While the majority of cancer cells achieve unlimited proliferative potential through over-expression and activation of telomerase, a subset of cancer cells do so through the Alternative Lengthening of Telomeres (ALT) pathway. Telomeric recombination is believed to be the main mechanism in the ALT phenotype. Unlike telomerase-positive cells, cancer cells utilising ALT pathways have distinct characteristics such as heterogenous telomere length and ALT-associated PML nuclear bodies (APBs), which are therefore markers of the ALT phenotype. APBs differ from PML nuclear bodies (NB) in that telomeric DNA, telomeres-associated proteins such as telomeric-repeat binding factors (TRF) 1 and 2, and DNA repair and recombination proteins co-localise to APBs. As such, APBs have been suggested to be sites whereby proteins involved in the ALT pathway are focused and modified, and as sites for the repair of telomeric DNA and telomeric recombination. A major constituent of APBs is the Promyelocytic Leukemia protein (PML), which has to be modifiable by the Small Ubiquitin-like Modifier (SUMO) protein. The SUMOylation of PML is essential for the formation of PML NBs. In our study, we sought to disrupt the APBs through the over-expression of a coiled-coil deletion mutant of PML and to determine the long-term effects of such over-expression on telomere length and cell viability of ALT cells. Here, we report that while the over-expressed wild-type PML is SUMOylated, the coiled-coil deletion PML mutant cannot be SUMOylated in the ALT cell-lines used, namely in jejunal JFCF-6/T.1R and osteosarcoma U2OS. In addition, over-expressed wild-type PML leads to the formation of nuclear bodies that are bigger in size compared to endogenous nuclear bodies and it co-localises with TRF2 to form APBs. However, the coiled-coil deletion PML mutant does not form any distinct nuclear bodies that co-localises with TRF2. As there is a strong correlation between the presence of APBs and the occurrence of the ALT mechanism, we postulate that by interfering with and/or manipulating the APBs in ALT cells, we could interfere with the ALT pathway of telomere maintenance.
Citation Information: In: Proc Am Assoc Cancer Res; 2009 Apr 18-22; Denver, CO. Philadelphia (PA): AACR; 2009. Abstract nr 3483.
100th AACR Annual Meeting-- Apr 18-22, 2009; Denver, CO