Osteosarcoma is the most common primary malignant bone tumor in adolescents. While chemotherapy combined with surgery can improve the prognosis of some patients, chemo-resistance is still a huge obstacle in osteosarcoma treatment. Accumulating evidence demonstrates that circular RNAs (circRNAs) are involved in cancer progression and metastasis, but their specific role in osteosarcoma remains mostly undescribed. In this study, we performed circRNA deep sequencing and identified 88 distinct circRNAs from a human osteosarcoma cell lines group (143B, HOS, SJSA, and U2OS) and the human osteoblast hFOB 1.19 (control). We found that circCAMSAP1, also named hsa_circ_0004338, is significantly upregulated in human osteosarcoma tissues and cell lines, and it is positively correlated with osteosarcoma development. Silencing of circCAMSAP1 effectively suppresses osteosarcoma cell growth, apoptosis, migration, and invasion. Furthermore, we validated that circCAMSAP1 functions in osteosarcoma tumorigenesis through a circCAMSAP1/miR-145-5p/friend leukemia virus integration 1 (FLI1) pathway. FLI1 promotes osteosarcoma tumorigenesis and miR-145-5p suppresses FLI translation. circCAMSAP1 directly sequesters miR-145-5p in the cytoplasm and inhibits its activity to suppress osteosarcoma tumorigenesis. Moreover, the regulatory role of circCAMSAP1 upregulation was examined and validated in rats. In summary, our findings provide evidence that circCAMSAP1 act as a “microRNA sponge” and suggest a new therapeutic target of human osteosarcoma.

Papillary thyroid cancer (PTC) has a continuously increasing incidence and imposes a heavy medical burden to individuals and society due to its high proportion of lymph node metastasis and recurrence in recent years. Circular RNAs, a class of noncoding RNAs, participate in the progression of many cancers, but the role of circRNAs in PTC is still rarely reported. In this study, circRNA deep sequencing was performed to identify differentially expressed circRNAs in PTC. CircRUNX1 was selected for its high expression in PTC, and circRUNX1 silencing was directly associated with the week potential for migration, invasion and proliferation of PTC in vivo and in vitro. Fluorescence in situ hybridization (FISH) was further used to confirm the cytoplasmic localization of circRUNX1, indicating the possible function of circRUNX1 as a ceRNAs in PTC progression through miRNA binding. MiR-296-3p was then confirmed to be regulated by circRUNX1 and to target DDHD domain containing 2 (DDHD2) by luciferase reporter assays. The strong antitumor effect of miR-296-3p and the tumor-promoting effect of DDHD2 were further investigated in PTC, indicating that circRUNX1 modulates PTC progression through the miR-296-3p/DDHD2 pathway. Overall, circRUNX1 plays an oncogenic role in PTC and provides a potentially effective therapeutic strategy for PTC progression.

Enhanced osteoclast formation and function have essential roles during post‑menopausal osteoporosis. A number of cytokines have been reported to regulate osteoclastogenesis and to be involved during the pathogenesis of osteoporosis. However, the regulation of osteolysis by microRNAs (miRNAs) has remained to be fully elucidated. The present study used a microarray analysis to identify a variety of miRNAs that are differentially expressed during osteoclast formation. Six down‑regulated miRNAs, miR‑21a‑5p, miR‑27a‑3p, let‑7i‑5p, miR‑22‑3p, miR‑340‑5p and miR‑23a‑5p, whose molecular mechanisms during osteoclast differentiation have not been reported previously, were further assessed. Using an osteoclast formation assay and a mouse model of progressive osteoporosis, the downregulation of these miRNAs was validated in vitro and in vivo. Of note, the expression patterns of these six miRNAs were associated with the progression of osteoporosis. Therefore, these miRNAs are of potential diagnostic and therapeutic value for osteolytic diseases.