Figure 3.

Mechanisms of action of long noncoding RNAs (lncRNAs). Several studies have described different modes of action for the functioning of lncRNAs in different model systems. It has been suggested that the primary sequence, secondary structure, and genomic position with respect to coding genes (intragenic, exonic, intronic, or overlapping) decides the mode of action of lncRNAs. Some lncRNAs function as RNA decoys at the genetic level by directly scavenging transcription factors [101,102]. Competitive endogenous RNAs (ceRNAs) function at the post-transcriptional level by scavenging miRNA functional effectors and thereby limiting miRNA availability for their mRNA targets, and provide another level of post-transcriptional gene regulation [103–105]. Some lncRNAs act as ‘RNA scaffolds’ for regulatory protein binding, which can lead to chromatin remodelling [102,106]. Some other lncRNAs result in the generation of endogenous small interfering RNAs (endo-siRNAs) via Dicer-mediated cleavage in the cytoplasm and thus inhibit target mRNA expression. Some lncRNAs are known directly to modulate target mRNA expression levels by translational repression, transcriptional activation, modulation of splicing patterns, or degradation [107–109].