Extracellular DNA promotes colorectal tumor cell survival after cytotoxic chemotherapy.

BACKGROUND: Inflammation promotes the growth and survival of malignant cells. Inflammation within the tumor microenvironment is a result of damage-associated molecular patterns released by dead or dying cells that provide survival signals to the surrounding cells. It has been proposed that extracellular DNA can act as a damage-associated molecular pattern given the association between circulating DNA and autoimmune diseases. Herein, we demonstrate a novel role for genomic extracellular DNA binding to the Toll-like receptor (TLR)-9 on tumor cells in response to cytotoxic insult. MATERIALS AND METHODS: The colorectal tumor cell line HCCT116 was used to study the role of DNA in tumor cell response to chemotherapy. Cell viability was assessed using CCK-8 assay. Cell death mechanisms were assessed by YOYO-1 and lactate dehydrogenase staining for necrosis and TUNEL staining for apoptosis. Autophagy was measured by LC3 punctate formation. TLR9-short hairpin RNA was used to knockdown TLR-9 and determine its role in tumor cell response to DNA. RESULTS: DNA is released from necrotic tumor cells after chemotherapy. Survival after cytotoxic insult is enhanced by the presence of extracellular DNA as a result of inhibition of apoptosis and enhanced autophagy. Knockdown of TLR-9 enhanced apoptosis, diminished autophagy, and decreased survival after cytotoxic insult in the presence or absence of extracellular DNA. CONCLUSIONS: DNA in the tumor microenvironment promotes survival through induction of autophagy via TLR-9 signaling. This work has important implications for targeting extracellular DNA, TLR-9, and autophagy during treatment with chemotherapy and enhances our understanding of the role of extracellular DNA in the tumor microenvironment.

Adult pancreatic acinar cells give rise to ducts but not endocrine cells in response to growth factor signaling.

Studies in both humans and rodents have found that insulin(+) cells appear within or near ducts of the adult pancreas, particularly following damage or disease, suggesting that these insulin(+) cells arise de novo from ductal epithelium. We have found that insulin(+) cells are continuous with duct cells in the epithelium that makes up the hyperplastic ducts of both chronic pancreatitis and pancreatic cancer in humans. Therefore, we tested the hypothesis that both hyperplastic ductal cells and their associated insulin(+) cells arise from the same cell of origin. Using a mouse model that develops insulin(+) cell-containing hyperplastic ducts in response to the growth factor TGFalpha, we performed genetic lineage tracing experiments to determine which cells gave rise to both hyperplastic ductal cells and duct-associated insulin(+) cells. We found that hyperplastic ductal cells arose largely from acinar cells that changed their cell fate, or transdifferentiated, into ductal cells. However, insulin(+) cells adjacent to acinar-derived ductal cells arose from pre-existing insulin(+) cells, suggesting that islet endocrine cells can intercalate into hyperplastic ducts as they develop. We conclude that apparent pancreatic plasticity can result both from the ability of acinar cells to change fate and of endocrine cells to reorganize in association with duct structures.