Genome-wide analysis of c-MYC-regulated mRNAs and miRNAs, and c-MYC DNA binding by next-generation sequencing

Germinal Centre B Cell Functions and Lymphomagenesis: Circuits Involving MYC and MicroRNAs

BACKGROUND

The transcription factor MYC regulates several biological cellular processes, and its target gene network comprises approximately 15% of all human genes, including microRNAs (miRNAs), that also contribute to MYC regulatory activity. Although miRNAs are emerging as key regulators of immune functions, the specific roles of miRNAs in the regulation/dysregulation of germinal centre B-cells and B-cell lymphomas are still being uncovered. The regulatory network that integrates MYC, target genes and miRNAs is a field of intense study, highlighting potential pathways to be explored in the context of future clinical approaches.

METHODS

The scientific literature that is indexed in PUBMED was consulted for publications involving MYC and miRNAs with validated bioinformatics analyses or experimental protocols. Additionally, seminal studies on germinal centre B-cell functions and lymphomagenesis were reported.

CONCLUSIONS

This review summarizes the interactions between MYC and miRNAs through regulatory loops and circuits involving target genes in germinal centre B-cell lymphomas with MYC alterations. Moreover, we provide an overview of the understanding of the regulatory networks between MYC and miRNAs, highlighting the potential implication of this approach for the comprehension of germinal centre B-cell lymphoma pathogenesis. Therefore, circuits involving MYC, target genes and miRNAs provide novel insight into lymphomagenesis that could be useful for new improved therapeutic strategies.

New Insight into microRNA Functions in Cancer: Oncogene-microRNA-Tumor Suppressor Gene Network

Tumorigenesis is a multi-step and complex process with multi-factors involved. Deregulated oncogenes and tumor suppressor genes (TSGs) induced by genetic and epigenetic factors are considered as the driving force in the development and progression of cancer. Besides, microRNAs (miRNAs) act vital roles in tumorigenesis through regulating some oncogenes and TSGs. Interestingly, miRNAs are also regulated by oncogenes and TSGs. Considering the entangled regulation, here we propose a new insight into these regulation relationships in cancer: oncogene–miRNA–TSG network, which further emphasizes roles of miRNA, as well as highlights the network regulation among oncogene, miRNA, and TSG during tumorigenesis. The oncogene–miRNA–TSG network demonstrates that oncogenes and TSGs not only show functional synergy, but also there are regulatory relationships among oncogenes and TSGs during tumorigenesis, which could be mediated by miRNAs. In view of the oncogene–miRNA–TSG network involved in many oncogenes, miRNAs, and TSGs, as well as occurring in various tumor types, the anomaly of this network may be a common event in cancers and participates in tumorigenesis. This hypothesis broadens horizons of molecular mechanisms underlying tumorigenesis, and may provide a new promising venue for the prediction, diagnosis, and even therapy of cancer.

Long non-coding RNA MINCR promotes gallbladder cancer progression through stimulating EZH2 expression

The regulation of MYC-regulated long non-coding RNAs has been reported to contribute to certain types of cancers. However, the role of MYC-induced long non-coding RNA (MINCR) in the tumorigenesis of gallbladder cancer (GBC) is still largely unknown. In this study, we discovered that MINCR was markedly upregulated in GBC tissues compared with adjacent normal tissues. High MINCR expression levels in GBC were positively associated with tumor volume and lymph node metastasis and were negatively correlated with overall survival (OS). Upregulation of MINCR and enhancer of zeste homolog 2 (EZH2) in GBC coincided with the downregulation of miR-26a-5p in GBC. Mechanistically, MINCR/miR-26a-5p/EZH2 axis was found to be involved in cell proliferation, cell invasive and apoptosis in GBC cells. Moreover, knockdown of MINCR suppressed cell proliferation, decreased S-phase cell numbers, increased cell apoptosis, and inhibited cell invasion by inhibiting the epithelial-mesenchymal transition (EMT) phenomenon in GBC cells. In vivo, tumor volumes were significantly decreased in the MINCR silencing group compared with those in the control group. These results demonstrated that MINCR could potentially be a therapeutic target as well as a prognostic marker in GBC.

The Quest for Targets Executing MYC-Dependent Cell Transformation

MYC represents a transcription factor with oncogenic potential converting multiple cellular signals into a broad transcriptional response, thereby controlling the expression of numerous protein-coding and non-coding RNAs important for cell proliferation, metabolism, differentiation, and apoptosis. Constitutive activation of MYC leads to neoplastic cell transformation, and deregulated MYC alleles are frequently observed in many human cancer cell types. Multiple approaches have been performed to isolate genes differentially expressed in cells containing aberrantly activated MYC proteins leading to the identification of thousands of putative targets. Functional analyses of genes differentially expressed in MYC-transformed cells had revealed that so far more than 40 upregulated or downregulated MYC targets are actively involved in cell transformation or tumorigenesis. However, further systematic and selective approaches are required for determination of the known or yet unidentified targets responsible for processing the oncogenic MYC program. The search for critical targets in MYC-dependent tumor cells is exacerbated by the fact that during tumor development, cancer cells progressively evolve in a multistep process, thereby acquiring their characteristic features in an additive manner. Functional expression cloning, combinatorial gene expression, and appropriate in vivo tests could represent adequate tools for dissecting the complex scenario of MYC-specified cell transformation. In this context, the central goal is to identify a minimal set of targets that suffices to phenocopy oncogenic MYC. Recently developed genomic editing tools could be employed to confirm the requirement of crucial transformation-associated targets. Knowledge about essential MYC-regulated genes is beneficial to expedite the development of specific inhibitors to interfere with growth and viability of human tumor cells in which MYC is aberrantly activated. Approaches based on the principle of synthetic lethality using MYC-overexpressing cancer cells and chemical or RNAi libraries have been employed to search for novel anticancer drugs, also leading to the identification of several druggable targets. Targeting oncogenic MYC effector genes instead of MYC may lead to compounds with higher specificities and less side effects. This class of drugs could also display a wider pharmaceutical window because physiological functions of MYC, which are important for normal cell growth, proliferation, and differentiation would be less impaired.

Identification of microRNA targets by pulsed SILAC

Pulsed stable isotope labeling by amino acids in cell culture (pulsed SILAC or pSILAC) allows to monitor and quantify the de novo synthesis of proteins in an unbiased fashion on a proteome-wide scale. The high applicability of this metabolic labeling technique has been demonstrated for the identification of posttranscriptional changes in gene expression on the proteome level, in particular those caused by microRNAs. The application of pSILAC allows the selective quantification of newly synthesized proteins and thus the detection of differences in protein translation. This is of particular interest in the case of microRNA-mediated regulations, which characteristically cause rather modest decreases in protein amounts that may be difficult to detect by other proteomic methods. Here, we describe a detailed protocol for using pSILAC to track miRNA-mediated changes in protein expression, using the p53-induced miR-34a microRNA as a prototypic example of microRNA-mediated regulations.