PRC2 regulates RNA polymerase III transcribed non-translated RNA gene transcription through EZH2 and SUZ12 interaction with TFIIIC complex

The choreography of chromatin in RNA polymerase III regulation

Regulation of eukaryotic gene expression involves a dynamic interplay between the core transcriptional machinery, transcription factors, and chromatin organization and modification. While this applies to transcription by all RNA polymerase complexes, RNA polymerase III (RNAPIII) seems to be atypical with respect to its mechanisms of regulation. One distinctive feature of most RNAPIII transcribed genes is that they are devoid of nucleosomes, which relates to the high levels of transcription. Moreover, most of the regulatory sequences are not outside but within the transcribed open chromatin regions. Yet, several lines of evidence suggest that chromatin factors affect RNAPIII dynamics and activity and that gene sequence alone does not explain the observed regulation of RNAPIII. Here we discuss the role of chromatin modification and organization of RNAPIII transcribed genes and how they interact with the core transcriptional RNAPIII machinery and regulatory DNA elements in and around the transcribed genes.

Two opposing gene expression patterns within ATRX aberrant neuroblastoma

Neuroblastoma is the most common extracranial solid tumor in children. A subgroup of high-risk patients is characterized by aberrations in the chromatin remodeller ATRX that is encoded by 35 exons. In contrast to other pediatric cancer where ATRX point mutations are most frequent, multi-exon deletions (MEDs) are the most frequent type of ATRX aberrations in neuroblastoma. 75% of these MEDs are predicted to produce in-frame fusion proteins, suggesting a potential gain-of-function effect compared to nonsense mutations. For neuroblastoma there are only a few patient-derived ATRX aberrant models. Therefore, we created isogenic ATRX aberrant models using CRISPR-Cas9 in several neuroblastoma cell lines and one tumoroid and performed total RNA-sequencing on these and the patient-derived models. Gene set enrichment analysis (GSEA) showed decreased expression of genes related to both ribosome biogenesis and several metabolic processes in our isogenic ATRX exon 2-10 MED model systems, the patient-derived MED models and in tumor data containing two patients with an ATRX exon 2-10 MED. In sharp contrast, these same processes showed an increased expression in our isogenic ATRX knock-out and exon 2-13 MED models. Our validations confirmed a role of ATRX in the regulation of ribosome homeostasis. The two distinct molecular expression patterns within ATRX aberrant neuroblastomas that we identified imply that there might be a need for distinct treatment regimens.

TFIIIC as a Potential Epigenetic Modulator of Histone Acetylation in Human Stem Cells

Regulation of histone acetylation dictates patterns of gene expression and hence cell identity. Due to their clinical relevance in cancer biology, understanding how human embryonic stem cells (hESCs) regulate their genomic patterns of histone acetylation is critical, but it remains largely to be investigated. Here, we provide evidence that acetylation of histone H3 lysine-18 (H3K18ac) and lysine-27 (H3K27ac) is only partially established by p300 in stem cells, while it represents the main histone acetyltransferase (HAT) for these marks in somatic cells. Our analysis reveals that whereas p300 marginally associated with H3K18ac and H3K27ac in hESCs, it largely overlapped with these histone marks upon differentiation. Interestingly, we show that H3K18ac is found at "stemness" genes enriched in RNA polymerase III transcription factor C (TFIIIC) in hESCs, whilst lacking p300. Moreover, TFIIIC was also found in the vicinity of genes involved in neuronal biology, although devoid of H3K18ac. Our data suggest a more complex pattern of HATs responsible for histone acetylations in hESCs than previously considered, suggesting a putative role for H3K18ac and TFIIIC in regulating "stemness" genes as well as genes associated with neuronal differentiation of hESCs. The results break ground for possible new paradigms for genome acetylation in hESCs that could lead to new avenues for therapeutic intervention in cancer and developmental diseases.

A unique 15-bp InDel in the first intron of BMPR1B regulates its expression in Taihu pigs

BACKGROUND

BMPR1B (Bone morphogenetic protein receptor type-1B) is a receptor in the bone morphogenetic protein (BMP) family and has been identified as a candidate gene for reproductive traits in pigs. Our previous study in Taihu pigs found a specific estrogen response element (ERE) in the first intron of the BMPR1B gene that is associated with the number born alive trait. However, little is known about the mechanism by which the ERE regulates the expression of BMPR1B in the endometrium.

RESULTS

Here, a 15-bp InDel (insertion/deletion) (AGCCAGAAAGGAGGA) was identified as a unique variation in Taihu pigs, and was shown to be responsible for the binding of the type I receptor of estrogen (ESR1) to the ERE using dual-luciferase assays. Four BMPR1B transcripts (T1, T2, T3, and T4) were identified by 5' RACE in endometrial tissue. Expression of T3 and T4 in the endometrium of Meishan pigs was significantly higher than in Duroc pigs during pregnancy. Luciferase assays showed that three distinct BMPR1B promoters may drive expression of T1, T3, and T4. Interestingly, ERE-mediated enhancement of T4 promoter activity significantly increased expression of Transcript T4 in the endometrium of Taihu pigs (P < 0.05). In contrast, the ERE inhibited activity of the T3 promoter and decreased expression of the T3 transcript in the Duroc background (P < 0.05). In summary, we identified a 15-bp InDel in the Taihu ERE that can be used as a molecular marker for the number born alive trait, characterized the 5' untranslated regions (UTRs) of BMPR1B transcripts in the endometrium, and determined how the transcripts are processed by alternative splicing events.

CONCLUSIONS

Our results provide a foundation for understanding the transcriptional regulation of BMPR1B and its contributions to the unique breeding prolificacy characteristics of Taihu pigs.

Signal Recognition Particle in Human Diseases

The signal recognition particle (SRP) is a ribonucleoprotein complex with dual functions. It co-translationally targets proteins with a signal sequence to the endoplasmic reticulum (ER) and protects their mRNA from degradation. If SRP is depleted or cannot recognize the signal sequence, then the Regulation of Aberrant Protein Production (RAPP) is activated, which results in the loss of secretory protein mRNA. If SRP recognizes the substrates but is unable to target them to ER, they may mislocalize or degrade. All these events lead to dramatic consequence for protein biogenesis, activating protein quality control pathways, and creating pressure on cell physiology, and might lead to the pathogenesis of disease. Indeed, SRP dysfunction is involved in many different human diseases, including: congenital neutropenia; idiopathic inflammatory myopathy; viral, protozoal, and prion infections; and cancer. In this work, we analyze diseases caused by SRP failure and discuss their possible molecular mechanisms.

Epigenetic regulation of human non-coding RNA gene transcription

Recent investigations on the non-protein-coding transcriptome of human cells have revealed previously hidden layers of gene regulation relying on regulatory non-protein-coding (nc) RNAs, including the widespread ncRNA-dependent regulation of epigenetic chromatin states and of mRNA translation and stability. However, despite its centrality, the epigenetic regulation of ncRNA genes has received relatively little attention. In this mini-review, we attempt to provide a synthetic account of recent literature suggesting an unexpected complexity in chromatin-dependent regulation of ncRNA gene transcription by the three human nuclear RNA polymerases. Emerging common features, like the heterogeneity of chromatin states within ncRNA multigene families and their influence on 3D genome organization, point to unexplored issues whose investigation could lead to a better understanding of the whole human epigenomic network.

Elucidation of the BMI1 interactome identifies novel regulatory roles in glioblastoma

Glioblastoma (GBM) is the most common and aggressive intrinsic brain tumour in adults. Epigenetic mechanisms controlling normal brain development are often dysregulated in GBM. Among these, BMI1, a structural component of the Polycomb Repressive Complex 1 (PRC1), which promotes the H2AK119ub catalytic activity of Ring1B, is upregulated in GBM and its tumorigenic role has been shown in vitro and in vivo. Here, we have used protein and chromatin immunoprecipitation followed by mass spectrometry (MS) analysis to elucidate the protein composition of PRC1 in GBM and transcriptional silencing of defining interactors in primary patient-derived GIC lines to assess their functional impact on GBM biology. We identify novel regulatory functions in mRNA splicing and cholesterol transport which could represent novel targetable mechanisms in GBM.

HMGA1 promotes gastric cancer growth and metastasis by transactivating SUZ12 and CCDC43 expression

HMGA1 protein is an architectural transcription factor that has been implicated in the progression of multiple malignant tumors. However, the role of HMGA1 in the growth and metastasis of gastric cancer (GC) has not yet been elucidated. Here, we show that HMGA1 is overexpressed in GC cells and the high expression of HMGA1 was correlated with worse survival in GC patients using a bioinformatics assay. Functionally, HMGA1 affected the EdU incorporation, colony formation, migration and invasion of GC cells by exogenously increasing or decreasing the expression of HMGA1. Mechanistically, HMGA1 directly bound to the SUZ12 and CCDC43 promoter and transactivated its expression in GC cells. Inhibition of SUZ12 and CCDC43 attenuated the proliferation, migration and invasiveness of HMGA1-overexpressing GC cells in vitro. Moreover, both HMGA1 and SUZ12/CCDC43 were highly expressed in cancer cells but not in normal gastric tissues, and their expressions were positively correlated. Finally, a tail vein metastatic assay showed that HMGA1 promoted SUZ12/CCDC43-mediated GC cell metastasis in vivo. Our findings suggest that HMGA1 promotes GC growth and metastasis by transactivating SUZ12 and CCDC43 expression, highlighting HMGA1 as a potential prognostic biomarker in the treatment of GC.

Epigenetic regulation of protein translation in KMT2A-rearranged AML

Inhibition of the H3K79 histone methyltransferase DOT1L has exhibited encouraging preclinical and early clinical activity in KMT2A (MLL)-rearranged leukemia, supporting the development of combinatorial therapies. Here, we investigated two novel combinations: dual inhibition of the histone methyltransferases DOT1L and EZH2, and the combination with a protein synthesis inhibitor. EZH2 is the catalytic subunit in the polycomb repressive complex 2 (PRC2), and inhibition of EZH2 has been reported to have preclinical activity in KMT2A-r leukemia. When combined with DOT1L inhibition, however, we observed both synergistic and antagonistic effects. Interestingly, antagonistic effects were not due to PRC2-mediated de-repression of HOXA9. HOXA cluster genes are key canonical targets of both KMT2A and the PRC2 complex. The independence of the HOXA cluster from PRC2 repression in KMT2A-r leukemia thus affords important insights into leukemia biology. Further studies revealed that EZH2 inhibition counteracted the effect of DOT1L inhibition on ribosomal gene expression. We thus identified a previously unrecognized role of DOT1L in regulating protein production. Decreased translation was one of the earliest effects measurable after DOT1L inhibition and specific to KMT2A-rearranged cell lines. H3K79me2 chromatin immunoprecipitation sequencing patterns over ribosomal genes were similar to those of the canonical KMT2A-fusion target genes in primary AML patient samples. The effects of DOT1L inhibition on ribosomal gene expression prompted us to evaluate the combination of EPZ5676 with a protein translation inhibitor. EPZ5676 was synergistic with the protein translation inhibitor homoharringtonine (omacetaxine), supporting further preclinical/clinical development of this combination. In summary, we discovered a novel epigenetic regulation of a metabolic process-protein synthesis-that plays a role in leukemogenesis and affords a combinatorial therapeutic opportunity.

RREB1-induced upregulation of the lncRNA AGAP2-AS1 regulates the proliferation and migration of pancreatic cancer partly through suppressing ANKRD1 and ANGPTL4

Long noncoding RNAs (lncRNAs) have been reported to be involved in a variety of human diseases, including cancers. However, their mechanisms have not yet been fully elucidated. We investigated lncRNA changes that may be associated with pancreatic cancer (PC) by analyzing published microarray data, and identified AGAP2-AS1 as a relatively overexpressed lncRNA in PC tissues. qRT-PCR assays were performed to examine expression levels of AGAP2-AS1. MTT assays, colony formation assays, and EdU assays were used to determine the proliferative capacity of cells. Flow cytometry and TUNEL assays were used to study the regulation of AGAP2-AS1 in the cell cycle and apoptosis. Transwell experiments were used to study changes in cell invasion and metastasis, and a nude mouse model was established to assess the effects of AGAP2-AS1 on tumorigenesis in vivo. RNA sequencing was performed to probe AGAP2-AS1-related pathways. Subcellular fractionation and FISH assays were used to determine the distribution of AGAP2-AS1 in PC cells, and RIP and ChIP were used to determine the molecular mechanism of AGAP2-AS1-mediated regulation of potential target genes. Increased expression of AGAP2-AS1 was associated with tumor size and pathological stage progression in patients with PC. RREB1 was found to activate transcription of AGAP2-AS1 in PC cells. AGAP2-AS1 affected proliferation, apoptosis, cycle arrest, invasion, and metastasis of PC cells in vitro, and AGAP2-AS1 regulated PC proliferation in vivo. Furthermore, AGAP2-AS1 epigenetically inhibited the expression of ANKRD1 and ANGPTL4 by recruiting zeste homolog 2 (EZH2), thereby promoting PC proliferation and metastasis. In summary, our data show that RREB1-induced upregulation of AGAP2-AS1 regulates cell proliferation and migration in PC partly through suppressing ANKRD1 and ANGPTL4 by recruiting EZH2. AGAP2-AS1 represents a potential target for the diagnosis and treatment of PC in the future.

Long non‑coding RNA MLK7‑AS1 promotes proliferation in human colorectal cancer via downregulation of p21 expression

Current studies have highlighted long non‑coding RNAs (lncRNAs) as critical regulators in various cancers, including colorectal cancer (CRC). By utilizing publicly available data from The Cancer Genome Atlas dataset, MLK7 antisense RNA 1 (MLK7‑AS1) was identified as a novel lncRNA that correlated with CRC progression. The results of reverse transcription‑quantitative polymerase chain reaction (RT‑qPCR) revealed a significant upregulation of MLK7‑AS1 in both CRC tissue samples and cell lines. In addition, a positive correlation was observed between increased MLK7‑AS1 expression and several clinicopathological factors in patients with CRC. Importantly, MLK7‑AS1 knockdown suppressed CRC cell proliferation and promoted G1/G0 phase arrest and apoptosis in vitro, whereas MLK7‑AS1 overexpression exhibited opposite effects. Consistently, decreased MLK7‑AS1 expression inhibited tumor growth in vivo. Furthermore, RT‑qPCR and western blot assays revealed that p21 may be a potential downstream target of MLK7‑AS1. To the best of the authors' knowledge, this is the first study to report that MLK7‑AS1 has potential as a biomarker and may promote proliferation in CRC partially through downregulating p21 expression.

A Novel lncRNA, LINC00460, Affects Cell Proliferation and Apoptosis by Regulating KLF2 and CUL4A Expression in Colorectal Cancer

Emerging evidence has proven that long noncoding RNAs (lncRNAs) play important roles in human colorectal cancer (CRC) biology, although few lncRNAs have been characterized in CRC. Therefore, the functional significance of lncRNAs in the malignant progression of CRC still needs to be further explored. In this study, through analyzing TCGA RNA sequencing data and other publicly available microarray data, we found a novel lncRNA, LINC00460, whose expression was significantly upregulated in CRC tissues compared to adjacent normal tissues. Consistently, real-time qPCR results also verified that LINC00460 was overexpressed in CRC tissues and cells. Furthermore, high LINC00460 expression levels in CRC specimens were correlated with larger tumor size, advanced tumor stage, lymph node metastasis and shorter overall survival. In vitro and in vivo assays of LINC00460 alterations revealed a complex integrated phenotype affecting cell growth and apoptosis. Mechanistically, LINC00460 repressed Krüppel-like factor 2 (KLF2) transcription by binding to enhancer of zeste homolog 2 (EZH2). LINC00460 also functioned as a molecular sponge for miR-149-5p, antagonizing its ability to repress cullin 4A (CUL4A) protein translation. Taken together, our findings support a model in which the LINC00460/EZH2/KLF2 and LINC00460/miR-149-5p/CUL4A crosstalk serve as critical effectors in CRC tumorigenesis and progression, suggesting new therapeutic directions in CRC.

Current advances of long non-coding RNA highly upregulated in liver cancer in human tumors

Long non-coding RNAs (lncRNAs) are a group of non-coding RNAs (ncRNAs) >200 nucleotides in length that govern diverse biological processes. Recent evidence suggests that lncRNAs are involved in cancer cell proliferation, apoptosis, invasion, migration, and metastasis. Dysregulation of lncRNAs has been observed in various tumors, and lncRNAs act as oncogenes or tumor suppressors in these malignancies. It has been revealed that lncRNA highly upregulated in liver cancer (HULC) is tightly correlated with a number of cancers such as hepatocellular carcinoma, gastric cancer, colorectal cancer, osteosarcoma, and diffuse large B-cell lymphoma. Depletion of HULC suppressed cancer cell proliferation, migration, and invasion and induced apoptosis. Additionally, HULC may function as a diagnostic biomarker and prognostic indicator for some tumors. In this review, we summarize the current knowledge of the role of HULC in cancer progression and the clinical management of human cancers.

Epigenetic regulation of noncoding RNA transcription by mammalian RNA polymerase III

RNA polymerase III (Pol III) synthesizes a range of medium-sized noncoding RNAs (collectively 'Pol III genes') whose early established biological roles were so essential that they were considered 'housekeeping genes'. Besides these fundamental functions, diverse unconventional roles of mammalian Pol III genes have recently been recognized and their expression must be exquisitely controlled. In this review, we summarize the epigenetic regulation of Pol III genes by chromatin structure, histone modification and CpG DNA methylation. We also recapitulate the association between dysregulation of Pol III genes and diseases such as cancer and neurological disorders. Additionally, we will discuss why in-depth molecular studies of Pol III genes have not been attempted and how nc886, a Pol III gene, may resolve this issue.

Structure of the PRC2 complex and application to drug discovery

The polycomb repressive complexes 2 (PRC2) complex catalyzes tri-methylation of histone H3 lysine 27 (H3K27), a repressive chromatin marker associated with gene silencing. Overexpression and mutations of PRC2 are found in a wide variety of cancers, making the catalytic activity of PRC2 an important target of cancer therapy. This review highlights recent structural breakthroughs of the human PRC2 complex bound to the H3K27 peptide and a small molecule inhibitor, which provide critically needed insight into PRC2-targeted drug discovery.

TUG1: a pivotal oncogenic long non-coding RNA of human cancers

Long non-coding RNAs (lncRNAs) are a group greater than 200 nucleotides in length. An increasing number of studies has shown that lncRNAs play important roles in diverse cellular processes, including proliferation, differentiation, apoptosis, invasion and chromatin remodelling. In this regard, deregulation of lncRNAs has been documented in human cancers. TUG1 is a recently identified oncogenic lncRNA whose aberrant upregulation has been detected in different types of cancer, including B-cell malignancies, oesophageal squamous cell carcinoma, bladder cancer, hepatocellular carcinoma and osteosarcoma. In these malignancies, knock-down of TUG1 has been shown to suppress cell proliferation, invasion and/or colony formation. Interestingly, TUG1 has been found to be downregulated in non-small cell lung carcinoma, indicative of its tissue-specific function in tumourigenesis. Pertinent to clinical practice, TUG1 may act as a prognostic biomarker for tumours. In this review, we summarize current knowledge concerning the role of TUG1 in tumour progression and discuss mechanisms associated with it.