Telomerase RNA TLC1 Shuttling to the Cytoplasm Requires mRNA Export Factors and Is Important for Telomere Maintenance

Abstract

Telomerases protect the ends of linear chromosomes from shortening. They are composed of an RNA (TLC1 in S. cerevisiae) and several proteins. TLC1 undergoes several maturation steps before it is exported into the cytoplasm to recruit the Est proteins for complete assembly. The mature telomerase is subsequently reimported into the nucleus, where it fulfills its function on telomeres. Here, we show that TLC1 export into the cytoplasm requires not only the Ran GTPase-dependent karyopherin Crm1/Xpo1 but also the mRNA export machinery. mRNA export factor mutants accumulate mature and export-competent TLC1 RNAs in their nuclei. Moreover, TLC1 physically interacts with the mRNA transport factors Mex67 and Dbp5/Rat8. Most importantly, we show that the nuclear export of TLC1 is an essential step for the formation of the functional RNA containing enzyme, because blocking TLC1 export in the mex67-5 xpo1-1 double mutant prevents its cytoplasmic maturation and leads to telomere shortening.

Nuclear Pre-snRNA Export Is an Essential Quality Assurance Mechanism for Functional Spliceosomes

“…To challenge the current view that snRNA shuttling evolved only in higher eukaryotes, we systematically explored snRNA shuttling in S. cerevisiae. Due to the fact that Pol II transcripts such as mRNAs and the non-coding telomerase-RNA TLC1 require Mex67-Mtr2 and Xpo1/Crm1 for their nuclear export (Tutucci and Stutz, 2011;Wu et al, 2014), we investigated whether the shuttling of snRNAs would also be dependent on these factors. First, we analyzed potential export defects by fluorescence in situ hybridization (FISH) experiments in mutant forms of Xpo1, Mex67, and its interacting partners Dbp5/Rat8 and Nup159/ Rat7 (Tieg and Krebber, 2013).…”

“…In human cells, CBC binds to PHAX (phosphorylated adaptor RNA export) that in turn recruits the RanGTPase driven exportin CRM1 (chromosome maintenance 1) for nuclear export (Kö hler and Hurt, 2007;Matera and Wang, 2014). In yeast, Pol II transcripts such as mRNAs and the non-coding telomerase-RNA TLC1 use Mex67-Mtr2 (TAP-p15 in human) and Xpo1/Crm1 for their nuclear export (Tutucci and Stutz, 2011;Wu et al, 2014). Interestingly, the current literature suggests that snRNAs do not shuttle in yeast (Olson and Siliciano, 2003;Murphy et al, 2004), although they undergo similar maturation steps as in human cells (Will and L€ uhrmann, 2001;Matera and Wang, 2014;Sloan et al, 2016;Vasianovich and Wellinger, 2017).…”

Nucleocytoplasmic Transport of RNAs and RNA–Protein Complexes

“…The biogenesis pathway of the RNA Pol II transcribed TLC1 RNA somewhat parallels that of pre-snRNAs, but in contrast, nuclear export of TLC1 involves two nuclear transport systems: Crm1 together with the Ran GTPase as well as the Mex67-Mtr2 heterodimer [199,200]. It is not yet know how Crm1 associates with TLC1, but it is likely that an unidentified export adaptor mediates this interaction.…”

“…It is not yet know how Crm1 associates with TLC1, but it is likely that an unidentified export adaptor mediates this interaction. Mutations in Mex67 cause nuclear accumulation of export-competent TLC1 RNAs but it appears that the concerted action of both Crm1 and Mex67-Mtr2 is necessary for efficient biogenesis of telomerase as telomere shortening is only observed in double mutants [200]. Once in the cytoplasm, the export machinery is released and the TLC1 RNA assembles with the reverse transcriptase Est2…”

Efficient Cytoplasmic Delivery of Antisense Probes Assisted by Cyclized‐Peptide‐Mediated Photoinduced Endosomal Escape

“…Telomerase RNA, as a template for nucleotide addition, is essential for the telomerase enzyme . To be fully functional, telomerase RNA has to be shuttled into the cytoplasm to form a complex with other associated proteins (TERT) . If telomerase RNA is blocked, the enzyme is inactivated.…”