Background: Osteosarcoma (OS) is the most common malignant bone tumor and has a poor prognosis. The potential involvement of circular RNAs (circRNAs) in OS progression remains unexplored. Here, we report that CircECE1, a circular RNA derived from human ECE1, plays a critical role in energy metabolism in OS. Methods: The RIP chip sequence assay was performed to confirm CircECE1, through overexpression or knockdown of CircECE1 to verify its function in 143B and U2OS. RNA immunoprecipitation and immunoprecipitation were used to verify CircECE1’s regulation of protein c-Myc and co- immunoprecipitation was used to verified the competitive binding relationship between CircECE1 and SPOP. The influence of CircECE1 on energy metabolism was evaluated by seahorse experiment, western blot, and immunohistochemistry. Results: We found that CircECE1 is highly expressed in OS tissues and cells and that CircECE1 knockdown suppresses tumor proliferation and metastasis both in vitro and in vivo. Further, CircECE1 significantly promotes glucose metabolism in OS cells in vitro and in vivo. Mechanistically, CircECE1 interacts with c-Myc to prevent speckle-type POZ-mediated c-Myc ubiquitination and degradation. C-Myc inhibits thioredoxin binding protein (TXNIP) transcription and subsequently activates the Warburg effect. Conclusions: CircECE1 regulates the Warburg effect through the c-Myc/TXNIP axis. CircECE1 mediated signal transduction plays a important role in OS process and energy metabolism. These findings may identify novel targets for OS molecular therapy.

Osteoarthritis (OA) is a common joint disease characterized by degradation of the articular cartilage and joint inflammation. Studies have revealed the importance of microRNAs in the regulation of chondrocyte apoptosis. MicroRNA deep sequencing of control and osteoarthritic cartilage has revealed that miR-10a-5p is significantly upregulated in osteoarthritic tissues. However, its role in these tissues remains unknown. The present study was conducted to investigate the effect of miR-10a-5p in promoting OA. miR-10a-5p expression was increased in chondrocytes after interleukin-1β treatment in vitro. Transfection with a miR-10a-5p inhibitor abrogated interleukin-1β-induced apoptosis. A luciferase activity assay showed that miR-10a-5p targeted the 3' UTR of the homeobox gene HOXA1, inhibiting its expression. Treatment with HOXA1 siRNA reversed the rescuing effect of the miR-10a-5p inhibitor on chondrocyte apoptosis. Additionally, an OA model was established in mice by anterior cruciate ligament transection. AntagomiR-10a-5p improved the cartilage surfaces of osteoarthritic mice, whereas agomiR-10a-5p worsened them. A terminal deoxynucleotidyl transferase dUTP nick-end labeling assay indicated reduced apoptosis and increased HOXA1 expression in osteoarthritic mice after miR-10a-5p knockdown. These findings reveal a novel mechanism regulating OA progression and demonstrate the potential of miR-10a-5p and homeobox protein HOXA1 as therapeutic targets.

Bone metastasis is a severe complication of advanced breast cancer, resulting in osteolysis and increased mortality in patients. Raddeanin A (RA), isolated from traditional Chinese herbs, is an oleanane-type triterpenoid saponin with anticancer potential. In this study, we investigated the effects of RA in breast cancer-induced osteolysis and elucidated the possible mechanisms involved in this process. We first verified that RA could suppress osteoclast formation and bone resorption in vitro. Next, we confirmed that RA suppressed Ti-particle-induced osteolysis in a mouse calvarial model, possibly through inhibition of the SRC/AKT signaling pathway. A breast cancer-induced osteolysis mouse model further revealed the positive protective effects of RA by micro-computed tomography and histology. Finally, we demonstrated that RA inhibited invasion and AKT/mammalian target of rapamycin signaling and induced apoptosis in MDA-MB-231 cells. These results indicate that RA is an effective inhibitor of breast cancer-induced osteolysis.

Osteoporosis results from an imbalance between bone formation and bone resorption. Traditional drugs for treating osteoporosis are associated with serious side effects, and thus, new treatment methods are required. This study investigated the role of differentially expressed microRNAs during osteoclast differentiation and osteoclast activity during osteoarthritis as well as the associated underlying mechanisms. We used a microarray to screen microRNAs that decreased in the process of osteoclast differentiation, and verified miR-21-5p to decrease significantly using RT-qPCR. In follow-up experiments, we found that miR-21-5p targets SKP2 to regulate osteoclast differentiation. In vivo, ovariectomised mice were used to simulate perimenopausal osteoporosis induced by oestrogen deficiency, and miR-21-5p treatment inhibited bone resorption and maintained bone cortex and trabecular structure. These results suggest that miR-21-5p is a new therapeutic target for osteoporosis.

Sarcoma, a rare form of cancer, is unlike the much more common carcinomas as it occurs in a distinct type of tissue. The potent antitumor effects of 18β-glycyrrhetinic acid (GA), a novel naturally derived agent, have been demonstrated in various cancers. However, the effect of GA on human sarcoma, and the underlying mechanisms, remain to be elucidated. In the current study, we show that GA inhibits sarcoma cell proliferation by inducing G0/G1-phase arrest. Exposure to GA resulted in the activation of caspase-3, -8, and -9, indicating that GA induced apoptosis through both extrinsic and intrinsic pathways. In addition, the autophagy pathway, characterized by the conversion of LC3-I to LC3- II, was activated, resulting in increased Beclin-1 protein levels, decreased p62 expression, and stimulation of autophagic flux. The present findings showed that GA stimulated autophagy by inducing endoplasmic reticulum (ER) stress via the IRE1–JNK pathway. Our data supported the prosurvival role of GA-induced autophagy when the autophagy pathway was blocked with specific chemical inhibitors. Finally, GA markedly reduced sarcoma growth, with little organ-related toxicity, in vivo. The present results suggest that the combination of GA with a specific autophagy inhibitor represents a promising therapeutic approach for the treatment of sarcoma.