression of RASSF1C up-regulates Collagen I, P4HA2, and PLOD2 in vitro. Up-regulation of P4HA2 and PLOD2 by RASSF1C was also confirmed in lung and breast cancer cells in vivo using mouse models. Further, we found that treatment of wildtype lung cancer cells or lung cancer cells overexpressing RASSF1C or PIWIL1 with piR-35127 and 46545 (both down-regulated by RASSF1C) decreased lung cancer cell invasion/migration. Taken together, our findings suggest that RASSF1C may promote lung cancer cell ECM remodeling to induce lung cancer cell stemness, invasion, and metastasis, in part, by up-regulating a previously unknown PIWIL1-P4HA2-PLOD2 pathway. Furthermore, piR-35127 and piR-46545 could potentially be important anti-metastatic tools.

Multifunctional Roles of Betulinic Acid in Cancer Chemoprevention: Spotlight on JAK/STAT, VEGF, EGF/EGFR, TRAIL/TRAIL-R, AKT/mTOR and Non-Coding RNAs in the Inhibition of Carcinogenesis and Metastasis

The pursual of novel anticancer molecules from natural sources has gained worthwhile appreciation, and a significant fraction of conceptual knowledge has revolutionized our understanding about heterogeneous nature of cancer. Betulinic acid has fascinated interdisciplinary researchers due to its tremendous pharmacological properties. Ground-breaking discoveries have unraveled previously unprecedented empirical proof-of-concept about momentous chemopreventive role of betulinic acid against carcinogenesis and metastasis. Deregulation of cell signaling pathways has been reported to play a linchpin role in cancer progression and colonization of metastatically competent cancer cells to the distant organs for the development of secondary tumors. Importantly, betulinic acid has demonstrated unique properties to mechanistically modulate oncogenic transduction cascades. In this mini-review, we have attempted to provide a sophisticated compendium of regulatory role of betulinic acid in cancer chemoprevention. We have partitioned this multi-component review into different sections in which we summarized landmark research-works which highlighted betulinic acid mediated regulation of JAK/STAT, VEGF, EGF/EGFR, TRAIL/TRAIL-R, AKT/mTOR and ubiquitination pathways in the inhibition of cancer. In parallel, betulinic acid mediated regulation of signaling cascades and non-coding RNAs will be critically analyzed in cell culture and animal model studies. Better comprehension of the pharmaceutical features of betulinic acid and mapping of the existing knowledge gaps will be valuable in the translatability of preclinical studies into rationally designed clinical trials.

PIWI-interacting RNA (piRNA): a narrative review of its biogenesis, function, and emerging role in lung cancer

Cancer remains elusive in many aspects, especially in its causes and control. After protein profiling, genetic screening, and mutation studies, scientists now have turned their attention to epigenetic modulation. This new arena has brought to light the world of noncoding RNA (ncRNA). Although very complicated and often confusing, ncRNA domains are now among the most attractive molecular markers for epigenetic control of cancer. Long ncRNA and microRNA (miRNA) have been studied best among the noncoding genome and huge data have accumulated regarding their inhibitory and promoting effects in cancer. Another sector of ncRNAs is the world of PIWI-interacting RNAs (piRNAs). Initially discovered with the asymmetric division of germline stem cells in the Drosophila ovary, piRNAs have a unique capability to associate with mammalian proteins analogous to P-element induced wimpy testis (PIWI) in Drosophila and are capable of silencing transposons. After a brief introduction to its discovery timelines, the present narrative review covers the biogenesis, function, and role of piRNAs in lung cancer. The effects on lung cancer are highlighted under sections of cell proliferation, stemness maintenance, metastasis, and overall survival, and the review concludes with a discussion of recent discoveries of another class of small ncRNAs, the piRNA-like RNAs (piR-Ls).

Biological effects and regulation of IGFBP5 in breast cancer

The insulin-like growth factor receptor (IGF1R) pathway plays an important role in cancer progression. In breast cancer, the IGF1R pathway is linked to estrogen-dependent signaling. Regulation of IGF1R activity is complex and involves the actions of its ligands IGF1 and IGF2 and those of IGF-binding proteins (IGFBPs). Six IGFBPs are known that share the ability to form complexes with the IGFs, by which they control the bioavailability of these ligands. Besides, each of the IGFBPs have specific features. In this review, the focus lies on the biological effects and regulation of IGFBP5 in breast cancer. In breast cancer, estrogen is a critical regulator of IGFBP5 transcription. It exerts its effect through an intergenic enhancer loop that is part of the chromosomal breast cancer susceptibility region 2q35. The biological effects of IGFBP5 depend upon the cellular context. By inhibiting or promoting IGF1R signaling, IGFBP5 can either act as a tumor suppressor or promoter. Additionally, IGFBP5 possesses IGF-independent activities, which contribute to the complexity by which IGFBP5 interferes with cancer cell behavior.

Piwi-Interacting RNAs: A New Class of Regulator in Human Breast Cancer

P-element-induced wimpy testis (Piwi)-interacting RNAs (piRNAs) are a class of germline-enriched small non-coding RNA that associate with Piwi family proteins and mostly induce transposon silencing and epigenetic regulation. Emerging evidence indicated the aberrant expression of Piwil proteins and associated piRNAs in multiple types of human cancer including breast cancer. Although the majority of piRNAs in breast cancer remains unclear of the function mainly due to the variety of regulatory mechanisms, the potential of piRNAs serving as biomarkers for cancer diagnosis and prognosis or therapeutic targets for cancer treatment has been demonstrated by in vitro and in vivo studies. Herein we summarized the research progress of oncogenic or tumor suppressing piRNAs and their regulatory mechanisms in regulating human breast cancer, including piR-021285, piR-823, piR-932, piR-36712, piR-016658, piR-016975 and piR-4987. The challenges and perspectives of piRNAs in the field of human cancer were discussed.

PiWi RNA in Neurodevelopment and Neurodegenerative disorders

Shedding light on the mysterious dark matter of the genome gears up the knowledge of modern biology. Beyond the genome, epigenome layers an untraveled path of fundamental biological and functional roles of gene regulation. Extraordinary character- P element wimpy testis-induced (PiWi)-interacting RNA (piRNA) is a type of small non-coding RNA that serves as a defender that imposes genomic and cellular defense by silencing nucleic and structural invaders. PIWI proteins and piRNAs appear in both reproductive and somatic cells, though germ line richness is partially unraveled more as it was originally discovered. The foremost function is to suppress invasive DNA sequences, which move within genomic DNA referred to as transposon elements (TEs) and downstream target genes via Transcriptional gene silencing (TGS) and Post-translational gene silencing (PTGS). Germline piRNAs maintain genomic integrity, stability, sternness, and impact imprinting expression. Somatic tissue-specific piRNAs have been surprised by their novel roles. piRNA regulates neurodevelopmental processes in metazoans, including humans. Neural heterogeneity, neurogenesis, neural plasticity, and transgenerational inheritance of adaptive and long-term memory are governed by the PIWI pathway. Neuro-developmental, neurodegenerative or psychiatric illness are the outcome of dysregulated piRNA. Aberrant piRNA signature causes inappropriate switching on or off genes by activation of TEs, incorrect epigenetic tags on DNA, and or histones. Defective piRNA regulation leads to abnormal brain development and neurodegenerative etiology, promoting life-threatening disorders. Exemplification of exciting roles of piRNA is in infancy, so future investigation may expand on these observations using innovative techniques and launch them as impending biomarkers for diagnostics and therapeutics. In this current review, we have summarized the possible gene molecular role of piRNAs regulating neurobiology and contributing as uncharted biomarkers and therapeutic targets for life-threatening diseases.

SMAD1 as a biomarker and potential therapeutic target in drug-resistant multiple myeloma

BACKGROUND

SMAD1, a central mediator in TGF-β signaling, is involved in a broad range of biological activities including cell growth, apoptosis, development and immune response, and is implicated in diverse type of malignancies. Whether SMAD1 plays an important role in multiple myeloma (MM) pathogenesis and can serve as a therapeutic target are largely unknown.

METHODS

Myeloma cell lines and primary MM samples were used. Cell culture, cytotoxicity and apoptosis assay, siRNA transfection, Western blot, RT-PCR, Soft-agar colony formation, and migration assay, Chromatin immunoprecipitation (Chip), animal xenograft model studies and statistical analysis were applied in this study.

RESULTS

We demonstrate that SMAD1 is highly expressed in myeloma cells of MM patients with advanced stages or relapsed disease, and is associated with significantly shorter progression-free and overall survivals. Mechanistically, we show that SMAD1 is required for TGFβ-mediated proliferation in MM via an ID1/p21/p27 pathway. TGF-β also enhanced TNFα-Induced protein 8 (TNFAIP8) expression and inhibited apoptosis through SMAD1-mediated induction of NF-κB1. Accordingly, depletion of SMAD1 led to downregulation of NF-κB1 and TNFAIP8, resulting in caspase-8-induced apoptosis. In turn, inhibition of NF-κB1 suppressed SMAD1 and ID1 expression uncovering an autoregulatory loop. Dorsomorphin (DM), a SMAD1 inhibitor, exerted a dose-dependent cytotoxic effect on drug-resistant MM cells with minimal cytotoxicity to normal hematopoietic cells, and further synergized with the proteasomal-inhibitor bortezomib to effectively kill drug-resistant MM cells in vitro and in a myeloma xenograft model.

CONCLUSIONS

This study identifies SMAD1 regulation of NF-κB1/TNFAIP8 and ID1-p21/p27 as critical axes of MM drug resistance and provides a potentially new therapeutic strategy to treat drug resistance MM through targeted inhibition of SMAD1.

Critical Roles of PIWIL1 in Human Tumors: Expression, Functions, Mechanisms, and Potential Clinical Implications

P-element-induced wimpy testis (PIWI)-interacting RNAs (piRNAs) are a class of small non-coding RNA molecules that are 24-31 nucleotides in length. PiRNAs are thought to bind to PIWI proteins (PIWL1-4, a subfamily of Argonaute proteins), forming piRNA/PIWI complexes that influence gene expression at the transcriptional or post-transcriptional levels. However, it has been recently reported that the interaction of PIWI proteins with piRNAs does not encompass the entire function of PIWI proteins in human tumor cells. PIWIL1 (also called HIWI) is specifically expressed in the testis but not in other normal tissues. In tumor tissues, PIWIL1 is frequently overexpressed in tumor tissues compared with normal tissues. Its high expression is closely correlated with adverse clinicopathological features and shorter patient survival. Upregulation of PIWIL1 drastically induces tumor cell proliferation, epithelial-mesenchymal transition (EMT), invasion, cancer stem-like properties, tumorigenesis, metastasis and chemoresistance, probably via piRNA-independent mechanisms. In this article, we summarize the current existing literature on PIWIL1 in human tumors, including its expression, biological functions and regulatory mechanisms, providing new insights into how the dysregulation of PIWIL1 contributes to tumor initiation, development and chemoresistance through diverse signaling pathways. We also discuss the most recent findings on the potential clinical applications of PIWIL1 in cancer diagnosis and treatment.

piRNAs: biogenesis and their potential roles in cancer

With the length of about 26-31 nt, PIWI-interacting RNA (piRNA) is a small non-coding RNA (ncRNA) that interacts with PIWI proteins to form the piRNA silencing complex (piRISC). PIWI is a subfamily of Argonaute, and piRNA must bind to PIWI to exert its regulatory role. Current studies indicated that piRNA and PIWI are significantly abnormally expressed in gastric, breast, kidney, colon, and lung cancers, and are involved in the initiation, progression, and metastasis of cancers, which may be the potential diagnostic tools, prognostic markers, and therapeutic targets for cancers. By reviewing piRNA recent studies, this research summarized the mechanism of piRNA generation and the functions of piRNA/PIWI in gastric, breast, kidney, colon, and lung cancers, providing a reference value for further piRNA research.

The impact of the RASSF1C and PIWIL1 on DNA methylation: the identification of GMIP as a tumor suppressor

INTRODUCTION

Recently we have identified a novel RASSF1C-PIWIL1-piRNA pathway that promotes lung cancer cell progression and migration. PIWI-like proteins interact with piRNAs to form complexes that regulate gene expression at the transcriptional and translational levels. We have illustrated in previous work that RASSF1C modulates the expression of the PIWIL1-piRNA gene axis, suggesting the hypothesis that the RASSF1C-PIWI-piRNA pathway could potentially contribute to lung cancer stem cell development and progression, in part, through modulation of gene methylation of both oncogenic and tumor suppressor genes. Therefore, we tested this hypothesis using a non-small cell lung cancer (NSCLC) cell model to identify Candidate Differentially Methylated Regions (DMRs) modulated by the RASSF1C-PIWIL1-piRNA pathway.

MATERIALS AND METHODS

We studied the impact of over-expressing RASSF1C and knocking down RASSF1C and PIWIL1 expression on global gene DNA methylation in the NSCLC cell line H1299 using the Reduced Representation Bisulfite Sequencing (RRBS) method.

RESULTS

DMRs were identified by comparing DNA methylation profiles of experimental and control cells. Over-expression of RASSF1C and knocking down RASSF1C and PIWIL1 modulated DNA methylation of genomic regions; and statistically significant candidate genes residing DMR regions in lung cancer cells were identified, including oncogenes and tumor suppressors. One of the hypermethylated genes, Gem Interacting Protein (GMIP), displays tumor suppressor properties. GMIP expression attenuates lung cancer cell migration, and its over-expression is associated with longer survival of lung cancer patients.

CONCLUSIONS

The RASSF1C-PIWI-piRNA pathway modulates key oncogenes and tumor suppressor genes. GMIP is hypermethylated by this pathway and has tumor suppressor properties.

Integrative Analysis of Pathological Images and Multi-Dimensional Genomic Data for Early-Stage Cancer Prognosis

The integrative analysis of histopathological images and genomic data has received increasing attention for studying the complex mechanisms of driving cancers. However, most image-genomic studies have been restricted to combining histopathological images with the single modality of genomic data (e.g., mRNA transcription or genetic mutation), and thus neglect the fact that the molecular architecture of cancer is manifested at multiple levels, including genetic, epigenetic, transcriptional, and post-transcriptional events. To address this issue, we propose a novel ordinal multi-modal feature selection (OMMFS) framework that can simultaneously identify important features from both pathological images and multi-modal genomic data (i.e., mRNA transcription, copy number variation, and DNA methylation data) for the prognosis of cancer patients. Our model is based on a generalized sparse canonical correlation analysis framework, by which we also take advantage of the ordinal survival information among different patients for survival outcome prediction. We evaluate our method on three early-stage cancer datasets derived from The Cancer Genome Atlas (TCGA) project, and the experimental results demonstrated that both the selected image and multi-modal genomic markers are strongly correlated with survival enabling effective stratification of patients with distinct survival than the comparing methods, which is often difficult for early-stage cancer patients.

Methylation Dynamics of RASSF1A and Its Impact on Cancer

5-methyl cytosine (5mC) is a key epigenetic mark entwined with gene expression and the specification of cellular phenotypes. Its distribution around gene promoters sets a barrier for transcriptional enhancers or inhibitor proteins binding to their target sequences. As a result, an additional level of regulation is added to the signals that organize the access to the chromatin and its structural components. The tumor suppressor gene RASSF1A is a microtubule-associated and multitasking scaffold protein communicating with the RAS pathway, estrogen receptor signaling, and Hippo pathway. RASSF1A action stimulates mitotic arrest, DNA repair and apoptosis, and controls the cell cycle and cell migration. De novo methylation of the RASSF1A promoter has received much attention due to its increased frequency in most cancer types. RASSF1A methylation is preceded by histones modifications and could represent an early molecular event in cell transformation. Accordingly, RASSF1A methylation is proposed as an epigenetic candidate marker in many cancer types, even though an inverse correlation of methylation and expression remains to be fully ascertained. Some findings indicate that the epigenetic abrogation of RASSF1A can promote the alternative expression of the putative oncogenic isoform RASSF1C. Understanding the complexity and significance of RASSF1A methylation is instrumental for a more accurate determination of its biological and clinical role. The review covers the molecular events implicated in RASSF1A methylation and gene silencing and provides a deeper view into the significance of the RASSF1A methylation patterns in a number of gastrointestinal cancer types.

RASSF1C regulates miR-33a and EMT marker gene expression in lung cancer cells

RASSF1C functions as an oncogene in lung cancer cells by stimulating proliferation and migration, and reducing apoptosis. Further, RASSF1C up-regulates important protein-coding and non-coding genes involved in lung cancer cell growth, including the stem cell self-renewal gene, piwil1, and small noncoding PIWI-interacting RNAs (piRNAs). In this article, we report the identification of microRNAs (miRNAs) that are modulated in lung cancer cells over-expressing RASSF1C. A lung cancer-specific miRNA PCR array screen was performed to identify RASSF1C target miRNA-coding genes using RNA isolated from the lung cancer cell line H1299 stably over-expressing RASSF1C and corresponding control. Several modulated miRNA genes were identified that are important in cancer cell proliferation and survival. Among the miRNAs down-regulated by RASSF1C is miRNA-33a-5p (miRNA-33a), which functions as a tumor suppressor in lung cancer cells. We validated that over-expression of RASSF1C down-regulates miR-33a expression and RASSF1C knockdown up-regulates miR-33a expression. We found that RASSF1C over-expression also increases β-catenin, vimentin, and snail protein levels in cells over-expressing miR-33a. In addition, we found that RASSF1C up-regulates the expression of ABCA1 mRNA which is a known target of miR-33a. Our findings suggest that RASSF1C may promote lung epithelial mesenchymal transition (EMT), resulting in the development of a lung cancer stem cell phenotype, progression, and metastasis, in part, through modulation of miR-33a expression. Our findings reveal a new mechanistic insight into how RASSF1C functions as an oncogene.

PIWI-like protein 1 upregulation promotes gastric cancer invasion and metastasis

Background

PIWI-like protein 1 (PIWIL1) is an important member of the Argonaute protein family and is closely related to the malignant behaviors of tumor cells. This study aimed to investigate the relationship between PIWIL1 and gastric cancer (GC).

Methods

We investigated PIWIL1 expression status in GC tissues as well as its association with clinicopathological characteristics and prognosis of GC patients. PIWIL1 siRNA was transfected into a GC cell line to elucidate its impact on malignant biological behavior.

Results

The results showed that PIWIL1 was upregulated in GC tissues and correlated with tumor differentiation, lymph node status, and TNM stage. The high PIWIL1 expression was an independent predictor for the prognosis of patients with GC. Silencing of PIWIL1 expression in GC cell lines suppressed tumor cell proliferation, migration, and invasion.

Conclusion

High PIWIL1 expression suggests a poor prognosis for GC patients and PIWIL1 can serve as an important molecular marker for predicting the prognosis of GC patients.

Identification and characterization of RASSF1C piRNA target genes in lung cancer cells

RASSF1C up-regulates important genes involved in lung cancer cell growth, including a stem cell self-renewal gene, piwil1. In this article, we report the identification of small noncoding PIWI-interacting RNAs (piRNAs) in lung cancer cells over-expressing RASSF1C. A piRNA microarray screen was performed using RNA isolated from the lung cancer cell line H1299 stably over-expressing RASSF1C and corresponding control. The piRNA microarray screen identified several piRNAs that are regulated by RASSF1C and we have validated the expression of two up-regulated piRNAs (piR-34871 and piR-52200) and two down-regulated piRNAs (piR-35127 and piR-46545) in lung cancer cells with silenced and over-expressed RASSF1C using RT-PCR. We also assessed the expression of these four piRNAs in lung tumor and matched normal tissues (n = 12). We found that piR-34871 and piR-52200 were up-regulated in 58% and 50%, respectively; while piR-35127 and piR-46545 were down-regulated in 50% in lung tumor tissues tested. The expression of piR-35127 was inversely correlated with RASSF1C expression in 10/12 tumor tissues. Over-expression of piR-35127 and piR-46545 and knock-down of piR-34871 and piR-52200 significantly reduced normal lung and breast epithelial cell proliferation and cell colony formation as well as proliferation of lung cancer cell lines (A549 and H1299) and breast cancer cell lines (Hs578T and MDA-MB-231). This suggests that these novel piRNAs may potentially be involved in regulating lung cell transformation and tumorigenesis. RASSF1C may potentially modulate the expression of its piRNA target genes through attenuation of the AMPK pathway, as over-expression of RASSF1C resulted in reduction of p-AMPK, p21, and p27 protein levels.

Expression Status of PIWIL1 as a Prognostic Marker of Colorectal Cancer

The PIWI-like protein 1 (PIWIL1) plays a crucial role in stem cell proliferation, embryogenesis, growth, and development, as well as differentiation and maturation in multiple organisms. The relationships between PIWIL1 expression and clinicopathological features of colorectal cancer (CRC) patients were analyzed by us. Survival analysis was performed using the Kaplan-Meier method and Cox's proportional hazards model. The high expression rate of PIWIL1 in the cancer tissue was obviously higher than that in the corresponding adjacent tissue. The expression of PIWIL1 was closely related to the tumor differentiation degree, infiltration depth, lymphovascular invasion, lymph node metastasis, and TNM stage. The Kaplan-Meier survival model suggested that the survival time of CRC patients in the high PIWIL1 expression group was notably lower than that in the low PIWIL1 expression group. High PIWIL1 expression suggests a poor prognosis for CRC patients, and PIWIL1 can serve as an important molecular marker for predicting the prognosis of CRC patients.

PIWIL2 promotes progression of non-small cell lung cancer by inducing CDK2 and Cyclin A expression

Background

PIWI proteins have important roles in tumorigenesis due to their interaction with piRNAs. Recent studies suggest that PIWI proteins affect prognosis of various cancers.

Methods

In the present study, PIWI genes expression was assayed in non-small cell lung cancer (NSCLC). To determine the effects of PIWIL2 on NSCLC cells, overexpression and interference assays were performed using the A549 and H460 cell lines. The tumor formation model was performed to demonstrate the effects of PIWIL2 on tumor formation in vivo.

Results

PIWIL2 was increased both at the RNA and protein level in malignant cancer tissues compared with adjacent normal tissue. Moreover, increased PIWIL2 gene expression was negatively correlated with prognosis in NSCLC patients. Overexpression and interference of PIWIL2 promoted and depressed cell proliferation, respectively. Meanwhile, PIWIL2 interference arrested cells at the G2/M stage. In addition, we found that CDK2 and Cyclin A expression were correlated with PIWIL2 expression. Moreover, transfection of PIWIL2 promoted tumor growth in nude mice.

Conclusion

Our findings shed light on the function of PIWIL2 in NSCLC and suggest potential prognostic and therapeutic value.

Methylation of RASSF1A gene promoter and the correlation with DNMT1 expression that may contribute to esophageal squamous cell carcinoma

Background

Esophageal squamous cell carcinoma is one of the most common malignancies in the world. Studies have confirmed that there are many genes abnormally hypermethylated in esophageal squamous cell carcinoma. The objective is to detect methylation of the RASSF1A gene promoter and the expression of the DNA methyltransferase 1 (DNMT1) protein in esophageal cancer tissue and discuss their relationship with esophageal squamous cell carcinoma.

Methods

The CpG island methylation status of RASSF1A genes were analyzed in 100 cases of tumor specimens as well as their adjacent tissues which was used for methylation-specific polymerase chain reaction (MSP). The expression of DNMT1 protein was determined by immunohistochemistry. Difference between measurement data and categorical data was compared through analysis of t test and chi-square test. All the statistics were taken with a bilateral test. The difference was statistically significant (P < 0.05).

Results

The promoter methylation of the RASSF1A gene promoter has been detected in 45 out of 100 (45%) esophageal squamous carcinoma cases, while methylation of RASSF1A gene has been detected in 2 out of 100 adjacent normal tissues (2%). The RASSF1A gene promoter was highly methylated in cancer tissues, and there were significant differences between normal esophagus tissues and esophageal squamous carcinoma (P < 0.05). The expression of DNMT1 protein has been detected in 61 out of 100 (61%) esophageal squamous carcinoma cases, including 41 cases in the above 45 methylated samples of RASSF1A gene promoter, and none in adjacent tissues. DNMT1 proteins are highly expressed in cancer tissues, and there were significant differences (P < 0.05). In positive cases for methylation of RASSF1A, the DNMT1 protein had been detected in 41 out of 45 (91%), while in non-methylated cancer cases, 20 out of 55(36.3%), and the difference is significant (P < 0.05).

Conclusions

Esophageal squamous carcinoma tumorigenesis may be related with hypermethylation of DNMT1 and RASSF1A promoter CpG island due to their high expression and also their hypermethylation.