Abstract
The fundamental function of ribonucleic acids is to transfer genetic information from DNA to protein during translation process, however, this is not the only way connecting active RNA sequences with essential biological processes. Up until now, many RNA subclasses of different size, structure, and biological function were identified. Among them, there are non-coding single-stranded microRNAs (miRNAs). This subclass comprises RNAs of 19–25 nucleotides in length that modulate the activity of well-defined coding RNAs and play a crucial role in many physiological and pathological processes. miRNA genes are located both in exons, introns, and also within non-translated regions. Several miRNAs that are transcribed from the adjacent miRNA genes are called cluster. One of the largest ones is miR-17-92 cluster known as OncomiR-1 due to its strong link to oncogenesis. Six miRNAs from the OncomiR-1 have been shown to play important roles in various physiological cellular processes but also through inhibition of cell death in many cancer-relevant processes. Due to the origin and similarity of the sequence, miR-17-92 cluster and paralogs, miR-106b-25 and miR-106a-363 clusters were defined. Here we discuss the oncogenic function of those miRNA subgroups found in many types of cancers, including brain tumors.
Highlights
About 80% of the human genome is transcribed but only up to 2% of it comprises protein coding sequences
Analysis of miR-19a, miR-92, and miR-20a in pediatric MBs showed increased expression levels in SHH-activated MBs in comparison to those showing a lack of SHH pathway activation [67]. These results indicated for miR-17-92 cluster significance during MB formation driven by an aberrant SHH pathway and suggested a functional relationship between those molecular factors
The role of non-coding sequences including miR-17-92, miR-106b-25, and miR-106a-363 clusters was documented in many cancers
Summary
About 80% of the human genome is transcribed but only up to 2% of it comprises protein coding sequences. Within the group of non-coding RNAs there are some sequences which are expressed constitutively They participate in basic processes related to gene expression and play an important role in proper functioning of the cell. Genes for miRNAs are often organized in clusters that are transcribed as polycistronic transcription units They may exist between protein coding sequences where acting as standalone transcription units and can be found in exons, introns, and untranslated regions [8]. Because of their extensive role in gene regulation, miRNAs are involved in many cellular processes, such as proliferation, development, differentiation, apoptosis, and tumor growth [7,9]. It was suggested that the miR-106a-363 cluster is regulated by the MITF (microphthalmia-associated transcription factor) located in the cluster’s immediate vicinity [43]
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