KCNQ1 Opposite Strand/Antisense Transcript 1 (KCNQ1OT1) encodes a lncRNA from the opposite strand of KCNQ1 in the CDKN1C/KCNQ1OT1 cluster that is reported to play a vital role in the development and progression of cancer.
1. Basic Characteristics of Human Chromosome 11p15.5 and lncRNA KCNQ1OT1 Gene
KCNQ1 Opposite Strand/Antisense Transcript 1 (KCNQ1OT1), also known as KCNQ1 overlapping transcript 1, or LIT1, is a 91 kb un-spliced lncRNA located on chromosome 11p15.5 (
Figure 1). The KCNQ1OT1 gene is part of a cluster of genes that undergo genomic imprinting, an epigenetic modification involving parent-specific gene expression modification. Genomic imprinting plays a critical role in fetal growth and development and is regulated by a nearby region of DNA known as imprinting center 2 (IC2) or KvDMR, which undergoes differential methylation
[1][2]. The human CDKN1C/KCNQ1OT1 cluster exists as imprinted genes, expressing only one copy, with the allele activity depending on the parental origin. The paternally expressed KCNQ1OT1 transcript originates from intron 11 and is antisense to its associated protein-coding gene, Potassium Voltage-Gated Channel Subfamily Q Member 1 (KCNQ1)
[3][4][5][6]. The antisense lncRNA KCNQ1OT1 promoter maps to KCNQ1 imprinting control regions, methylated on the maternal chromosome but un-methylated on the paternal chromosome.
Figure 1. Schematic representation of imprinted gene clusters on human chromosome 11p15.5.
Genes located near the KCNQ1OT1 promoter (KCNQ1, CDKN1C, SLC22A18, and PHLDA2) that are imprinted both in the embryo and extra-embryonic tissues such as the placenta are ubiquitously imprinted genes, whereas the placental specific imprinted genes ASCL2, TSPAN32, CD81, TSSC4, and OSBPL5, and are only imprinted in the placenta (
Figure 1)
[7]. The ubiquitously expressed KCNQ1OT1 is more frequently localized in the nucleus, interacts with chromatin complexes, and regulates the genomic imprinting of multiple genes through bidirectional transcription-mediated silencing in cis
[6][8][9]. Thus, the DNA sequences of the KCNQ1 and KCNQ1OT1 genes are “read” in opposite directions and have very different functions. LncRNA KCNQ1OT1 is expressed in every tissue
[10] and regulates genes vital for normal growth and development before birth, as well as postnatal behavior
[6][11]. However, deletion of its promoter or early transcript termination results in a loss of KCNQ1OT1 and a disruption of imprinting in the CDKN1C/KCNQ1OT1 domain, which can lead to growth-related disorders (ex. Beckwith-Wiedemann syndrome) and cancer, as well as bi-allelic expression of the entire KCNQ1 domain
[12].
2. KCNQ1OT1 in Human Cancers
In the present review, we will explore current knowledge on the role of KCNQ1OT1 in the development of various human cancers. We will thoroughly discuss the molecular and mechanistic role of KCNQ1OT1 in modulating oncogenic and biological functions, regulating cancer cell signaling mechanisms, and describe how its expression correlates to clinical features (Table 1). The interaction of KCNQ1OT1 and miRNAs or/and proteins and the potential targets in different cancers are summarized in Figure 2.
Figure 2. Interactions between KCNQ1OT1 and miRNA/genes in different kinds of human cancers. KCNQ1OT1 can interact with various miRNAs and genes in different tumor types (a), including female-specific cancers (b). Created with BioRender.com.
Table 1. Functional characterization of lncRNA KCNQ1OT1 and its targets in various cancers.