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Circulating nucleic acids damage DNA of healthy cells by integrating into their genomes

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Whether nucleic acids that circulate in blood have any patho-physiological functions in the host have not been explored. We report here that far from being inert molecules, circulating nucleic acids have significant biological activities of their own that are deleterious to healthy cells of the body. Fragmented DNA and chromatin (DNAfs and Cfs) isolated from blood of cancer patients and healthy volunteers are readily taken up by a variety of cells in culture to be localized in their nuclei within a few minutes. The intra-nuclear DNAfs and Cfs associate themselves with host cell chromosomes to evoke a cellular DNA-damage-repair-response (DDR) followed by their incorporation into the host cell genomes. Whole genome sequencing detected the presence of tens of thousands of human sequence reads in the recipient mouse cells. Genomic incorporation of DNAfs and Cfs leads to dsDNA breaks and activation of apoptotic pathways in the treated cells. When injected intravenously into Balb/C mice, DNAfs and Cfs undergo genomic integration into cells of their vital organs resulting in activation of DDR and apoptotic proteins in the recipient cells. Cfs have significantly greater activity than DNAfs with respect to all parameters examined, while both DNAfs and Cfs isolated from cancer patients are more active than those from normal volunteers. All the above pathological actions of DNAfs and Cfs described above can be abrogated by concurrent treatment with DNase I and/or anti-histone antibody complexed nanoparticles both in vitro and in vivo. Taken together, our results that circulating DNAfs and Cfs are physiological, continuously arising, endogenous DNA damaging agents with implications to ageing and a multitude of human pathologies including initiation of cancer.

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We sincerely thank Dr LC Padhy for most generously offering his time during numerous scientific discussions, for his invaluable suggestions and for his critical inputs into the manuscript. We thank Dr AN Ghosh for taking the EM images. We acknowledge the contribution made by the many lab members who have contributed to this project over the years. Special thanks are due to Nagnath Swamy, Shazia Mansoor, Nabila Akhtar, Mansoor Ali, Rashmi Malvee, Arpit Bhargava, Preetam Bala, Mihir Shetty, Ajay Choudhary and Mihir Parmar. This study was supported by the Department of Atomic Energy, Govt. of India, through its grant CTCTMC to Tata Memorial Centre awarded to IM. AD is supported by an Intermediate fellowship from the Wellcome Trust/DBT India Alliance (IA/I/11/2500278), by a grant from Department of Biotechnology, Govt. of India (BT/PR2372/AGR/36/696/2011), and intramural grants (Seed-In-Air 2897, TMH Plan Project 2712 and IRB 92). PU is supported by Senior Research Fellowship from Council of Scientific & Industrial Research, Govt. of India.

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Correspondence to Indraneel Mittra.

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Corresponding editor: Stuart A Newman

[Mittra I, Khare NK, Raghuram GV, Chaubal R, Khambatti F, Gupta D, Gaikwad A, Prasannan P, Singh A, Iyer A, Singh A, Upadhyay P, Nair NK, Mishra PK and Dutt A 2015 Circulating nucleic acids damage DNA of healthy cells by integrating into their genomes. J. Biosci. 40 91–111] DOI 10.1007/s12038-015-9508-6

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Mittra, I., Khare, N.K., Raghuram, G.V. et al. Circulating nucleic acids damage DNA of healthy cells by integrating into their genomes. J Biosci 40, 91–111 (2015).

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