Gene Co-Expression Analysis of Human RNASEH2A Reveals Functional Networks Associated with DNA Replication, DNA Damage Response, and Cell Cycle Regulation.

Ribonuclease (RNase) H2 is a key enzyme for the removal of RNA found in DNA-RNA hybrids, playing a fundamental role in biological processes such as DNA replication, telomere maintenance, and DNA damage repair. RNase H2 is a trimer composed of three subunits, RNASEH2A being the catalytic subunit. RNASEH2A expression levels have been shown to be upregulated in transformed and cancer cells. In this study, we used a bioinformatics approach to identify RNASEH2A co-expressed genes in different human tissues to underscore biological processes associated with RNASEH2A expression. Our analysis shows functional networks for RNASEH2A involvement such as DNA replication and DNA damage response and a novel putative functional network of cell cycle regulation. Further bioinformatics investigation showed increased gene expression in different types of actively cycling cells and tissues, particularly in several cancers, supporting a biological role for RNASEH2A but not for the other two subunits of RNase H2 in cell proliferation. Mass spectrometry analysis of RNASEH2A-bound proteins identified players functioning in cell cycle regulation. Additional bioinformatic analysis showed that RNASEH2A correlates with cancer progression and cell cycle related genes in Cancer Cell Line Encyclopedia (CCLE) and The Cancer Genome Atlas (TCGA) Pan Cancer datasets and supported our mass spectrometry findings.

SAM68 is required for regulation of Pumilio by the NORAD long noncoding RNA.

The number of known long noncoding RNA (lncRNA) functions is rapidly growing, but how those functions are encoded in their sequence and structure remains poorly understood. NORAD (noncoding RNA activated by DNA damage) is a recently characterized, abundant, and highly conserved lncRNA that is required for proper mitotic divisions in human cells. NORAD acts in the cytoplasm and antagonizes repressors from the Pumilio family that bind at least 17 sites spread through 12 repetitive units in NORAD sequence. Here we study conserved sequences in NORAD repeats, identify additional interacting partners, and characterize the interaction between NORAD and the RNA-binding protein SAM68 (KHDRBS1), which is required for NORAD function in antagonizing Pumilio. These interactions provide a paradigm for how repeated elements in a lncRNA facilitate function.

RNA takes over control of DNA break repair.

Small RNAs generated at DNA break sites are implicated in mammalian DNA repair. Now, a study shows that following the formation of DNA double-strand breaks, bidirectional transcription events adjacent to the break generate small RNAs that trigger the DNA damage response by local RNA:RNA interactions.

A conserved abundant cytoplasmic long noncoding RNA modulates repression by Pumilio proteins in human cells.

Thousands of long noncoding RNA (lncRNA) genes are encoded in the human genome, and hundreds of them are evolutionarily conserved, but their functions and modes of action remain largely obscure. Particularly enigmatic lncRNAs are those that are exported to the cytoplasm, including NORAD-an abundant and highly conserved cytoplasmic lncRNA. Here we show that most of the sequence of NORAD is comprised of repetitive units that together contain at least 17 functional binding sites for the two mammalian Pumilio homologues. Through binding to PUM1 and PUM2, NORAD modulates the mRNA levels of their targets, which are enriched for genes involved in chromosome segregation during cell division. Our results suggest that some cytoplasmic lncRNAs function by modulating the activities of RNA-binding proteins, an activity which positions them at key junctions of cellular signalling pathways.

Excitotoxic and Radiation Stress Increase TERT Levels in the Mitochondria and Cytosol of Cerebellar Purkinje Neurons.

Telomerase reverse transcriptase (TERT) is the catalytic subunit of telomerase, an enzyme that elongates telomeres at the ends of chromosomes during DNA replication. Recently, it was shown that TERT has additional roles in cell survival, mitochondrial function, DNA repair, and Wnt signaling, all of which are unrelated to telomeres. Here, we demonstrate that TERT is enriched in Purkinje neurons, but not in the granule cells of the adult mouse cerebellum. TERT immunoreactivity in Purkinje neurons is present in the nucleus, mitochondria, and cytoplasm. Furthermore, TERT co-localizes with mitochondrial markers, and immunoblot analysis of protein extracts from isolated mitochondria and synaptosomes confirmed TERT localization in mitochondria. TERT expression in Purkinje neurons increased significantly in response to two stressors: a sub-lethal dose of X-ray radiation and exposure to a high glutamate concentration. While X-ray radiation increased TERT levels in the nucleus, glutamate exposure elevated TERT levels in mitochondria. Our findings suggest that in mature Purkinje neurons, TERT is present both in the nucleus and in mitochondria, where it may participate in adaptive responses of the neurons to excitotoxic and radiation stress.

Telomerase activity and expression in adult human mesenchymal stem cells derived from amyotrophic lateral sclerosis individuals.

BACKGROUND AIMS: Telomerase is a ribonucleoprotein that maintains the length of telomeres, and thus controls the proliferation and lifespan of cells. Recent studies suggest the involvement of telomerase in the protection of cells from apoptosis. Adult human mesenchymal stromal cells (hMSC) possess the capacity to proliferate and differentiate into a variety of cell types. hMSC derived from a healthy donor lack telomerase activity but their expression has not been investigated in hMSC derived from diseased adults. Cell replacement therapy using adult hMSC has been suggested as a promising therapeutic approach for amyotrophic lateral sclerosis (ALS). Therefore, we characterized the telomerase activity and expression in hMSC derived from bone marrow (BM) of ALS patients and compared them with those derived from a healthy donor. METHODS: Telomerase activity was examined with a TRAP assay and real-time polymerase chain reaction telomerase quantification assay. Telomerase protein was detected by Western blot and immunofluorescence analysis, and telomerase RNA transcripts were identified by Northern blot. RESULTS: Telomerase activity, telomerase enzyme protein and telomerase RNA transcripts were demonstrated in hMSC derived from ALS, but were undetectable in hMSC from the healthy donor. Telomerase activity in the hMSC of ALS patients was 106-fold lower compared with tumor cells. CONCLUSIONS: The detection of telomerase expression in hMSC derived from ALS patients and not a healthy donor suggests a possible role for telomerase in the response of hMSC to the disease. The presence of telomerase expression did not impair the ability of the ALS hMSC to differentiate, suggesting the use of these cells for cytotherapy treatments.