Table 1 The classification of lncRNAs.
From: The role of lncRNA-mediated ceRNA regulatory networks in pancreatic cancer
Taxonomy | Species | Characteristics | References |
|---|---|---|---|
Genomic origins | Sense/antisense | Sense or antisense lncRNA locates within or overlaps with the exons of the associated protein-coding gene on the same or opposite strand, while antisense lncRNA transcribes in the opposite direction of protein-coding gene | [131] |
Bidirectional | Bidirectional lncRNA locates nearby the promoter of the associated protein-coding gene and transcribes in the opposite direction | [131] | |
Intronic | Intronic lncRNA arises from long introns and transcribes from inside of an intron of the associated protein-coding gene | [131] | |
Intergenic | Intergenic lncRNA originates from intergenic segment of two protein-coding genes | [131] | |
Function | rRNA | A major structural component of the ribosome that interacts with specific mRNA sequences. Prokaryotic rRNAs are 5 Sa, 16 S, and 23 S, while eukaryotic rRNAs are 5 S, 5.8 s, 18 S, and 28 S, of which 16 S, 23 S, 18 S, and 28 S are long non-coding RNAs | [132] |
cRNA | cRNAs interact with chromatin by the recruitment of the polycomb repressive complex (PRC) mostly. PRC induces chromatin modification, which leads to epigenetic gene silencing | ||
eRNA | eRNAs can increase the expression of target genes in cis by increasing the strength of the enhancer-promoter looping or impede the binding of negative elongation factors (NELFs) to the promoter thereby alleviating transcriptional repression | ||
SINEUP | SINEUPs are modular antisense lncRNAs with an inverted SINEB2 sequence and a small complementarity sequence of the targeted mRNA, which up-regulate the translation of mRNAs in a gene-specific manner without affecting gene expression | ||
ceRNA | ceRNAs as miRNA sponges compete with mRNAs for miRNA binding, thus impairing the biological activity of miRNA | ||
Subcellular localization | Nuclear lncRNA | Most of the nuclear lncRNAs are regulators of transcription, and they can both enhance or silence the transcription of genes by recruiting transcription factors or by acting as decoy impeding the binding of transcription factors to DNA | [142] |
Cytoplasmic lncRNA | Cytoplasmic lncRNAs are more commonly involved in post-transcriptional regulation | [142] | |
Mitochondrial lncRNA | The light strand of mitochondrial DNA codes one subunit of nicotinamide adenine dinucleotide dehydrogenase (ND), 8 tRNAs, and 3 lncRNAs, while these lncRNAs regulate ND5 (NADH dehydrogenase subunit 5), ND6 (NADH dehydrogenase subunit 6) and CYTB (cytochrome b) throughout complementary binding of respective RNAs. Moreover, mitochondrial DNA allows the synthesis of two lncRNAs (SncmtRNA and ASncmtRNA) related to cell proliferation or tumor suppression, while LIPCAR is associated with the risk of heart failure |
