The regulatory functions of circular RNAs in osteosarcoma.

Osteosarcoma (OS) is known as a malignant bone tumor affecting mainly children and younger adults. Despite all the improvements in the treatment of OS, the overall survival among patients remained mostly unsatisfied. It involves different mechanisms and signaling pathways. Some recent studies confirmed that circular RNAs (circRNAs) have a revelatory role in controlling OS cell proliferation, invasion, and metastasis. CircRNAs consist of a covalently closed-loop structure with neither 5' nor 3' poly adenylated tail, lacking protein-encoding ability formed by back-splicing mechanisms. They mainly act as microRNA (miRNA) sponges and modulate the downstream biological processes. Up/down regulation of some circRNAs demonstrated to serve as the oncogenic factor in some tumor tissues such as OS. In this article, we review the regulatory functions of circRNAs resulting in OS cell progression or restraint and the potential for being used in vitro or in vivo as diagnostic or therapeutic biomarkers.