Ribosomal DNA as DAMPs Signal for MCF7 Cancer Cells.

Area of Science:

• Molecular Biology
• Cancer Research
• Immunology

Background:

• Cell free ribosomal DNA (cf-rDNA) is found in cell free DNA (cfDNA) in non-cancer diseases and acts as a damage-associated molecular pattern (DAMP).
• The role and impact of cf-rDNA in breast cancer, including its effect on cancer cells and specific DNA sensors, remain largely unexplored.

Purpose of the Study:

• To investigate the changes in cf-rDNA content in breast cancer patients.
• To determine the response of MCF7 breast cancer cells to cf-rDNA.
• To identify the DNA sensors (TLR9 or AIM2) activated by cf-rDNA in MCF7 cells.

Main Methods:

• Isolation of cell free DNA (cfDNA) and genomic DNA (gDNA) from breast cancer patients and healthy controls.
• Quantitative hybridization to determine rDNA content.
• In vitro studies using MCF7 cells with model DNA constructs (GC-DNAs) to assess ROS generation, DNA damage, cell cycle, gene expression (TLR9, AIM2, NF-kB, STAT3, apoptosis-related genes), using RT-qPCR, fluorescent microscopy, immunoassay, flow cytometry, and siRNA.

Main Results:

• Significantly higher cf-rDNA/g-rDNA ratio (R) observed in breast cancer patients compared to controls (median 3.4 vs. 0.8, p < 10^-8).
• Exposure to GC-DNAs in MCF7 cells induced reactive oxygen species (ROS) burst, DNA damage, and activated NF-kB and STAT3 signaling.
• cf-rDNA promoted cell survival by decreasing apoptosis and increasing genomic instability (G2/M arrest, micronuclei), activating TLR9-MyD88-NF-kB signaling and suppressing AIM2 expression.

Conclusions:

• Ribosomal DNA accumulates in the cfDNA of breast cancer patients.
• Cell free rDNA triggers DNA damage response and enhances cancer cell survival, particularly in cells with genomic instability.
• Cell free rDNA activates the TLR9-MyD88-NF-kB pathway, leading to the significant repression of AIM2 expression in breast cancer cells.