METTL3-mediated m6A modification of circWDR85 drives breast cancer bone metastasis via the CKB/c-Jun axis.

[BACKGROUND] Bone metastasis is a common and life-threatening complication in advanced breast cancer (BC), yet its underlying molecular mechanisms remain incompletely understood. Circular RNAs (circRNAs) have emerged as critical regulators of tumor progression, including metastasis. Here, we investigated biological role and regulatory mechanism of circWDR85 (hsa_circ_0089696) in BC bone metastasis.

[METHODS] circWDR85 expression and its m6A modification by METTL3 were assessed using RT-qPCR, RIP, MeRIP, and mutational analysis. Functional role of circWDR85 was evaluated via in vitro assays and in vivo intracardiac injection metastasis models. Mechanistic studies were conducted to explore the interaction of circWDR85 with CKB and its effect on c-Jun phosphorylation, ubiquitination, and stability.

[RESULTS] circWDR85 was significantly overexpressed in highly metastatic BC cell lines and bone metastatic tissues. METTL3 directly bound and methylated pre-circWDR85 at a defined m6A site, enhancing its biogenesis. Functionally, circWDR85 promoted bone metastasis in vivo, as its knockdown reduced skeletal lesions and improved survival. Mechanistically, circWDR85 recruited CKB, which directly interacted with c-Jun and facilitated its phosphorylation at T91, thereby stabilizing c-Jun protein by inhibiting ubiquitination. Rescue experiments confirmed that circWDR85 functionally depends on c-Jun activity to drive osteolytic metastasis.

[CONCLUSION] circWDR85 acts as a novel m6A-modified circRNA that promotes BC bone metastasis by stabilizing c-Jun through CKB-mediated phosphorylation.