Extracellular DNA in Pancreatic Cancer Promotes Cell Invasion and Metastasis

Abstract

Aggressive metastasis is the chief cause of the high morbidity and mortality associated with pancreatic cancer, yet the basis for its aggressive behavior remains elusive. Extracellular DNA (exDNA) is a recently discovered component of inflammatory tissue states. Here we report that exDNA is present on the surface of pancreatic cancer cells where it is critical for driving metastatic behavior. ExDNA was abundant on the surface and vicinity of cultured pancreatic cancer cells, but absent from normal pancreas cells. Strikingly, treatment of cancer cell cultures with DNase I to degrade DNA non-specifically reduced metastatic characters associated with matrix attachment, migration and invasion. We further assessed the role of exDNA in pancreatic cancer metastasis in vivo using an orthotopic xenograft model established by implantation of pancreatic cancer cells expressing firefly luciferase. Non-invasive bioluminescent imaging confirmed that DNase I treatment was sufficient to suppress tumor metastasis. Mechanistic investigations suggested the existence of a positive feedback loop in which exDNA promotes expression of the inflammatory chemokine CXCL8 which leads to higher production of exDNA by pancreatic cancer cells, with a significant reduction in CXCL8 levels achieved by DNase I treatment. Taken together, our results strongly suggest that exDNA contributes to the highly invasive and metastatic character of pancreatic cancer.

Extracellular DNA: A Bridge to Cancer

“…1D; ref. 40). DNase I treatment of pancreatic cancer cells resulted in reduced migration, adhesion, and invasion, as well as production of the inflammatory chemokine CXCL8 ( Table 1).…”

“…This concept provides a new basis for interpreting long-standing observations that increased exDNA (also called circulating free DNA or cfDNA), and reduced DNase levels in human blood occur in correlation with cancer development and progression (25)(26)(27)(28)(29)(30)(31)(32)(33). Studies by independent laboratories around the world, moreover, repeatedly have documented that DNase 1 added to diverse cancer cells inhibits their metastatic potential (30,(34)(35)(36)(37)(38)(39)(40)(41).…”

“…Meanwhile, the values for exDNA in blood have been proposed to comprise important clinical information regardless of whether future studies reveal that the exDNA includes tumor sequences and/or is derived of extracellular trap DNA (33). Either model could account for observations that the exDNA of cancer patients can facilitate oncogenic transformation, and that DNase I treatment of cancer cells or the supernatants of cancer patients removes the capacity to metastasize (30,36,40,41). These data highlight potential avenues to control cancer by establishing protocols to define and maintain healthy exDNA and DNase I levels (14).…”

Cell-Free eccDNAs: A New Type of Nucleic Acid Component for Liquid Biopsy?

“…Recently, exDNAs were proved to play important roles for cancer cell invasion and metastasis. Treatment of cells using DNase I significantly reduced the invasion and metastatic capability of tumor cells (55). Circulating exDNA is basically a component of circulating cfDNA.…”

Signals Controlling Extracellular Trap Formation in Plant and Animal Immune Responses

“…Rapid progress in describing the role of exDNA-based trapping in defense by neutrophils, eosinophils, and other cell types and its interaction with bacterial, fungal, viral, and protozoan pathogens is underway [5][6][7][8]. ExDNA also has been implicated in autoimmune diseases including lupus, rheumatoid arthritis, and cancer [9][10][11]. It is now clear that exDNA plays a critical role in cellular defense in animals, and that microbial expression of extracellular DNase (exDNase) is a key virulence factor in pathogenesis [12][13][14][15].…”