The non-vesicle extracellular DNA induces cell transformation associated with horizontal DNA transfer

Abstract

Abstract Extracellular DNA (exDNA) is a source for liquid biopsy used for cancer diagnosis, therapy selection, and disease monitoring due to its non-invasive nature and ease of extraction. However, exDNA also participates in cancer development and progression by horizontal transfer. In humans, exDNA circulates complexed with extracellular vesicles (EV) and macromolecular complexes such as nucleosomes, lipids, and serum proteins. The present study aimed to demonstrate whether exDNA not associated with EV induces cell transformation and tumorigenesis. For that purpose, the supernatant of the SW480 human colon cancer cell line was processed by ultracentrifugation to obtain a soluble fraction (SF) and a fraction associated with EV (EVF). Primary murine embryonic fibroblast cells (NIH3T3) underwent passive transfection with these fractions, and cell proliferation, cell cycle, apoptosis, cell transformation, and tumorigenic assays were performed. Next, exDNA was analyzed by electronic microscopy, and horizontal transfer was assessed by human mutant KRAS in recipient cells via PCR and recipient cell internalization via fluorescence microscopy. The results showed that the SF but not the EVF of exDNA induced proliferative and antiapoptotic effects, cell transformation, and tumorigenesis in nude mice, which were reduced by digestion with DNAse I and proteinase K. These effects were associated with horizontal DNA transfer and exDNA internalization into recipient cells. The present results suggest pro-tumorigenic effects of exDNA in the SF that can be offset by enzyme treatment. Further exploration of the horizontal tumor progression phenomenon mediated by exDNA is needed to determine whether its manipulation may play a role in cancer therapy.