The valine-arginine dipeptide repeat protein encoded by mammalian telomeric RNA appears highly expressed in mitosis and may repress global translation.

Translation of mammalian telomeric G-rich RNA via the Repeat Associated non-AUG translation mechanism can produce two dipeptide repeat proteins: repeating valine-arginine (VR) and repeating glycine-leucine (GL). Their potentially toxic nature suggests that one or both must play a needed role in the cell. Using light microscopy combined with antibody staining we discovered that cultured human cells stain brightly for VR during mitosis with VR staining co-localizing with ribosomes. In vitro , VR protein represses translation in a firefly luciferase assay. Affinity purification combined with mass spectrometry identified ribosomal proteins as the major class of VR interacting proteins. Extension to mouse embryonic cerebral cortical development showed strong staining in the ventricular zone where high mitotic index neural progenitor cells proliferate and in the cortical plate where new neurons settle. These observations point to VR playing a key role in mitosis very possibly depressing global translation, a role mediated by the telomere. Teaser: The telomeric valine-arginine dipeptide repeat protein is highly expressed in mitotic cells in culture and in mouse embryonic neural tissue.

Telomeric RNA (TERRA) increases in response to spaceflight and high-altitude climbing.

Telomeres are repetitive nucleoprotein complexes at chromosomal termini essential for maintaining genome stability. Telomeric RNA, or TERRA, is a previously presumed long noncoding RNA of heterogeneous lengths that contributes to end-capping structure and function, and facilitates telomeric recombination in tumors that maintain telomere length via the telomerase-independent Alternative Lengthening of Telomeres (ALT) pathway. Here, we investigated TERRA in the radiation-induced DNA damage response (DDR) across astronauts, high-altitude climbers, healthy donors, and cellular models. Similar to astronauts in the space radiation environment and climbers of Mt. Everest, in vitro radiation exposure prompted increased transcription of TERRA, while simulated microgravity did not. Data suggest a specific TERRA DDR to telomeric double-strand breaks (DSBs), and provide direct demonstration of hybridized TERRA at telomere-specific DSB sites, indicative of protective TERRA:telomeric DNA hybrid formation. Targeted telomeric DSBs also resulted in accumulation of TERRA foci in G2-phase, supportive of TERRA's role in facilitating recombination-mediated telomere elongation. Results have important implications for scenarios involving persistent telomeric DNA damage, such as those associated with chronic oxidative stress (e.g., aging, systemic inflammation, environmental and occupational radiation exposures), which can trigger transient ALT in normal human cells, as well as for targeting TERRA as a therapeutic strategy against ALT-positive tumors.

Mammalian telomeric RNA (TERRA) can be translated to produce valine-arginine and glycine-leucine dipeptide repeat proteins.

Mammalian telomeres consist of (TTAGGG)n repeats. Transcription of the C-rich strand generates a G-rich RNA, termed TERRA, containing G-quadruplex structures. Recent discoveries in several human nucleotide expansion diseases revealed that RNA transcripts containing long runs of 3 or 6 nt repeats which can form strong secondary structures can be translated in multiple frames to generate homopeptide or dipeptide repeat proteins, and multiple studies have shown them to be toxic in cells. We noted that the translation of TERRA would generate two dipeptide repeat proteins: highly charged repeating valine-arginine (VR)n and hydrophobic repeating glycine-leucine (GL)n. Here, we synthesized these two dipeptide proteins and raised polyclonal antibodies to VR. The VR dipeptide repeat protein binds nucleic acids and localizes strongly to replication forks in DNA. Both VR and GL form long 8-nm filaments with amyloid properties. Using labeled antibodies to VR and laser scanning confocal microscopy, threefold to fourfold more VR was observed in the nuclei of cell lines containing elevated TERRA as contrasted to a primary fibroblast line. Induction of telomere dysfunction via knockdown of TRF2 led to higher amounts of VR, and alteration of TERRA levels using a locked nucleic acid (LNA) GapmeR led to large nuclear VR aggregates. These observations suggest that telomeres, in particular in cells undergoing telomere dysfunction, may express two dipeptide repeat proteins with potentially strong biological properties.