Cell cycle-dependent resolution of DNA double-strand breaks.

// Susanna Ambrosio 1 , Giacomo Di Palo 2 , Giuliana Napolitano 1 , Stefano Amente 2 , Gaetano Ivan Dellino 3, 4 , Mario Faretta 3 , Pier Giuseppe Pelicci 3, 4 , Luigi Lania 2 , Barbara Majello 1 1 Department of Biology, University of Naples ‘Federico II’, Naples, Italy 2 Department of Molecular Medicine and Medical Biotechnologies, University of Naples ‘Federico II’, Naples, Italy 3 Department of Experimental Oncology, European Institute of Oncology, Milan, Italy 4 Department of Oncology and Haemato-oncology, University of Milan, Italy Correspondence to: Luigi Lania, e-mail: lania@unina.it Barbara Majello, e-mail: majello@unina.it Keywords: cell-cycle, DSB repair, site-specific DSBs, AsiSI restriction enzyme Received: November 05, 2015      Accepted: November 27, 2015      Published: December 17, 2015 ABSTRACT DNA double strand breaks (DSBs) elicit prompt activation of DNA damage response (DDR), which arrests cell-cycle either in G 1 /S or G 2 /M in order to avoid entering S and M phase with damaged DNAs. Since mammalian tissues contain both proliferating and quiescent cells, there might be fundamental difference in DDR between proliferating and quiescent cells (or G 0 -arrested). To investigate these differences, we studied recruitment of DSB repair factors and resolution of DNA lesions induced at site-specific DSBs in asynchronously proliferating, G 0 -, or G 1 -arrested cells. Strikingly, DSBs occurring in G 0 quiescent cells are not repaired and maintain a sustained activation of the p53-pathway. Conversely, re-entry into cell cycle of damaged G 0 -arrested cells, occurs with a delayed clearance of DNA repair factors initially recruited to DSBs, indicating an inefficient repair when compared to DSBs induced in asynchronously proliferating or G 1 -synchronized cells. Moreover, we found that initial recognition of DSBs and assembly of DSB factors is largely similar in asynchronously proliferating, G 0 -, or G 1 -synchronized cells. Our study thereby demonstrates that repair and resolution of DSBs is strongly dependent on the cell-cycle state.