Mechanistic Roles of Noncoding RNAs in Lung Cancer Biology and Their Clinical Implications

Table 1

Classes of human non-coding RNAs.

Type	Class	Characteristics and function	References
Small ncRNA (<200 nt)	Small Interfering RNAs (siRNAs)	21-22 nt double-stranded RNAs produced by Dicer and involved in gene silencing and viral defence	[163]
	microRNAs (miRNAs)	18–25 nt RNAs that modulate gene expression posttranscriptionally	[163, 164]
	Transfer RNAs (tRNA)	An adaptor molecule with an inverted L structure involved in translation of mRNA into protein	[165]
	PIWI-interacting RNAs (piRNAs)	Dicer independent 26–31 nt RNAs located in the germline and adjacent somatic cells, involved in germline development and stability through the regulation of transposons	[163]
	Small nucleolar RNAs (snoRNAs)	Guide molecules for modification and processing of rRNA, specifically site-specific methylation and pseudouridylation	[164]
	microRNA-offset RNAs (moRNAs)	RNAs derived from the ends of pre-miRNAs, predominantly from the 5′ end, independent of the mature miRNA. The function of moRNAs are currently unknown	[16]
	Ribosomal 5.8S	Transcribed by pol I as a part of the 45S precursor, 5.8S is a component of the large ribosomal subunit in eukaryotes, and thus involved in protein translation	[166]
	Promoter-associated short RNAs (PASRs)	Transcripts within a few hundred bases of protein coding or noncoding transcription start site that may regulate gene expression	[167]
Long ncRNA (>200 nt)	Long ncRNA	A broad class of RNAs > 200 nt with functions in epigenetic regulation, splicing, and cellular localization	[40]
	Transcribed ultraconserved regions (T-UCR)	Non-coding sequences 100% conserved among humans, mice, and rats, with roles in the regulation of alternative splicing and gene expression, and altered in a number of human cancers	[168]
	Pseudogenes	Nonfunctional sequences of genomic DNA originally derived from functional genes but with mutations or premature stop codons that prevent their expression. Known to regulate gene expression and recombination	[161, 169]
	Promoter associated long RNAs (PARs)	Transcripts 250–500 nt long within a few hundred bases of protein coding or non coding transcription start sites that may regulate gene expression	[167]
	Antisense RNAs	Single stranded RNA complementary to a transcribed mRNA, capable of binding and blocking translation of its complementary mRNA, and promoting target decay.	[170]