Potential Anticancer Activity Via Inhibition Of Telomerase Binding Investigation Of Stabilization Factors For G Quadruplex Structures

Author : Johanna Mancini
Publisher :
ISBN 13 :
Total Pages : pages
Book Rating : 4.:/5 (964 download)

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Download or read book Characterizing and Targeting Unique Features of Telomeres and Telomere Maintenance written by Johanna Mancini and published by . This book was released on 2016 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: "Telomere maintenance, achieved by the binding of protective shelterin capping proteins and by either telomerase or homologous recombination-based alternative lengthening of telomere (ALT) mechanisms, is critical for cell proliferation and survival. Loss of telomeric integrity or extensive telomere shortening activates DNA damage checkpoints, leading to the initiation of genomic instability, cell senescence, or death. Although telomerase is an attractive target for anti-cancer therapy, the lag associated with telomere shortening poses a challenge. An alternative approach is to modify telomere interactions with binding proteins (telomere uncapping) or to interfere with telomerase access. This can be accomplished through the use of G-quadruplex ligands that stabilize structures from single-stranded G-rich 3′-telomere end (G-quadruplex) folding, which cannot be elongated by telomerase and which can mediate rapid anti-proliferative effects by telomere uncapping. Inhibition of telomerase may also cause the onset of ALT. Despite its potential to serve as a target for anti-cancer therapy, the ALT pathway remains poorly characterized. The ALT pathway maintains telomeres using homologous recombination, which also occurs throughout the genome in order to repair sites of DNA damage due to or resulting in replication fork stalling. Although ALT is often associated with high levels of small ubiquitin-related modifier (SUMO), decreased levels of SUMO1 were observed in a telomerase-positive human breast cancer cell line harboring an ALT phenotype. In yeast, sumoylation of the DNA replication/repair machinery has been shown to recruit an anti-recombinogenic helicase. Recent identification of the human orthologue, Proliferating Cell Nuclear Antigen (PCNA)-Interacting Protein (PARI), led us to investigate the role of sumoylation in the regulation of ALT and to suggest a role for PARI in regulating telomeric recombination in ALT cells.Our results confirm that G-quadruplex ligands PIN, PIP, PII, PIQ, SIP, and CLIP can inhibit telomerase activity in vitro. Treatment with PIP is able to significantly reduce proliferation of A549 lung cancer cells and to cause a significant decrease in the average telomere length of these cells. Although the growth of normal primary cells with a limited capacity for replication was also affected, their telomere length of was not significantly decreased. While treatment with PIP failed to induce apoptosis and DNA damage localized at the telomere; positive staining for [beta]-galactosidase, in telomerase positive A549 and Huh7 cells, confirmed the onset of cellular senescence. Interestingly, expression of the inactive -[beta] splice variant of hTERT was increased after short-term treatment with PIP. These results suggest that the observed anti-proliferative effects are unlikely due to telomere uncapping but rather due to the inhibition of telomerase activity, leading to cellular senescence. Preliminary results investigating the role of PARI at the telomere suggest it is capable of repressing homologous recombination. Overexpression of PARI inhibited homologous recombination at telomeres, observed by a decrease in C-circle expression, the most robust method of measuring ALT. Moreover, PARI containing mutations in critical SUMO- ([DELTA]SIM) and PCNA- ([DELTA]PIP) interacting sites were less effective at inhibiting homologous recombination activity; thus supporting the characterization of PARI and its potential role in telomeric recombination. These studies validate the development of novel and specific therapeutic ligands that target G-quadruplex structures at the telomere. Moreover, they identify potential novel targets of the ALT pathway, providing evidence that PARI can inhibit recombination at the telomere; thus improving our understanding of the mechanisms regulating telomere maintenance." --