A positive feedback circuit driven by m6A-modified circular RNA facilitates colorectal cancer liver metastasis.

ABSTRACT

BACKGROUND: Liver metastasis is the leading cause of death in patients with colorectal cancer (CRC). Emerge evidence suggests that circular RNA (circRNA) is a pivotal player in cancer progression. However, its role in CRC liver metastasis remains largely unknown. METHODS: Circ-YAP expression was detected by qRT-PCR and in situ hybridization. The function of circ-YAP was tested by wound healing, transwell and CCK-8 assays. RNA immunoprecipitation, pull-down, luciferase reporter, chromatin immunoprecipitation assays were used to investigate the mechanism underlying circ-YAP promoting CRC liver metastasis. CRC liver metastasis animal model was established to assess the effect of circ-YAP in vivo. RESULTS: Circ-YAP was notably upregulated in CRC with liver metastasis, which was associated with dismal prognosis. Circ-YAP promoted CRC cell migration and invasion in vitro, and facilitated liver metastasis in patient-derived xenografts (PDX) models in vivo. Mechanistically, circ-YAP encoded a novel truncated protein containing 220 amino acids, termed as YAP-220aa, which competitively bound to LATS1, resulting in YAP dephosphorylation and nuclear translocation, thereby activating a cohort of metastasis-promoting genes. Importantly, N6-methyladenosine (m6A) modification orchestrated efficient initiation of circ-YAP translation, requiring m6A reader YTHDF3 and eIF4G2 translation initiation complex. Intriguingly, circ-YAP was transcriptionally enhanced by YAP/TEAD complex, thus forming a positive regulatory feed-forward loop. CONCLUSIONS: Our findings reveal a previously uncharacterized oncoprotein encoded by circ-YAP, implying a promising biomarker and therapeutic target for CRC patients with liver metastasis.