The Role of C-X-C Motif Chemokine Ligand 10 (CXCL10) in Osteosarcoma Metastasis
Introduction
Osteosarcoma is the most common malignant bone tumor in children. Despite the use of chemotherapy and surgery, the survival of patients with metastasis is still dismal. We have previously reported that circulating CXCL10 is associated with a poor prognosis and metastasis in osteosarcoma. CXCL10 mediates cellular phenotypes via autocrine and paracrine signaling. Nonetheless, the functional effect and the mechanism of circulating CXCL10 on osteosarcoma metastasis are poorly understood.
Methods
In this study, we performed in vitro transwell migration assays and Western blotting on osteosarcoma cell lines to examine the effect of CXCL10 on tumor cell migration and AKT signaling, respectively. Next, we tested whether increasing the level of circulating CXCL10 can promote osteosarcoma metastasis. To test that, we injected luciferase-labeled 143B osteosarcoma cells into the tibia of NOD/SCID mice to generate an orthotopic xenograft mouse model. When the tumor was detectable by bioluminescence, we administrated CXCL10 protein or saline intravenously via the tail vein every day for two weeks. The development of pulmonary metastasis was monitored by bioluminescence. The mice were sacrificed at the endpoint when bioluminescence was detected in the lungs. The mouse lungs were then resected and examined histologically for the presence of metastatic nodules. The number of mice in the experimental and control groups that developed lung metastases were compared.
Results
Our results showed that the exogenous addition of CXCL10 promoted the tumor cell migration of three osteosarcoma cell lines in vitro. We also demonstrated that AKT phosphorylation was upregulated in the osteosarcoma cell lines incubated with CXCL10. These results suggest that CXCL10 can directly promote AKT activation and osteosarcoma cell motility, probably through autocrine signaling. However, the result of the xenograft mouse study showed that no significant difference in the number of mice developing pulmonary metastases was observed between the groups administrated with CXCL10 and saline. To investigate the influence of the cell line background, we analyzed another osteosarcoma cell line, MG63.3. No significant difference in metastasis development was observed.
Conclusion
In summary, our results indicate that CXCL10 can directly influence osteosarcoma cell migration and AKT signaling, whereas an elevated level of circulating CXCL10 does not affect the development of pulmonary metastasis. Our current model is that the metastatic effect of CXCL10 on osteosarcoma is mainly manifested by increased autocrine signaling, which may result in a higher circulating level of the chemokine.