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Abstract
Long intergenic noncoding RNAs are transcripts originating from the regions without annotated coding genes. They are located mainly in the nucleus and regulate gene expression. Long intergenic noncoding RNAs can be also found in the cytoplasm acting as molecular sponges of certain microRNAs. This is crucial in various biological and signaling pathways. Expression levels of many long intergenic noncoding RNAs are disease related. In this article, we focus on the long intergenic noncoding RNAs and their relation to different types of cancer. Studies showed that abnormal expression of long intergenic noncoding RNA deregulates signaling pathways due to the disrupted free microRNA pool. Hampered signaling pathways leads to abnormal cell proliferation and restricts cell death, thus resulting in oncogenesis. This review highlights promising therapeutic targets and enables the identification of potential biomarkers specific for a certain type of cancer. Moreover, we provide an outline of long intergenic noncoding RNAs/microRNA axes, which might be applied in further detailed experiments broadening our knowledge about the cellular role of those RNA species.
1Introduction
As much as 98% of the human genome does not encode proteins [1]. It was initially assumed that noncoding transcripts play no role, however, subsequent research has shown that noncoding RNAs provide an important source of knowledge that allows for a better understanding of cellular processes.
We can distinguish noncoding transcripts by length. Transcripts smaller than 200 nucleotides are called small noncoding RNAs; they include tRNAs, rRNAs, microRNAs (miRNAs), snoRNAs, and pi-RNAs. Long noncoding RNAs (lncRNAs) are noncoding RNAs longer than 200 nucleotides [2]. According to published studies, lncRNAs can be spliced and polyadenylated. These transcripts possess a 5' terminal cap structure, which is a characteristic of mRNAs [3]. The lncRNAs generally do not have coding potential because of the lack of both open reading frames and translation termination regions [4]. Long noncoding RNAs include intergenic, intronic, sense, and antisense transcripts [5].
Long intergenic noncoding RNAs (lincRNAs) were first observed because of the usage of tiling arrays for the analysis of genomic sequences, as transcripts derived from the regions without known protein coding genes [6]. Although recent findings revealed that some of them might be the source of micropeptides, for example, LINC01420 [7]. Long intergenic noncoding RNAs have a variable conservation pattern. Only a...