Minakshi Gandhi

Long intergenic non-coding RNA-Nucleotide Metabolism Regulator (lincNMR) is a long non-coding RNA (lncRNA) which is induced in hepatocellular carcinoma. Its depletion invokes a proliferation defect, triggers senescence and inhibits colony formation in liver, but also breast and lung cancer cells. Triple-label SILAC proteomics profiles reveal a deregulation of key cell cycle regulators in lincNMR-depleted cells like the key dNTP synthesizing enzymes RRM2, TYMS and TK1, implicating lincNMR in regulating nucleotide metabolism. LincNMR silencing decreases dNTP levels, while exogenous dNTPs rescues the proliferation defect induced by lincNMR depletion. In vivo RNA Antisense Purification (RAP-MS) identifies YBX1 as a direct interaction partner of lincNMR which regulates RRM2, TYMS and TK1 expression and binds to their promoter regions. In a Chick Chorioallantoic Membrane (CAM) in vivo model, lincNMR-depleted tumors are significantly smaller. In summary, we discover a lincRNA, lincNMR, which regulates tumor cell proliferation through a YBX1-RRM2-TYMS-TK1 axis governing nucleotide metabolism.

Although the number of documented noncoding RNAs (ncRNAs) is rapidly increasing, knowledge of their molecular function is lagging behind. The identification of specific RNA motifs that mediate transcript stability, interactions and localization may aid in the prediction of these features in new transcripts and may have potential implications for ncRNA function. Here, we review RNA motifs, focusing on four recent studies identifying nuclear-retention motifs, and discuss the limited specificity of short-RNA motifs and the resulting challenge for effective functional prediction. Future approaches may succeed by integrating combinatorial and cooperative effects of additional partially sequence-based properties.

Long non-coding RNAs (lncRNAs) have been proven to play important roles in diverse cellular processes including the DNA damage response. Nearly 40% of annotated lncRNAs are transcribed in antisense direction to other genes and have often been implicated in their regulation via transcript- or transcription-dependent mechanisms. However, it remains unclear whether inverse correlation of gene expression would generally point toward a regulatory interaction between the genes. Here, we profiled lncRNA and mRNA expression in lung and liver cancer cells after exposure to DNA damage. Our analysis revealed two pairs of mRNA-lncRNA sense-antisense transcripts being inversely expressed upon DNA damage. The lncRNA NOP14-AS1 was strongly upregulated upon DNA damage, while the mRNA for NOP14 was downregulated, both in a p53-dependent manner. For another pair, the lncRNA LIPE-AS1 was downregulated, while its antisense mRNA CEACAM1 was upregulated. To test whether as expected the antisense genes would regulate each other resulting in this highly significant inverse correlation, we employed antisense oligonucleotides and RNAi to study transcript-dependent effects as well as dCas9-based transcriptional modulation by CRISPRi/CRISPRa for transcription-dependent effects. Surprisingly, despite the strong stimulus-dependent inverse correlation, our data indicate that neither transcript- nor transcription-dependent mechanisms explain the inverse regulation of NOP14-AS1:NOP14 or LIPE-AS1:CEACAM1 expression. Hence, sense-antisense pairs whose expression is strongly—positively or negatively—correlated can be nonetheless regulated independently. This highlights the requirement of individual experimental studies for each antisense pair and prohibits drawing conclusions on regulatory mechanisms from expression correlations.

In recent years, long non-coding RNA (lncRNA) research has identified essential roles of these transcripts in virtually all physiological cellular processes including tumorigenesis, but their functions and molecular mechanisms are poorly understood. In this study, we performed a high-throughput siRNA screen targeting 638 lncRNAs deregulated in cancer entities to analyse their impact on cell division by using time-lapse microscopy. We identified 26 lncRNAs affecting cell morphology and cell cycle including LINC00152. This transcript was ubiquitously expressed in many human cell lines and its RNA levels were significantly upregulated in lung, liver and breast cancer tissues. A comprehensive sequence analysis of LINC00152 revealed a highly similar paralog annotated as MIR4435-2HG and several splice variants of both transcripts. The shortest and most abundant isoform preferentially localized to the cytoplasm. Cells depleted of LINC00152 arrested in prometaphase of mitosis and showed reduced cell viability. In RNA affinity purification (RAP) studies, LINC00152 interacted with a network of proteins that were associated with M phase of the cell cycle. In summary, we provide new insights into the properties and biological function of LINC00152 suggesting that this transcript is crucial for cell cycle progression through mitosis and thus, could act as a non-coding oncogene.