Telomeres are important in maintaining the integrity of the chromosomes. A series of shelterin proteins (TRF1, TRF2, RAP1, POT1a and b, TIPP1 and TIN2), are involved in the maintenance and synthesis of telomeres. In chronic lymphocytic leukemia (CLL), the telomeres are shorter than in normal B cells, with very short telomeres being associated with poor survival. The mechanism for this telomere shortening has been evaluated in the present study. We demonstrated in 150 CLL patients using a Q-RT-PCR assay that the median telomere length was similar in mutated IgVH (Mu-IgVH) cases as in normal B cells, but was significantly shorter in unmutated (Un-IgVH) cases. However, there was considerable variation and overlap in telomere length between the groups. In addition, telomere length was found to shorten in both IgVH mutated and unmutated groups when patients were sequentially followed over years indicating that telomere shortening was an ongoing process. When lymphocytes were stimulated and the telomeres evaluated in metaphase by Q-FISH, telomere length shortening affected all chromosomes equally. To determine if telomere shortening in CLL cells was related to increased free radical formation, we measured plasma lipid peroxidation level (Lipid Hydroperoxide (LPO) assay, Cayman) and DNA breaks (gamma H2AX). As compared to normal B cells, there was increased lipid peroxidation and DNA breaks in both mutated and unmutated CLL cells. When cells were treated with N-acetyl-L-cysteine to scavenge free radicals, there was a decrease in DNA breakage. To assess, whether these changes were associated with alterations of the shelterin complex, protein levels of the shelterins were measured. TRF1 and TRF2 protein levels were increased in all patients compared to normal B cells. TRF2 was also increased in the cytoplasm of CLL cells. Following drug induced apoptosis in CLL cells TRF2 levels decreased but not TRF1 levels. In summary, these studies suggest that the short telomeres in CLL may be related to increased oxidative stress in these cells. TRF1 and TRF2 levels were increased in CLL cells regardless of telomere length suggesting that abnormalities in these proteins may also be involved in telomere shortening. Ongoing studies are evaluating the mechanisms responsible for the shelterin changes in CLL cells and whether altering the levels of these proteins can influence cell death.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 4983. doi:1538-7445.AM2012-4983

©2012 American Association for Cancer Research
2012