Noncoding human Y RNAs are overexpressed in tumours and required for cell proliferation

Abstract

Noncoding Y RNAs have recently been identified as essential factors for chromosomal DNA replication in human cell nuclei. Here, we investigate the expression of human Y RNAs in tumours and test their requirement for cell proliferation. Relative expression levels of all four human Y RNAs (hY1, hY3, hY4 and hY5 RNA) were determined by quantitative RT -PCR in extracts from human solid tumours, corresponding nonmalignant normal tissues and derived cultured cells. On average, all four hY RNAs are significantly overexpressed in solid tumours between 4-and 13-fold, compared to the corresponding normal tissues. In particular, hY1 and hY3 RNAs are overexpressed in carcinomas (and adenocarcinomas) of the bladder, cervix, colon, kidney, lung and prostate with extremely high statistical significance (ANOVA, between groups, Po10e-22). A functional requirement of all four hY RNAs for cell proliferation was investigated in a systematic survey for loss-of-function by RNA interference (RNAi). Degradation of hY1 and hY3 RNAs in human cell lines resulted in a significant cytostatic inhibition of cell proliferation. We conclude that noncoding hY RNAs have potential both as new cancer biomarkers and as molecular targets for anti-proliferative intervention.

A conserved motif of vertebrate Y RNAs essential for chromosomal DNA replication

“…7). We have shown before that RNA interference against hY1 or hY3 RNA in proliferating human cells significantly reduces the proportions of S phase cells (Christov et al 2006(Christov et al , 2008. Transfection of control siRNA against a nontarget RNA (firefly luciferase mRNA) did not reduce the proportion of S phase cells, and a second transfection 2 h later of either wt or mutant hY1 RNAs had no significant effect (Fig.…”

“…The execution point for Y RNA function has been identified as the initiation stage of DNA replication, and not the chain elongation stage (Krude et al 2009). A functional requirement of hY RNAs for DNA replication has also been found in cell-based systems as degradation of hY1 or hY3 RNAs in proliferating human cells in culture reduces the proportion of replicating cells in the treated cell population (Christov et al 2006(Christov et al , 2008. The replication-specific function of hY RNAs is independent of their ability to bind to Ro60 protein as mutational inactivation of the Ro60 binding site of hY1 RNA does not inactivate its activity to promote chromosomal DNA replication (Christov et al 2006).…”

“…An evolutionary history of these genes has been deduced in two recent computational analyses of genomic sequence data (Mosig et al 2007;Perreault et al 2007). In this scenario, a common vertebrate Y RNA ancestor first split into pre-Y1/Y3 and pre-Y4/Y5 genes, which have then split further into the four extant (Christov et al 2008), 100 nM of the indicated wild-type and mutant Y RNAs were transfected into the same cells. At 23 h after RNAi, replicating cells in the population were labeled with BrdU for 1 h. At 24 h, percentages of S phase cells incorporating BrdU into their chromosomal DNA were determined by immunofluorescence microscopy.…”

“…We have recently identified an essential function for human Y RNAs during chromosomal DNA replication (Christov et al 2006(Christov et al , 2008. In eukaryotes, chromosomal DNA replication is initiated at many replication origins in each cell nucleus (Gilbert 2001;Machida et al 2005;Costa and Blow 2007).…”

Noncoding RNAs: Different roles in tumorigenesis

“…Many other ncRNAs including Alu RNA [75], Y RNA [76], and small nucleolar RNA [77], show abnormal expression patterns in cancerous tissues. Their roles and possible mechanisms are not reviewed here; however, some details about them are described in the references.…”