Circ_0002669 promotes osteosarcoma tumorigenesis through directly binding to MYCBP and sponging miR-889-3p

Circular RNAs (circRNAs) are a class of highly multifunctional single-stranded RNAs that play crucial roles in cancer progression, including osteosarcoma (OS). Circ_0002669, generated from the dedicator of cytokinesis (DOCK) gene, was highly expressed in OS tissues, and negatively correlated with OS patient survival. Elevated circ_0002669 promoted OS cell growth and invasion in vivo and in vitro. By biotin pulldown and mass spectroscopy, we found that circ_0002669 directly bound to MYCBP, a positive regulator of c-myc, to prevent MYCBP from ubiquitin-mediated proteasome degradation. In addition, circ_0002669 interacted with miR-889-3p and served as a miRNA sponge to increase the expression of MYCBP, as determined by luciferase assays and RNA immunoprecipitation. Functional rescue experiments indicated MYCBP acted as a key factor for circ_0002669- and miR-889-3p-regulated OS cell proliferation and migration. Increased expression of c-myc-associated genes, such as CCND1, c-Jun and CDK4, were found in circ_0002669- and MYCBP-overexpressing OS cells. Our data thus provide evidence that circ_0002669 promotes OS malignancy by protecting MYCBP from protein ubiquitination and degradation and blocking miR-889-3p-mediated inhibition of MYCBP expression.

A tumor suppressor protein encoded by circKEAP1 inhibits osteosarcoma cell stemness and metastasis by promoting vimentin proteasome degradation and activating anti-tumor immunity

BACKGROUND

Osteosarcoma (OS) is one of most commonly diagnosed bone cancer. Circular RNAs (circRNAs) are a class of highly stable non-coding RNA, the majority of which have not been characterized functionally. The underlying function and molecular mechanisms of circRNAs in OS have not been fully demonstrated.

METHOD

Microarray analysis was performed to identify circRNAs that are differentially-expressed between OS and corresponding normal tissues. The biological function of circKEAP1 was confirmed in vitro and in vivo. Mass spectrometry and western blot assays were used to identify the circKEAP1-encoded protein KEAP1-259aa. The molecular mechanism of circKEAP1 was investigated by RNA sequencing and RNA immunoprecipitation analyses.

RESULTS

Here, we identified a tumor suppressor circKEAP1, originating from the back-splicing of exon2 of the KEAP1 gene. Clinically, circKEAP1 is downregulated in OS tumors and associated with better survival in cancer patients. N6-methyladenosine (m6A) at a specific adenosine leads to low expression of circKEAP1. Further analysis revealed that circKEAP1 contained a 777 nt long ORF and encoded a truncated protein KEAP1-259aa that reduces cell proliferation, invasion and tumorsphere formation of OS cells. Mechanistically, KEAP1-259aa bound to vimentin in the cytoplasm to promote vimentin proteasome degradation by interacting with the E3 ligase ARIH1. Moreover, circKEAP1 interacted with RIG-I to activate anti-tumor immunity via the IFN-γ pathway.

CONCLUSION

Taken together, our findings characterize a tumor suppressor circKEAP1 as a key tumor suppressor regulating of OS cell stemness, proliferation and migration, providing potential therapeutic targets for treatment of OS.

LncRNA WAC-AS1 promotes osteosarcoma Metastasis and stemness by sponging miR-5047 to upregulate SOX2

Cancer stemness and osteosarcoma (OS) malignant progression are closely associated. However, the molecular mechanisms underlying this association have not been fully demonstrated. Long noncoding RNAs (lncRNAs) are an intriguing class of widely prevalent endogenous RNAs involved in OS progression, the vast majority of which have not been characterized functionally. Here, we identified tumor promoter lncRNA WAC-AS1 to be highly expressed in OS tumors and associated with worse survival. Further analysis revealed that WAC-AS1 increased tumorsphere formation of OS cells and promoted metastasis, as confirmed by cell proliferation, transwell and wound healing assays. MiR-5047 was identified as a downstream target of WAC-AS1. Subsequently, based on bioinformatics analysis, RIP assay and luciferase reporter assay, SOX2 mRNA was verified as a target of miR-5047. WAC-AS1 enhanced OS cell proliferation and stemness via acting as a ceRNA by binding to miR-5047, thereby increasing SOX2 expression. In addition, SOX2 bound to the promoter region of WAC-AS1 and promoted its transcription, thereby forming a positive feedback loop to regulate OS malignancy. Taken together, our findings show WAC-AS1 is a tumor promoter and a key regulator of OS cell stemness and metastasis via a miR-5047/SOX2 axis.