Introduction

In response to detection of cytosolic double-stranded DNA STING signaling induces type I interferon and chemokine expression, and promotes T lymphocyte recruitment. STING is therefore critical for inducing an immune response to cells experiencing DNA damage. The objectives of this study were to determine the integrity of STING signaling in canine and human osteosarcoma (OSA) cell lines, and to correlate STING expression with cytokine/chemokine expression after radiation.

Methods

We utilized four human OSA cell lines (U2OS, MG63, SAOS-2, SAOS-2_LM6), three canine OSA cell lines (D17, Khepri, Brutus), and human and canine osteoblasts. STING expression was quantified by Western blot and mass spectrometry, and pathway integrity was tested by exposing cells to 10 μg/ml of 2’3’-cGAMP and measuring downstream transcripts by RT-qPCR, and chemokine excretion by ELISA. Cells were exposed to 0, 5, or 10 Gy and expression of downstream cytokine/chemokines was quantified by RT-qPCR at multiple timepoints.

Results

STING is frequently downregulated in human and canine OSA cell lines. STING-deficient cell lines display dampened expression of CCL5 and CXCL10 after treatment with the STING agonist 2’3’-cGAMP. CCL5 upregulation in irradiated cells is consistently dampened in the STING-deficient SAOS-2 cell line, while robust increases are seen in the STING-proficient SAOS-2_LM6 cell line at day 3 and 6. Additional data collection is in progress.

Conclusion

The integrity of STING signaling in OSA cells may affect the degree of immune modulation induced by radiation. Further studies are necessary to determine if STING signaling in OSA cells influences the anti-tumor immune response within the complex tumor microenvironment.

Funding Information

Research reported in this abstract was supported by the LSU School of Veterinary Medicine Competitive Research Program.