TLC1 RNA nucleo-cytoplasmic trafficking links telomerase biogenesis to its recruitment to telomeres

Abstract

The yeast telomerase holoenzyme, which adds telomeric repeats at the chromosome ends, is composed of the TLC1 RNA and the associated proteins Est1, Est2 and Est3. To study the biogenesis of telomerase in endogenous conditions, we performed fluorescent in situ hybridization on the native TLC1 RNA. We found that the telomerase RNA colocalizes with telomeres in G1-to S-phase cells. Strains lacking any one of the Est proteins accumulate TLC1 RNA in their cytoplasm, indicating that a critical stage of telomerase biogenesis could take place outside of the nucleus. We were able to demonstrate that endogenous TLC1 RNA shuttles between the nucleus and the cytoplasm, in association with the Crm1p exportin and the nuclear importins Mtr10p-Kap122p. Furthermore, nuclear retention of the TLC1 RNA is impaired in the absence of yKu70p, Tel1p or the MRX complex, which recruit telomerase to telomeres. Altogether, our results reveal that the nucleo-cytoplasmic trafficking of the TLC1 RNA is an important step in telomere homeostasis, and link telomerase biogenesis to its recruitment to telomeres.

Anthracyclines disrupt telomere maintenance by telomerase through inducing PinX1 ubiquitination and degradation

“…Two decades have passed since this enzyme was characterized, but as yet a specific inhibitor has not been discovered. On the other hand, researches have revealed that the process of telomere maintenance by telomerase in cancer cells involves multiple regulatory steps, such as biogenesis of the telomerase ribonucleoprotein complex and recruitment of telomerase onto telomeres, suggesting that interferences of these events, without the need of wiping out TA per se, can also display the same outcome as do the telomerase inhibitors (Collins, 2006;Bianchi and Shore, 2008;Gallardo et al, 2008). Most recently, we have demonstrated that the nucleolar protein PinX1 has a role in mediating telomerase association with telomeres in cancer cells, and that disruption of this PinX1-dependent telomerase/telomere recruitment pathway, for example, by PinX1 silencing, significantly shortens telomere lengths, inhibits tumorigenesis and also enhances their sensitivity to the cytotoxic effects of DNAdamaging reagents in telomerase-positive cancer cells.…”

A Genomewide Suppressor and Enhancer Analysis of cdc13-1 Reveals Varied Cellular Processes Influencing Telomere Capping in Saccharomyces cerevisiae

“…There are extensive interactions, described in BioGrid, between vesicular traffic genes and other types of cdc13-1 suppressors (supplemental Figure S3); hence mutations that alter vesicular trafficking may affect telomeres through multiple different pathways. It is interesting to note that transport of telomerase proteins and TLC1 RNA across the nuclear membrane is important for telomerase function (Teixeira et al 2002;Gallardo et al 2008) and that deletion of KAP122, required for import of TLC1 from the cytoplasm to the nucleus (Gallardo et al 2008), suppresses cdc13-1.…”

Replication of Telomeres and the Regulation of Telomerase

“…When assessing telomere association of telomerase by live-cell imaging, it seemed that the Tlc1 -Ku80 interaction might only promote a transient interaction with telomeres, whereas the stable interaction in late S phase is mediated by Cdc13 -Est1 (Gallardo et al 2011). The Ku-mediated stimulation of telomerase may also involve its role in nuclear accumulation of Tlc1, which is reduced in Kudeficient cells (Gallardo et al 2008;Pfingsten et al 2012). How Tel1 and Tbf1 promote the interaction of Cdc13 and Est1 and the preferential extension of the shortest telomeres is unclear.…”