Epi-miRNAs: Regulators of the Histone Modification Machinery in Human Cancer

Cancer is a leading cause of death and disability worldwide. Epigenetic deregulation is one of the most critical mechanisms in carcinogenesis and can be classified into effects on DNA methylation and histone modification. MicroRNAs are small noncoding RNAs involved in fine-tuning their target genes after transcription. Various microRNAs control the expression of histone modifiers and are involved in a variety of cancers. Therefore, overexpression or downregulation of microRNAs can alter cell fate and cause malignancies. In this review, we discuss the role of microRNAs in regulating the histone modification machinery in various cancers, with a focus on the histone-modifying enzymes such as acetylases, deacetylases, methyltransferases, demethylases, kinases, phosphatases, desumoylases, ubiquitinases, and deubiquitinases. Understanding of microRNA-related aberrations underlying histone modifiers in pathogenesis of different cancers can help identify novel therapeutic targets or early detection approaches that allow better management of patients or monitoring of treatment response.

Histone methyltransferase SET8 is regulated by miR-192/215 and induces oncogene-induced senescence via p53-dependent DNA damage in human gastric carcinoma cells

Gastric cancer (GC) is the most common cancer throughout the world. Despite advances of the treatments, detailed oncogenic mechanisms are largely unknown. In our previous study, we investigated microRNA (miR) expression profiles in human GC using miR microarrays. We found miR-192/215 were upregulated in GC tissues. Then gene microarray was implemented to discover the targets of miR-192/215. We compared the expression profile of BGC823 cells transfected with miR-192/215 inhibitors, and HFE145 cells transfected with miR-192/-215 mimics, respectively. SET8 was identified as a proposed target based on the expression change of more than twofold. SET8 belongs to the SET domain-containing methyltransferase family and specifically catalyzes monomethylation of H4K20me. It is involved in diverse functions in tumorigenesis and metastasis. Therefore, we focused on the contributions of miR-192/215/SET8 axis to the development of GC. In this study, we observe that functionally, SET8 regulated by miR-192/215 is involved in GC-related biological activities. SET8 is also found to trigger oncogene-induced senescence (OIS) in GC in vivo and in vitro, which is dependent on the DDR (DNA damage response) and p53. Our findings reveal that SET8 functions as a negative regulator of metastasis via the OIS-signaling pathway. Taken together, we investigated the functional significance, molecular mechanisms, and clinical impact of miR-192/215/SET8/p53 in GC.

CCND1, NOP14 and DNMT3B are involved in miR-502-5p-mediated inhibition of cell migration and proliferation in bladder cancer

OBJECTIVES

Downregulation of miR-502-5p has emerged as a critical factor in tumour progression in several cancers. Herein, we elucidated the role of miR-502-5p in bladder cancer.

MATERIALS AND METHODS

RT-qPCR was performed to examine the expression of miR-502-5p in bladder cancer. And DNA methylation analysis showed that epigenetic mechanisms may contribute to the downregulation of miR-502-5p. Then, wound-healing assay, transwell assay, colony formation assay, CCK8 assay and flow cytometry analysis were applied to evaluate the function of miR-502-5p in bladder cancer cell lines. Western blot was conducted to measure the protein levels of related genes. Furthermore, dual-luciferase reporter assay, in vivo tumorigenesis assay and immunohistochemical staining were also conducted as needed.

RESULTS

MiR-502-5p is frequently downregulated in BCa. Meanwhile, hypermethylation of CpG islands contributes to the downregulation of miR-502-5p. Functionally, overexpression of miR-502-5p inhibited cell proliferation and migration in vitro and repressed tumour growth in vivo. CCND1, DNMT3B and NOP14 were identified as direct targets of miR-502-5p. Interestingly, DNMT3B and miR-502-5p established a positive feedback loop in the regulation of bladder cancer. In addition, rescue experiments further validated the direct molecular interaction between miR-502-5p and its targets.

CONCLUSIONS

Our study proposed and demonstrated that the miR-502-5p-mediated regulatory network is critical in bladder cancer; this network may be useful in the development of more effective therapies against bladder cancer.

Association of an miR-502-binding site polymorphism in the 3'-untranslated region of SET8 with colorectal cancer

The histone methyltransferase SET8 is regulated by microRNA-502 through the binding site in its 3'-untranslated region, and the rs16917496 polymorphism at the miR-502-binding site in the SET8 gene has been implicated in a number of cancer types. The rs16917496 polymorphism including CC, CT and TT genotypes was analyzed in patients with colorectal cancer; the CC genotype was identified to be independently associated with longer post-operative survival times using multivariate analysis (relative risk, 2.406; 95% confidence interval, 1.017-5.691; P=0.046). In addition, decreased SET8 expression was associated with the SET8 CC genotype and longer survival times for patients with colorectal cancer. The results of the present study indicated that miR-502 mediates SET8 expression at least partly by altering the binding affinity between miR-502 and SET8 so as to modify the colorectal cancer outcome. The results indicate that SET8 may be a novel target for colorectal cancer therapy.

Persistent High Levels of miR-502-5p Are Associated with Poor Neurologic Outcome in Patients with Aneurysmal Subarachnoid Hemorrhage

OBJECTIVE

To investigate the temporal changes in miR-502-5p expression after aneurysmal subarachnoid hemorrhage (aSAH) and to find the time to peak level.

METHODS

We collected serum from patients with aSAH (n = 129) at various time points (1, 3, 7, and 14 days postevent) and healthy controls (n = 40) at the Department of Neurosurgery, The First Affiliated Hospital of Wannan Medical College, from May 1, 2015 to January 31, 2016. We measured expression levels of miR-502-5p by polymerase chain reaction. We used the 2-ΔCt method and calculated correlations among variables using Spearman rank correlation coefficient analysis. We used receiver operating characteristic curves to identify optimal levels of miR-502-5p for aSAH and multivariate logistic regression to analyze risk factors on the modified Rankin scale. We measured miR-502-5p expression at all 4 time points post-aSAH.

RESULTS

Levels rose moderately from day 1 to day 7, with a substantial decrease from day 7 to day 14. The peak was at day 7. Multivariate logistic regression revealed that higher miR-502-5p levels at 7 days were associated with a significantly high risk for poor outcome post-aSAH.

CONCLUSIONS

Our data suggest that persistent elevated levels of miR-502-5p participate in the development of aSAH and may help physicians to adjust therapy for aSAH.

A functional single nucleotide polymorphism of SET8 is prognostic for breast cancer

A single-nucleotide polymorphism (SNP) locus rs16917496 (T > C) within the 3′-untranslated region (3′-UTR) of SET8 was associated with susceptibility in several malignancies including breast cancer. To further elucidate the prognostic relevance of this SNP in breast cancer, we conducted a clinical study as well as SET8 expression analysis in a cohort of 1,190 breast cancer patients. We demonstrated the expression levels of SET8 in TT genotype were higher than in CC genotypes, and high levels of SET8 were associated with poor survival. SET8 expression was significantly higher in breast tumor tissue than in paired adjacent normal tissue. In addition, survival analysis in 315 patients showed SNP rs16917496 was an independent prognostic factor of breast cancer outcome with TT genotype associated with poor survival compared with CC/CT genotypes. Thus, this SNP may serve as a genetic prognostic factor and a treatment target for breast cancer. Future studies are warranted.

miR-502-mediated histone methyltransferase SET8 expression is associated with clear cell renal cell carcinoma risk

Genetic variants may affect the interactions between microRNAs (miRNAs/miRs) and their target genes by modulating their binding affinity or by creating, or destroying a miRNA-binding site. SET domain containing (lysine methyltransferase) 8 (SET8) is the sole lysine methyltransferase that catalyzes the monomethylation of histone H4 lysine 20, and is associated with tumor growth, invasion and metastasis. In the present study, the rs16917496 polymorphism within the miR-502 binding site of the SET8 mRNA 3' untranslated region (3'UTR) in patients with clear cell renal cell carcinoma (ccRCC) and healthy controls was genotyped. The SET8 CC genotype was associated with a decreased ccRCC risk compared with the CT [P=0.003; odds ratio (OR)=0.318; 95% confidence interval (CI), 0.146-0.691], TT (P=0.011; OR=0.402; 95% CI, 0.197-0.819) and CT+TT (P=0.004; OR=0.370; 95% CI, 0.186-0.736) genotypes. The SET8 CC genotype was associated with reduced SET8 expression based on immunostaining of ccRCC tissue. Low SET8 protein levels were negatively associated with tumor-node-metastasis staging in patients with ccRCC according to the size of tumor and lymph node metastases. SET8-knockdown inhibited renal carcinoma 786-O cell proliferation, migration and invasion. c-Myc and matrix metalloproteinase-7 mRNA expression were downregulated upon SET8-knockdown in renal carcinoma 786-O cells. These data indicated that SET8 may be a functional tumor promoter and that its activation, which is partially regulated by changing the miR-502 and SET8 3'UTR binding affinity, may serve an important role in ccRCC development.

Germline variation in the 3'-untranslated region of the POU2AF1 gene is associated with susceptibility to lymphoma

Genetic variations in certain genes may alter the susceptibility to lymphoma. We searched electronic databases and selected candidate single-nucleotide polymorphisms (SNPs) located within 3'-untranslated regions (3'-UTRs) that might affect miRNA-binding ability in the 50 most dysregulated genes in lymphoma for further study. We found that rs1042752-located in the 3'-UTR of POU2AF1, which plays a vital role in lymphomagenesis-was significantly associated with lymphoma risk in a case-control study with 793 patients and 939 controls. Compared with individuals with the rs1042752TT genotype, those with the rs1042752CC genotype had a higher risk of lymphoma (OR = 2.14, 95% CI: 1.55-2.95, P < 0.001), even in stratified analysis for non-Hodgkin lymphoma (OR = 4.58, 95% CI: 2.38-8.81, P < 0.001), B-cell lymphoma (OR = 4.89, 95% CI: 2.46-9.73, P < 0.001), T-cell lymphoma (OR = 4.20, 95% CI: 1.76-10.05, P = 0.001), and Hodgkin lymphoma (OR = 3.62, 95% CI: 1.25-10.46, P = 0.018). Similar results were also observed in a recessive genetic model. Database findings suggested that rs1042752 might affect the interaction of POU2AF1 mRNA with hsa-miR-633. Functional assays confirmed that rs1042752C altered the binding site of hsa-miR-633 and increased POU2AF1 expression in Ramos, HuT 102, and Jurkat E6-1 cell lines. These findings demonstrate for the first time that functional polymorphism in the 3'-UTR of POU2AF1 is associated with susceptibility, and that SNP interaction with hsa-miR-633 affects gene expression and increases the risk of lymphoma.

Dysregulated MicroRNA Expression Profiles and Potential Cellular, Circulating and Polymorphic Biomarkers in Non-Hodgkin Lymphoma

A large number of studies have focused on identifying molecular biomarkers, including microRNAs (miRNAs) to aid in the diagnosis and prognosis of the most common subtypes of non-Hodgkin lymphoma (NHL), Diffuse Large B-cell Lymphoma and Follicular Lymphoma. NHL is difficult to diagnose and treat with many cases becoming resistant to chemotherapy, hence the need to identify improved biomarkers to aid in both diagnosis and treatment modalities. This review summarises more recent research on the dysregulated miRNA expression profiles found in NHL, as well as the regulatory role and biomarker potential of cellular and circulating miRNAs found in tissue and serum, respectively. In addition, the emerging field of research focusing on miRNA single nucleotide polymorphisms (miRSNPs) in genes of the miRNA biogenesis pathway, in miRNA genes themselves, and in their target sites may provide new insights on gene expression changes in these genes. These miRSNPs may impact miRNA networks and have been shown to play a role in a host of different cancer types including haematological malignancies. With respect to NHL, a number of SNPs in miRNA-binding sites in target genes have been shown to be associated with overall survival.

miR-502 medaited histone methyltransferase SET8 expression is associated with outcome of esophageal squamous cell carcinoma

The histone methyltransferase SET8, whose expression is regulated by miR-502 though the binding site in the 3′ UTR of SET8, implicated in cancer development. Single nucleotide polymorphism (SNP) of rs16917496 located in the miR-502 and SET8 binding site was analyzed in esophageal squamous cell carcinoma (ESCC) patients, the SET8 C/C genotype was independently associated with longer post-operative survival by multivariate analysis (relative risk, 2.250; 95% CI, 1.041–4.857; p = 0.039). Moreover, the reduced SET8 expression mediated by SET8 C/C genotype was associated with longer ESCC survival. Functional assay indicated that the SET8 knock down could inhibit proliferation and promote apoptosis of ESCC cells. The subsequent assay also showed the markedly inhibition of ESCC cell migration and invasion by SET8 knock down. Our data suggested that the altering SET8 expression, which is mediated at least partly by miR-502 through changing the binding affinity between miR-502 and SET8 3′ UTR, could modify the ESCC outcome by inhibiting the proliferation and invasion as well as promoting the apoptosis of ECSS cell. Our data indicated that SET8 was a new target for ESCC therapy.

MiR-502/SET8 regulatory circuit in pathobiology of breast cancer

Our previous research and extensive epidemiological studies reproducibly demonstrated that miR-502 potentially targeted the expression of H4K20 methyltransferase SET8 in a wide spectrum of cancer. Yet, the direct targeting of SET8 by miR-502 has not been definitively proven. The clinical significance of the miR-502/SET8 regulatory circuit is also not clear. Here, we conducted cell-based experiments and clinical studies in a cohort of 279 breast cancer samples. We provide evidence that SET8 is a direct target of miR-502. Treatment with miR-502 or downregulation of SET8 suppressed cell proliferation and cell cycle, and reduced cell migration, invasion and EMT. Clinical analyses showed the miR-502 expression was lower in tumor tissues than in adjacent non-tumor tissues and had a significant inverse correlation with that of SET8. Furthermore, high expression of SET8 was significantly associated with poor overall survival (OS) and disease free survival (DFS) of breast cancer. The low expression ratio of miR-502 to SET8 mRNA was also significantly associated with poor OS. Thus, the miR-502/SET8 regulatory circuit emerges as a key regulator of the pathobiology of cancer and a focal point for possible therapeutic intervention.