Background: Osteosarcoma (OS) is a highly prevalent bone malignancy with poor clinical outcomes. Expression of the circular RNA, hsa_circ_0078767 (circFAM120B) is elevated in OS, however, its mechanisms in OS are unclear.

Methods: CircFAM120B levels were detected in OS tissue and cell lines. Silenced circFAM120B experiments were performed to assess its effects on OS in vitro cancer phenotypes and in vivo tumor growth. Then, bioinformatics analyses were used to predict circFAM120B target microRNAs (miRNAs) and associated genes.

Results: CircFAM120B and the transcription factor, PTBP1 were elevated in OS tissue and cell lines, while miR-1205 was poorly expressed. Silenced circFAM120B significantly suppressed in vitro OS cell proliferation and invasion, and inhibited in vivo tumor growth. CircFAM120B also appeared to function as an miR-1205 sponge, as miR-1205 bound to PTBP1. Interestingly, overexpressed PTBP1 (or miR-1205 inhibition) reversed the inhibitory effects mediated by circFAM120B downregulation in OS cells.

Conclusion: We hypothesize circFAM120B functions as a miR-1205 sponge to elevate PTBP1 levels, enhancing OS progression and associated malignant phenotypes. Thus, circFAM120B may function as a crucial mediator during OS progression.