The hallmarks of cancer Gutschner, Tony; Diederichs, Sven
RNA biology,
06/2012, Volume:
9, Issue:
6
Journal Article
Peer reviewed
Open access
With the advent of next generation sequencing methods and progress in transcriptome analysis, it became obvious that the human genome contains much more than just protein-coding genes. In fact, up to ...70% of our genome is transcribed into RNA that does not serve as templates for proteins. In this review, we focus on the emerging roles of these long non-coding RNAs (lncRNAs) in the field of tumor biology. Long ncRNAs were found to be deregulated in several human cancers and show tissue-specific expression. Functional studies revealed a broad spectrum of mechanisms applied by lncRNAs such as HOTAIR, MALAT1, ANRIL or lincRNA-p21 to fulfill their functions. Here, we link the cellular processes influenced by long ncRNAs to the hallmarks of cancer and therefore provide an ncRNA point-of-view on tumor biology. This should stimulate new research directions and therapeutic options considering long ncRNAs as novel prognostic markers and therapeutic targets.
The
metastasis-associated lung adenocarcinoma transcript 1
(
MALAT1
) is a bona fide long noncoding RNA (lncRNA).
MALAT1
, also known as
nuclear-enriched transcript 2 (NEAT2)
, was discovered as a ...prognostic marker for lung cancer metastasis but also has been linked to several other human tumor entities. Recent work established a critical regulatory function of this lncRNA in lung cancer metastasis and cell migration. Moreover,
MALAT1
is an interesting target for antimetastatic therapy in non-small cell lung carcinoma. Two alternative modes of action have been proposed for
MALAT1
: regulation of gene expression or alternative splicing. Although the exact mechanism of action in different physiological and pathological conditions still needs to be elucidated,
MALAT1
acts as a regulator of gene expression. Although
MALAT1
is highly evolutionary conserved in mammals and plays an important role in cancer and metastasis,
MALAT1
is not essential for development in a knockout mouse model under normal physiological conditions. Hence, one central question for the future is finding the right stressor and the pathological or environmental condition which requires
MALAT1
expression in vivo and entailing its strong evolutionary conservation. Here, we summarize the current knowledge about this important lncRNA. We introduce its discovery, biogenesis, and regulation and describe its known functions, mechanisms of action, and interaction partners.
Synonymous mutations have been viewed as silent mutations, since they only affect the DNA and mRNA, but not the amino acid sequence of the resulting protein. Nonetheless, recent studies suggest their ...significant impact on splicing, RNA stability, RNA folding, translation or co-translational protein folding. Hence, we compile 659194 synonymous mutations found in human cancer and characterize their properties. We provide the user-friendly, comprehensive resource for synonymous mutations in cancer, SynMICdb ( http://SynMICdb.dkfz.de ), which also contains orthogonal information about gene annotation, recurrence, mutation loads, cancer association, conservation, alternative events, impact on mRNA structure and a SynMICdb score. Notably, synonymous and missense mutations are depleted at the 5'-end of the coding sequence as well as at the ends of internal exons independent of mutational signatures. For patient-derived synonymous mutations in the oncogene KRAS, we indicate that single point mutations can have a relevant impact on expression as well as on mRNA secondary structure.
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.
MicroRNAs are small endogenous noncoding RNAs involved in posttranscriptional gene regulation. During microRNA biogenesis, Drosha and Dicer process the primary transcript (pri-miRNA) through a ...precursor hairpin (pre-miRNA) to the mature miRNA. The miRNA is incorporated into the RNA-Induced Silencing Complex (RISC) with Argonaute proteins, the effector molecules in RNA interference (RNAi). Here, we show that all Argonautes elevate mature miRNA expression posttranscriptionally, independent of RNase activity. Also, we identify a role for the RISC slicer Argonaute2 (Ago2) in cleaving the pre-miRNA to an additional processing intermediate, termed Ago2-cleaved precursor miRNA or ac-pre-miRNA. This endogenous, on-pathway intermediate results from cleavage of the pre-miRNA hairpin 12 nucleotides from its 3′-end. By analogy to siRNA processing, Ago2 cleavage may facilitate removal of the nicked passenger strand from RISC after maturation. The multiple roles of Argonautes in the RNAi effector phase and miRNA biogenesis and maturation suggest coordinate regulation of microRNA expression and function.
Zinc finger nucleases (ZFNs) allow site-specific manipulation of the genome. So far, the use of ZFNs to create gene knockouts has been restricted to protein-coding genes. However, ...non-protein-encoding RNAs (ncRNA) play important roles in the cell, although the functions of most ncRNAs are unknown. Here, we describe a ZFN-based method suited for the silencing of protein-coding and noncoding genes. This method relies on the ZFN-mediated integration of RNA destabilizing elements into the human genome, e.g., poly(A) signals functioning as termination elements and destabilizing downstream sequences. The biallelic integration of poly(A) signals into the gene locus of the long ncRNA MALAT1 resulted in a 1000-fold decrease of RNA expression. Thus, this approach is more specific and 300 times more efficient than RNA interference techniques. The opportunity to create a variety of loss-of-function tumor model cell lines in different cancer backgrounds will promote future functional analyses of important long noncoding RNA transcripts.
Highlights • Evolutionary conservation of long-noncoding RNAs (lncRNA) is multidimensional. • Sequence, structure, function, and syntenic expression add up to lncRNA conservation. • Human and mouse ...loss-of-function models reveal surprising differences and similarities.
The long noncoding RNA MALAT1 (metastasis-associated lung adenocarcinoma transcript 1), also known as MALAT-1 or NEAT2 (nuclear-enriched abundant transcript 2), is a highly conserved nuclear ...noncoding RNA (ncRNA) and a predictive marker for metastasis development in lung cancer. To uncover its functional importance, we developed a MALAT1 knockout model in human lung tumor cells by genomically integrating RNA destabilizing elements using zinc finger nucleases. The achieved 1,000-fold MALAT1 silencing provides a unique loss-of-function model. Proposed mechanisms of action include regulation of splicing or gene expression. In lung cancer, MALAT1 does not alter alternative splicing but actively regulates gene expression including a set of metastasis-associated genes. Consequently, MALAT1-deficient cells are impaired in migration and form fewer tumor nodules in a mouse xenograft. Antisense oligonucleotides (ASO) blocking MALAT1 prevent metastasis formation after tumor implantation. Thus, targeting MALAT1 with ASOs provides a potential therapeutic approach to prevent lung cancer metastasis with this ncRNA serving as both predictive marker and therapeutic target. Finally, regulating gene expression, but not alternative splicing, is the critical function of MALAT1 in lung cancer metastasis. In summary, 10 years after the discovery of the lncRNA MALAT1 as a biomarker for lung cancer metastasis, our loss-of-function model unravels the active function of MALAT1 as a regulator of gene expression governing hallmarks of lung cancer metastasis.
The RNase III enzyme Drosha is a key factor in microRNA (miRNA) biogenesis and as such indispensable for cellular homeostasis and developmental processes. Together with its co-factor DGCR8, it ...converts the primary transcript (pri-miRNA) into the precursor hairpin (pre-miRNA) in the nucleus. While the middle and the C-terminal domain are crucial for pri-miRNA processing and DGCR8 binding, the function of the N-terminus remains cryptic. Different studies have linked this region to the subcellular localization of Drosha, stabilization and response to stress. In this study, we identify alternatively spliced Drosha transcripts that are devoid of a part of the arginine/serine-rich (RS-rich) domain and expressed in a large set of human cells. In contrast to their expected habitation, we find two isoforms also present in the cytoplasm, while the other two isoforms reside exclusively in the nucleus. Their processing activity for pri-miRNAs and the binding to co-factors remains unaltered. In multiple cell lines, the endogenous mRNA expression of the Drosha isoforms correlates with the localization of endogenous Drosha proteins. The pri-miRNA processing efficiency is not significantly different between groups of cells with or without cytoplasmic Drosha expression. In summary, we discovered novel isoforms of Drosha with differential subcellular localization pointing toward additional layers of complexity in the regulation of its activity.
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