Characterization of the telomeric repeat binding factor 2 (TRF2) in the UV-induced DNA damage response and telomere maintenance

Abstract

TRF2 is an essential telomeric protein involved in preventing the telomere ends from being recognized as DNA breaks. I have shown that TRF2 does not appear to play a major role in the UV -induced DNA damage response in IMR90, Cockayne syndrome or XPC deficient cells. TRF2 binds telomeric DNA via its Myb domain and also contains an N-terminal basic domain. Expression of TRF2MMM causes telomere fusions, whereas TRF2^(ΔB) causes rapid deletion of telomeric DNA, as both phenotypes result in senescence. These phenotypes are dependant upon recombination events. Thus, the basic domain of TRF2 may be essential to suppress recombination events at telomeres. However, it is not fully understood what amino acid residues in the basic domain of TRF2 are indispensable to maintain its function. By creating mutations in the arginine residues in the basic domain of TRF2, I have shown that the positive charge of the basic domain alone is not sufficient to maintain its protective function. By expressing these TRF2 mutants in the presence or absence of the Myb domain in HT1080 and BJ/hTERT cells, I have been able to recapitulate the TRF2^(ΔB) and TRF2^(ΔBΔM) decreased proliferation and senescence phenotypes. Furthermore, by analyzing anaphase and metaphase chromosomes and performing Southern blotting, I have shed light on the molecular mechanisms responsible for the deleterious phenotypes observed in the TRF2 mutants. Amino acid changes from arginines to lysines introduced into the basic domain of TRF2 results in a significant increase in telomere doublets. However, when these TRF2 mutants are expressed in the absence of the Myb domain, a significant increase in telomere fusions events occur. Collectively, my results indicate that more than one arginine residue in the basic domain is essential to maintain the protective function of TRF2, as these arginine residues may act as substrates for protein arginine methyltransferases.