CircEPHB4 binds to YBX1 to upregulate MRPS16 and promotes glioma progression.

BACKGROUND: Glioma is the most frequently diagnosed brain tumor in adults worldwide which is associated with unfavorable prognosis and survival time. However, the understanding of glioma progression remains limited. METHODS: The cell proliferation in glioma cells were monitored by EdU incorporation and CCK-8 assays. Glioma cell invasion and migration were assessed by Transwell assay. In vivo tumorigenesis were detected by xenograft study with bioluminescence imaging. qRT-PCR, RNA FISH, IHC or western blot were used to detect circEPHB4, MRPS16, YBX1, RBBP6 and other molecules expression. The associations between YBX1 and MRPS16 mRNA, as well as between circEPHB4 and YBX1, were detected by RNA immunoprecipitation (RIP) and RNA pull-down assays. In addition, the ubiquitination of YBX1 and RBBP6-YBX1 interaction were assessed by co-immunoprecipitation (co-IP). RESULTS: Knockdown of circEPHB4 or MRPS16 inhibited glioma progression in vitro and in vivo. circEPHB4 promoted glioma cell proliferation, migration, and invasion via increasing MRPS16 expression in vitro. At the post-transcriptional level, circEPHB4 enhanced MRPS16 mRNA stability through YBX1-mediated m(5)C modification in vitro. At the post-translational level, RBBP6 catalyzed the ubiquitination of YBX1, and circEPHB4 competed with RBBP6 to bind YBX1 to inhibit the ubiquitin-proteasomal degradation of YBX1 in vitro. circEPHB4 interacted with YBX1 to promote glioma cell growth via inducing MRPS16 in vitro and in vivo. CONCLUSION: circEPHB4 bound to YBX1 to inhibit RBBP6-mediated degradation and increase its expression, thus enhancing MRPS16 mRNA stability via m(5)C modification, and ultimately promoting glioma progression.