Telomere-binding Protein TRF2 Binds to and Stimulates the Werner and Bloom Syndrome Helicases

Abstract

Werner syndrome is a human premature aging disorder displaying cellular defects associated with telomere maintenance including genomic instability, premature senescence, and accelerated telomere erosion. The yeast homologue of the Werner protein (WRN), Sgs1, is required for recombination-mediated lengthening of telomeres in telomerase-deficient cells. In human cells, we report that WRN co-localizes and physically interacts with the critical telomere maintenance protein TRF2. This interaction is mediated by the RecQ conserved Cterminal region of WRN. In vitro, TRF2 demonstrates high affinity for WRN and for another RecQ family member, the Bloom syndrome protein (BLM). TRF2 interaction with either WRN or BLM results in a notable stimulation of their helicase activities. Furthermore, the WRN and BLM helicases, partnered with replication protein A, actively unwind long telomeric duplex regions that are pre-bound by TRF2. These results suggest that TRF2 functions with WRN, and possibly BLM, in a common pathway at telomeric ends.

Functional Interaction between Poly(ADP-Ribose) Polymerase 2 (PARP-2) and TRF2: PARP Activity Negatively Regulates TRF2

“…Although we could not detect PARP-2 colocalized with TRF2 in telomerase-positive cell lines, we cannot exclude its presence at telomeres, which could be masked by the strong homogeneous PARP-2 nuclear signal. Key players in DNA repair and recombination are localized to APB, including the RAD50/MRE11/NBS1 complex, RAD52, RPA, and the RecQ family helicases BLM and WRN (32,40,61,65). It was originally proposed that the function of APB is to repair telomeric DNA that is recognized by the cell as it is being damaged.…”

The role of DNA exonucleases in protecting genome stability and their impact on ageing

“…Indeed, a K577M point mutation within the helicase domain has a dominant negative effect on any subsequent exonuclease activity and prevents lagging strand Okazaki fragment processing at the telomere (Crabbe et al 2004). (Note that WRN also binds to telomere proteins POT1 and TRF2 (Opresko et al 2002(Opresko et al , 2005). Interestingly, WRN also interacts physically with and stimulates EXO1 (Aggarwal et al 2010;Sharma et al 2003), a nuclease that is implicated both in Okazaki fragment processing and in telomere processing.…”

Cancer and aging: the importance of telomeres in genome maintenance

“…In addition, TRF2 interacts with several proteins that participate in DNA damage sensing or repair, including the RAD50-MRE11-NBS1 (RMN) complex [79], which is crucial for homologous recombinational repair (HR) and may also participate in NHEJ [80]. TRF2 also interacts with the DNA damage sensing protein ATM, and is thought to inhibit ATM activity specifically at telomeres [81], and WRN [82], the protein that is defective in the human premature aging and cancer-prone disorder Werner syndrome [83,84]. WRN encodes a DNA helicase and exonuclease [85,86] that appears to participate in both the NHEJ and HR DNA repair pathways [87][88][89][90][91][92][93][94].…”