MicroRNA, epigenetic machinery and lung cancer

Transcriptional regulation of nuclear miRNAs in tumorigenesis (Review)

MicroRNAs (miRNAs/miRs) are a type of endogenous non‑coding small RNA that regulates gene expression. miRNAs regulate gene expression at the post‑transcriptional level by targeting the 3'‑untranslated region (3'UTR) of cytoplasmic messenger RNAs (mRNAs). Recent research has confirmed the presence of mature miRNAs in the nucleus, which bind nascent RNA transcripts, gene promoter or enhancer regions, and regulate gene expression via epigenetic pathways. Some miRNAs have been shown to function as oncogenes or tumor suppressor genes by modulating molecular pathways involved in human cancers. Notably, a novel molecular mechanism underlying the dysregulation of miRNA expression in cancer has recently been discovered, indicating that miRNAs may be involved in tumorigenesis via a nuclear function that influences gene transcription and epigenetic states, elucidating their potential therapeutic implications. The present review article discusses the import of nuclear miRNAs, nucleus‑cytoplasm transport mechanisms and the nuclear functions of miRNAs in cancer. In addition, some software tools for predicting miRNA binding sites are also discussed. Nuclear miRNAs supplement miRNA regulatory networks in cancer as a non‑canonical aspect of miRNA action. Further research into this aspect may be critical for understanding the role of nuclear miRNAs in the development of human cancers.

MicroRNAs are involved in the development and progression of gastric cancer

MicroRNAs (miRNAs) are recognized as an essential component of the RNA family, exerting multiple and intricate biological functions, particularly in the process of tumorigenesis, proliferation, and metastatic progression. MiRNAs are altered in gastric cancer (GC), showing activity as both tumor suppressors and oncogenes, although their true roles have not been fully understood. This review will focus upon the recent advances of miRNA studies related to the regulatory mechanisms of gastric tumor cell proliferation, apoptosis, and cell cycle. We hope to provide an in-depth insight into the mechanistic role of miRNAs in GC development and progression. In particular, we summarize the latest studies relevant to miRNAs' impact upon the epithelial-mesenchymal transition, tumor microenvironment, and chemoresistance in GC cells. We expect to elucidate the molecular mechanisms involving miRNAs for better understanding the etiology of GC, and facilitating the development of new treatment regimens for the treatment of GC.

Reduced Kiss‑1 expression is associated with clinical aggressive feature of gastric cancer patients and promotes migration and invasion in gastric cancer cells

Gastric cancer (GC) causes high morbidity and mortality in patients largely due to its invasion and metastasis. Kiss‑1 has been shown to be a metastasis suppressor in various malignancies. However, its clinical significance and biological functions in GC have not been thoroughly investigated. The present study investigated the association between Kiss‑1 expression and its methylation status and clinicopathological features in GC. Kiss‑1 expression was reduced in GC and its low expression was associated with poor histological grade, lymph node metastasis and TNM III+IV stage. Kiss‑1 overexpression in AGS GC cells significantly inhibited cell proliferation, migration and invasion in vitro. Kiss‑1 knockdown promoted the proliferation, migration and invasion of HGC‑27 cells. In summary, the data demonstrated that a low expression of Kiss‑1 played a suppressive role for the proliferation, migration and invasion of GC cells. Its expression and methylation levels were associated with the clinical progression of GC. Thus, Kiss‑1 is a potential diagnostic and prognostic marker as well as a new target for the treatment of GC.

Upregulation of Insulin-Like Growth Factor-1 Receptor (IGF-1R) Reverses the Inhibitory Effect of Let-7g-5p on Migration and Invasion of Nasopharyngeal Carcinoma

Background

Let-7 microRNAs (miRNAs) have the effects of inhibiting tumor growth and metastasis, however, the research in nasopharyngeal carcinoma (NPC) is limited. This study focused on the effects of Let-7 on NPC migration and invasion and the mechanism of action.

Material/Methods

Plasmid transfection was used to upregulate the expression levels of Let-7g-5p and insulin-like growth factor-1 receptor (IGF-1R). Cell counting kit-8 (CCK-8) assay was applied to test the cell viability. Scratch assay and Transwell assay were performed to detect the migration and invasion abilities. Bioinformatics prediction and luciferase reporter assay were used to determine and verify the downstream target genes for Let-7g-5p. Protein and mRNA were detected by western blot and real-time quantitative polymerase chain reaction (RT-qPCR), respectively.

Results

Let-7g-5p was under-expressed in human NPC cells. Overexpression of Let-7g-5p could inhibit cell viability and inhibit the migration and invasion of SUNE1 cells. The dual-luciferase reporter assay showed that IGF-1R was a direct target gene of Let-7g-5p, which was directly regulated IGF-1R expression by 3′UTR. Let-7g-5p overexpression could inhibit the expression of IGF-1R gene, and upregulation of IGF-1R gene expression reversed the inhibitory effect of Let-7g-5p on cell viability and epithelial-mesenchymal transition processes.

Conclusions

Let-7g-5p is lowly expressed in NPC and it was the first to discover that IGF-1R was a target gene of let-7g-5p in NPC. Upregulation of IGF-1R reversed the inhibitory effect of Let-7g-5p on epithelial-mesenchymal transition.

Long non‑coding RNA NORAD promotes cell proliferation and glycolysis in non‑small cell lung cancer by acting as a sponge for miR‑136‑5p

NORAD (non-coding RNA activated by DNA damage) is a long non-coding RNA (lncRNA) that is upregulated and promotes cell progression in various human types of cancer; however, its function in non-small cell lung cancer (NSCLC) remains unclear. The present study investigated the regulatory function and underlying mechanisms of NORAD in NSCLC. NORAD and miR-136-5p expression were assessed by reverse transcription-quantitative polymerase chain reaction, and proliferation and glycolysis-associated markers were also assessed. Direct miR-136-5p regulation by NORAD was detected using luciferase reporter assay and RNA immunoprecipitation. NORAD was highly expressed in NSCLC tissues and cell lines. NORAD overexpression increased NSCLC proliferation and glycolysis. Further investigation revealed that NORAD serves as a competing endogenous RNA for miR-136-5p. Gain- and loss-of-function experiments confirmed that miR-136-5p reversed the promoting effects of NORAD in NSCLC. Results of the present study indicate that NORAD serves as a growth-promoting lncRNA in NSCLC by suppressing the function of miR-136-5p. NORAD and miR-136-5p interaction may provide a potential target for NSCLC treatment.

Long non-coding RNA OIP5-AS1 promotes proliferation of lung cancer cells and leads to poor prognosis by targeting miR-378a-3p

Background

The antisense of the OIP5‐AS1 gene is a long non‐coding RNA (lncRNA) that is reported to be upregulated and promotes cell proliferation in multiple human cancers; however, its function in lung cancer is unknown. We investigated the regulatory function and underlying mechanisms of OIP5‐AS1 in lung cancer.

Methods

OIP5‐AS1 and microRNA (miR)‐378a‐3p expression were assayed by quantitative real‐time PCR, and proliferation‐related protein expression was measured by Western blotting. Cell viability was detected using methyl thiazolyl tetrazolium assay. Luciferase reporter assay and RNA immunoprecipitation were used to detect the direct regulation of miR‐378a‐3p by OIP5‐AS1. Nude mice were used to test the function of OIP5‐AS1 in vivo.

Results

OIP5‐AS1 was highly expressed in lung cancer tissues and was correlated with tumor size and tumor growth speed. OIP5‐AS1 overexpression increased lung cancer cell proliferation in vitro. Further investigation revealed that OIP5‐AS1 functions as a competing endogenous RNA of miR‐378a‐3p. MiR‐378a‐3p overexpression inhibited cell proliferation and caused proliferation‐associated proteins CDK4 and CDK6 to decrease in A549 cells. Overexpression of wild type OIP5‐AS1 led to strong CDK4 and CDK6 expression; however, these two proteins did not change when mutated OIP5‐AS1 was upregulated. Finally, in vivo assay showed that the speed of tumor growth was increased and decreased when OIP5‐AS1 was upregulated and downregulated, respectively.

Conclusion

Our results revealed that OIP5‐AS1 acts as a growth‐promoting lncRNA in lung cancer by suppressing miR‐378a‐3p function. OIP5‐AS1 and miR‐378a‐3p interaction may provide a potential target for lung cancer treatment.

A new insight on reciprocal relationship between microRNA expression and epigenetic modifications in human lung cancer

Lung cancer stands among the leading causes of cancer-related death in the world. Although the molecular network implicated in lung cancer development is extensively revealed, the mortality rate is only slightly improved. MicroRNAs are small, endogenous single-stranded evolutionary conserved non-coding RNAs which involve in a wide variety of biological processes including cell growth, proliferation, metabolism, and differentiation. MicroRNAs, as novel biomarkers, have multiple functions in normal lung tissue development, and aberrant expression profiles of certain microRNAs could induce lung tumorigenesis. Similar to that of protein-coding genes, microRNA expression and function are regulated by multiple factors as well as the epigenetic network including DNA methylation and histone modification mechanisms. Furthermore, microRNAs can themselves regulate key enzymes which drive epigenetic modifications and have a pivotal effect on the cell biology. In this review, we will look into the regulatory loop linkage between microRNA expression and epigenetic modifications, and then, we will discuss the effects of epigenetics on the miRNome, as well as the role of epi-microRNAs in controlling the epigenome in human lung cancer. Better knowledge of reciprocal connection between microRNAs and epigenome will help to develop novel microRNA-orientated diagnostic, prognostic and therapeutic strategies related to human lung cancer in future.

The new concepts on overcoming drug resistance in lung cancer

Lung cancer is one of the most deadly diseases worldwide. The current first-line therapies include chemotherapy using epidermal growth factor receptor tyrosine kinase inhibitors and radiotherapies. With the current progress in identifying new molecular targets, acquired drug resistance stands as an obstacle for good prognosis. About half the patients receiving epidermal growth factor receptor-tyrosine kinase inhibitor treatments develop resistance. Although extensive studies have been applied to elucidate the underlying mechanisms, evidence is far from enough to establish a well-defined picture to correct resistance. In the review, we will discuss four different currently developed strategies that have the potential to overcome drug resistance in lung cancer therapies and facilitate prolonged anticancer effects of the first-line therapies.

Promoter methylation and expression of TIMP3 gene in gastric cancer

Background

Gastric carcinoma development is a multi-stage process that involves more than one gene. Aberrant changes in DNA methylation are considered as the third mechanism that leads to anti-oncogene inactivation, which plays an essential role in tumor development. In this study, we assessed the relationship among the aberrant methylation of the promoter CpG islands of tissue inhibitor of metalloproteinase 3 (TIMP3) gene, its protein expression, and the clinicopathological features of gastric adenocarcinoma.

Methods

The methylation status of the promoter CpG islands and the protein expression of TIMP3 gene in tumors and adjacent normal mucosal tissues of 78 patients with gastric adenocarcinoma were detected by methylation-specific PCR (MSP) and immunohistochemistry.

Results

The CpG island methylation of TIMP3 was detected in tumor tissues, cancer-adjacent tissues, and lymph nodes with metastasis. In increasing order, the hypermethylation frequency of these tissues were 35.9% (28 of 78 non-neoplastic tissues), 85% (17 of 20 early-stage cases), 89.7% (52 of 58 progressive-stage cases), and 100% (78 of 78 metastatic lymph node). A marked difference was found between tumors and non-neoplastic tissues (P < 0.05), but no difference existed among the subgroups of tumors (P > 0.05). Immunohistochemistry analysis confirmed TIMP3 down-regulation in tumor tissues. The rate of TIMP3 gene expression was 100% in non-neoplastic tissues but apparently decreased to various extents at different stages, i.e., decreased to 30% (6/20) at the early stage, to 3.4% (2/58) at the progressive stage, and to 0% (0/78) in metastatic lymph nodes. Among the 70 tumor tissues with negative TIMP3 expression, 64 (91.4%) were hypermethylated and 6 were unmethylated (8.6%), indicating a significant association between hypermethylation and reduced or negative TIMP3 expression (P < 0.01).

Conclusion

The hypermethylation of the promoter region in CpG islands is the main mechanism of TIMP3 gene expression and may provide evidence for the molecular diagnosis and stage evaluation of gastric cancer.

Virtual slides

The virtual slides for this article can be found here: http://www.diagnosticpathology.diagnomx.eu/vs/1756134016954958

The expression patterns of Msi1 related with the glioma grade and the cytoplasmic Msi1 promotes angiogenesis

To investigate the expression patterns of Msi1 and its relationship with tumour grading and angiogenesis in human glioma. Msi1 expression and the angiogenesis labelled by CD31 were detected by immunohistochemical staining in glioma from Grade I to Grade IV. MVD-CD31 was counted respectively in nuclear and cytoplasmic positive areas of Msi1. There was weak expression of Msi1 in the adjacent normal brain tissue of glioma, and there were less MVD-CD31 than in glioma. Glioma showed strong expression and different patterns of Msi1. From Grade I to Grade IV glioma, the expression pattern of Msi1 was changed from nuclear into cytoplasmic pattern gradually (P<0.05), and the expression patterns of Msi1 were related with the angiogenesis of glioma (P<0.05). It suggested that cytoplasmic Msi1 promoted angiogenesis and nuclear Msi-1 inhibited angiogenesis in glioma (P<0.05). Msi1 has different expression patterns in glioma from Grade I to Grade IV, and the different expression patterns play diverse roles in angiogenesis of glioma. This might explain that from Grade I to IV, glioma showed worse and worse prognosis.

Screening and identification of lung cancer metastasis-related genes by suppression subtractive hybridization

BACKGROUND AND OBJECTIVE

  Lung cancer metastasis is a complicated process in which multiple stages and multiple genes are involved. There is an urgent need to use new molecular biology techniques to get more systematic information and have a general idea of the molecular events that take place in lung cancer metastasis. The object of this study was to construct the subtracted cDNA libraries of different metastatic potential lung cancer cell lines, NL9980 and L9981, which were established and screened from human lung large cell carcinoma cell line, WCQH-9801.

METHOD

  The forward and reverse subtracted cDNA libraries were constructed in the large cell lung cancer cell lines NL9980 and L9981 with the same heredity background but different metastatic potential, by suppression subtractive hybridization (SSH). The positive clones were preliminarily screened by blue-white colony and precisely identified by PCR. The forward and reverse subtracted libraries were screened and identified by dot blot so as to obtain the clones corresponding to gene segments with differential expression. DNA sequencing was performed to analyze the sequences of differential expression segments, which were then searched and compared using the Basic Local Alignment Search Tool from The National Center for Biotechnology Information NCBI BLAST tools. Quantitative real-time reverse transcription polymerase chain reaction (RT-PCR) and western blotting were performed to confirm the differential expressed genes both on RNA and protein levels.

RESULTS

  The forward and reverse subtracted cDNA libraries of the different large cell lung cancer cell lines with metastatic potential were successfully constructed. With blue-white colony and dot blot, 307 positive clones in the forward subtracted library and 78 positive clones in the reverse subtracted library were obtained. Fifty-five clones were successfully sequenced in the forward subtracted library while 31 clones were successfully sequenced in the reverse subtracted library. One new expressed sequence tag (EST) segment was identified from the reverse subtracted cDNA library and was successfully submitted to GenBank and embodied by GenBank. For the differentially expressed genes between L9981 and NL9980 screened by SSH, four genes, ANXA2, KRT18, ACTG1 was upregulated in L9981 cells compared to NL9980 cells. Annexin A2 (which was encoded by ANXA2), γ-actin (which was encoded by ACTG1), and aldose reductase (which was encoded by AKR1B1) proteins were upregulated in L9981 cells compared to NL9980 cells by western blotting.

CONCLUSION

  The forward and reverse subtracted cDNA libraries of different metastatic potential large cell lung cancer cell lines were successfully constructed by SSH. A series of genes have been screened out to have significantly different expression levels between lung cancer cell lines NL9980 and L9981. A new EST segment that may represent a new metastasis-related gene has been identified. Consistent with the result of SSH, both quantitative real-time RT-PCR and western Blotting confirmed the upregulation of ANXA2, ACTG1 and AKR1B1 in lung cancer cell line L9981 compared with NL9980. These three genes may play important roles in lung cancer metastasis.