M. Savino - Structural and superstructural features of human telomeric chromatin a restriction enzyme assay and of AFM imaging, we demonstrated that nucleosomes shift from telomeric DNA to an adjacent sequence in a temperature and ionic strength dependent manner (Pisano et al., 2007). On the contrary, most nucleosomes formed on an average sequence remain in the starting position. Very recently, we found that TRF1 is able to induce nucleosome mobility (S. P, M. S, S. C., in preparation). This remodelling activity is specific for telomeric nucleosomes since TRF1 has no effect on nucleosomes formed on other sequences. Our findings support the hypothesis that inherent nucleosome mobility depends on DNA sequence, and reveal an unknown property of TRF1 with relevant implications in telomere structure and dynamics. Inhibition of telomerase by targeting human telomere G-quadruplex structures The characterization of the structure of telomeric chromatin represents a relevant research issue, not only as a matter of basic research but also for the implications in cancer research. In most tumors reactivation of telomerase allows to overcome the telomeric checkpoint and to maintain unlimited proliferative activity. Since telomerase is inactive in somatic cells, telomerase represents a specific target for anticancer strategies. The relationship between human telomere G-quadruplex structure and chromatin organization could represent an important way to regulate oncogene transcription. It has been recently shown that PQS (putative quadruplex forming sequences) are present in most proto-oncogenes regulative sequences. In particular, we have recently found a PQS about 100 bp upstream of hTERT, encoding the catalytic subunit 92 of telomerase, corresponding to a major DNaseI hypersensitive site. Targeting this site with polypurinic oligonucleotides gives rise to the formation of a triple helix structure (Rossetti et al., 2007). The stability of this unusual DNA structure was substantially increased by interacting with water soluble perylene derivatives, and represents a promising strategy to inhibit telomerase. We synthesized several polyamine side-chain perylene derivatives and showed that they are able to induce G-quadruplex structures and to inhibit telomerase in a cellfree assay (Franceschin et al., 2008). Our future aim is to test these molecules for their ability to inhibit telomerase in vivo. Selected Publications Pisano S, Marchioni E, Galati A, Mechelli R, Savino M, Cacchione S. Telomeric nucleosomes are intrinsically mobile. J Mol Biol. 2007, 369:1153-62. Rossetti L, D’Isa G, Mauriello C, Varra M, De Santis P, Mayol L, Savino M. A model for triple helix formation on human telomerase reverse transcriptase (hTERT) promoter and stabilization by specific interactions with the water soluble perylene derivative, DAPER. Biophys Chem. 2007, 129:70-81. Franceschin M, Lombardo CM, Pascucci E, D’Ambrosio D, Bianco A, Ortaggi G, Savino M. The number and distances of positive charges of polyamine side chains in a series of perylene diimides significantly influence their ability to induce G-quadruplex structures and inhibit human telomerase. Bioorg Med Chem. 2008, 16:2292-304.
AREA5 Cellular and molecular immunology