Autophagy acts as a safeguard mechanism against G-quadruplex ligand-mediated DNA damage.

Nicola Ivan Orlotti, Graziella Cimino-Reale, Erika Borghini, Marzia Pennati, Claudia Sissi, Federica Perrone, Manlio Palumbo, Maria Grazia Daidone, Marco Folini, Nadia Zaffaroni

Department of Experimental Oncology and Molecular Medicine, Fondazione IRCCS Istituto Nazionale dei Tumori, Milan, Italy.

Autophagy 2012 Aug

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G-quadruplex ligands have attracted considerable interest as novel anticancer therapeutics due to their capability to interfere with guanosine-rich DNA/RNA sequences, such as telomeres. Elucidation of the structures of telomeric G-quadruplexes has led, in the past few years, to the rational development of effective G-quadruplex-stabilizing small molecules. In the present study, we showed that short-term exposure of melanoma cells to Ant1,5--an anthracene-based ligand able to stabilize telomeric G-quadruplexes--impaired cell growth without inducing cell senescence or apoptosis. Conversely, drug-treated cells were characterized by the occurrence of typical biochemical and morphological features associated with autophagy, such as an increase in the lipidated form of the autophagic marker LC3B and the accumulation of autophagosomes. Such drug-induced autophagy occurred as a consequence of DNA damage induction, at least in part dependent on drug-mediated telomere uncapping, through a pathway converging on the cyclin-dependent kinase inhibitor 1A (CDKN1A/p21). Indeed, melanoma cells depleted for CDKN1A did not show evidence of autophagic markers upon exposure to Ant1,5. The inhibition of autophagy by a pharmacologic inhibitor or through RNAi-mediated depletion of the ATG5 gene enhanced the cytotoxic activity of Ant1,5, as revealed by the marked increase in drug-induced apoptosis. Our data outline a molecular scenario in which G-quadruplex ligand-induced telomeric dysfunctions and DNA damage are translated into an autophagic response and provide the first evidence of autophagy as a safeguard mechanism activated by melanoma cells to counteract G-quadruplex ligand-mediated cellular stress.

Citation

Nicola Ivan Orlotti, Graziella Cimino-Reale, Erika Borghini, Marzia Pennati, Claudia Sissi, Federica Perrone, Manlio Palumbo, Maria Grazia Daidone, Marco Folini, Nadia Zaffaroni. Autophagy acts as a safeguard mechanism against G-quadruplex ligand-mediated DNA damage. Autophagy. 2012 Aug;8(8):1185-96