Cell-free ribosomal DNA can induce an adaptive response in the cancer cells - 11th International Symposium on Circulating Nucleic Acids in Plasma and Serum (CNAPS)

Ekaterina Kozhina ¹ Elena Malinovskaya ¹ Nadezhda Mordkovich ² Natalya Okorokova ² Vladimir Veiko ² Elizaveta Ershova ^1,3 Marina Konkova ¹ Ekaterina Savinova ¹ Nataly Veiko ¹ Svetlana Kostyuk ^1,3

¹Laboratory of molecular biology, Research Centre for Medical Genetics (RCMG), Moscow, Russia
²Laboratory of Molecular Engineering, Bach Institute of Biochemistry, Biotechnology Research Center, Moscow, Russia
³Laboratory of Health and Quality of Life of Students, I.M. Sechenov First Moscow State Medical University, Moscow, Russia

Background. Anticancer therapy stimulates the death of a large number of cells. DNA of the dead cells replenishes the pool of cell-free DNA (cfDNA). Ribosomal DNA (rDNA) accumulates in cfDNA of the treated breast cancer patients. RDNA is prone to oxidation. Oxidized DNA induces adaptive response (AR) in the cancer cells. Therefore, we hypothesized that rDNA can stimulate AR in the cancer cells.

Methods. Two types of cf-rDNA fragments were added to the medium of human adenocarcinoma cells MCF7: (1) the plasmid pBR322-rDNA (rDNA inset 5836 bp long) and pBR322 (control); (2) cfDNAs from the treated breast cancer patients and healthy donors (control) with the known content of rDNA. ROS generation rate, rDNA oxidation, expression of NOX4 and RNA for genes affecting the cancer cell viability were evaluated. Applied methods were qPCR, fluorescent microscopy, immunoassay, flow cytometry.

Results. At the site of cf-rDNA contact with the cell, NOX4 is expressed. All the cf-rDNA caused the burst of ROS in the first minutes of exposure to the cells. ROS oxidize cf-rDNA strongly than control cfDNA. Oxidized cf-rDNA penetrates into the cell and induce ROS synthesis in mitochondria. ROS damage nuclear DNA by inducing DNA breaks. DNA damage stimulates the DNA damage response (DDR). In the presence of cf-rDNA the number of cells with an instable genome (micronuclei and G2/M– arrest) increase. Expression of anti-apoptotic genes is elevated and expression of pro-apoptotic genes is lowered. The cells AR for rDNA is realized through activation of NF-kB- signaling and DDR-signaling.

Conclusion: Cf-rDNA stimulates cancer cells survival, including the cells with an instable genome. Lock cf-rDNA activity can increase the effectiveness of anticancer therapy.

The study was supported by the Russian Academy of Science Presidium (№. 0517-2018-0003).