Long non-coding RNAs – Messages from the dark matter of the cancer genome


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Sven Diederichs1
1University of Freiburg and German Cancer Research Center (DKFZ)

Abstract

The majority of the human genome is transcribed into non-protein-coding RNA. Hence, RNA is also the primary product of the cancer genome. We have defined the ncRNA expression landscape of lung, breast and liver cancer providing a comprehensive expression map of over 17000 long ncRNAs and discovering new lncRNAs associated with cancer whose molecular and cellular functions we are currently elucidating exploiting our custom siRNA library targeting 638 tumor-associated lncRNAs. The nuclear lncRNA MALAT1 was one of the first lncRNAs associated with cancer: it is associated with metastasis development in lung cancer. However, its high abundance and nuclear localization have hampered its functional analysis. To uncover its functional importance, we developed a MALAT1 knockout model in human lung tumor cells by genomically integrating RNA destabilizing elements site-specifically into the MALAT1 locus. This approach yielded a 1000-fold silencing of MALAT1 providing a unique loss-of-function model. Proposed mechanisms of MALAT1 action include regulation of splicing or gene expression.

In lung cancer, MALAT1 does not alter alternative splicing but regulates gene expression inducing a signature of metastasis-associated genes. Consequently, MALAT1-deficient cells are impaired in migration and form fewer tumor nodules in a mouse xenograft model. Encouraged by this discovery of the essential function of MALAT1 in lung cancer metastasis, we analyzed whether MALAT1 could serve as therapeutic target for an Antisense oligonucleotide (ASO). Notably, MALAT1-ASO treatment prevented metastasis formation after tumor implantation. Thus, targeting MALAT1 with ASOs provided a therapeutic approach to prevent lung cancer metastasis with MALAT1 serving as both, predictive marker and therapeutic target. In summary, ten years after the discovery of the lncRNA MALAT1 as a biomarker for lung cancer metastasis, our loss-of-function model unraveled the active function of MALAT1 as a regulator of gene expression governing hallmarks of lung cancer metastasis.

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