A functional yeast survival screen of tumor-derived cDNA libraries designed to identify anti-apoptotic mammalian oncogenes

Yeast cells can be killed upon expression of pro-apoptotic mammalian proteins. We have established a functional yeast survival screen that was used to isolate novel human anti-apoptotic genes overexpressed in treatment-resistant tumors. The screening of three different cDNA libraries prepared from metastatic melanoma, glioblastomas and leukemic blasts allowed for the identification of many yeast cell death-repressing cDNAs, including 28% of genes that are already known to inhibit apoptosis, 35% of genes upregulated in at least one tumor entity and 16% of genes described as both anti-apoptotic in function and upregulated in tumors. These results confirm the great potential of this screening tool to identify novel anti-apoptotic and tumor-relevant molecules. Three of the isolated candidate genes were further analyzed regarding their anti-apoptotic function in cell culture and their potential as a therapeutic target for molecular therapy. PAICS, an enzyme required for de novo purine biosynthesis, the long non-coding RNA MALAT1 and the MAST2 kinase are overexpressed in certain tumor entities and capable of suppressing apoptosis in human cells. Using a subcutaneous xenograft mouse model, we also demonstrated that glioblastoma tumor growth requires MAST2 expression. An additional advantage of the yeast survival screen is its universal applicability. By using various inducible pro-apoptotic killer proteins and screening the appropriate cDNA library prepared from normal or pathologic tissue of interest, the survival screen can be used to identify apoptosis inhibitors in many different systems

Long Non-Coding RNAs in Cancer and Development: Where Do We Go from Here?

Recent genome-wide expression profiling studies have uncovered a huge amount of novel, long non-protein-coding RNA transcripts (lncRNA). In general, these transcripts possess a low, but tissue-specific expression, and their nucleotide sequences are often poorly conserved. However, several studies showed that lncRNAs can have important roles for normal tissue development and regulate cellular pluripotency as well as differentiation. Moreover, lncRNAs are implicated in the control of multiple molecular pathways leading to gene expression changes and thus, ultimately modulate cell proliferation, migration and apoptosis. Consequently, deregulation of lncRNA expression contributes to carcinogenesis and is associated with human diseases, e.g., neurodegenerative disorders like Alzheimer’s Disease. Here, we will focus on some major challenges of lncRNA research, especially loss-of-function studies. We will delineate strategies for lncRNA gene targeting in vivo, and we will briefly discuss important consideration and pitfalls when investigating lncRNA functions in knockout animal models. Finally, we will highlight future opportunities for lncRNAs research by applying the concept of cross-species comparison, which might contribute to novel disease biomarker discovery and might identify lncRNAs as potential therapeutic targets

The Dark Side of the Epitranscriptome: Chemical Modifications in Long Non-Coding RNAs

The broad application of next-generation sequencing technologies in conjunction with improved bioinformatics has helped to illuminate the complexity of the transcriptome, both in terms of quantity and variety. In humans, 70–90% of the genome is transcribed, but only ~2% carries the blueprint for proteins. Hence, there is a huge class of non-translated transcripts, called long non-coding RNAs (lncRNAs), which have received much attention in the past decade. Several studies have shown that lncRNAs are involved in a plethora of cellular signaling pathways and actively regulate gene expression via a broad selection of molecular mechanisms. Only recently, sequencing-based, transcriptome-wide studies have characterized different types of post-transcriptional chemical modifications of RNAs. These modifications have been shown to affect the fate of RNA and further expand the variety of the transcriptome. However, our understanding of their biological function, especially in the context of lncRNAs, is still in its infancy. In this review, we will focus on three epitranscriptomic marks, namely pseudouridine (Ψ), N6-methyladenosine (m6A) and 5-methylcytosine (m5C). We will introduce writers, readers, and erasers of these modifications, and we will present methods for their detection. Finally, we will provide insights into the distribution and function of these chemical modifications in selected, cancer-related lncRNAs

The Cohesin Complex and Its Interplay with Non-Coding RNAs

The cohesin complex is a multi-subunit protein complex initially discovered for its role in sister chromatid cohesion. However, cohesin also has several other functions and plays important roles in transcriptional regulation, DNA double strand break repair, and chromosome architecture thereby influencing gene expression and development in organisms from yeast to man. While most of these functions rely on protein–protein interactions, post-translational protein, as well as DNA modifications, non-coding RNAs are emerging as additional players that facilitate and modulate the function or expression of cohesin and its individual components. This review provides a condensed overview about the architecture as well as the function of the cohesin complex and highlights its multifaceted interplay with both short and long non-coding RNAs

Noncoding RNA gene silencing through genomic integration of RNA destabilizing elements using zinc finger nucleases

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