m6A-dependent translation of circPICALM encodes a novel metastasis-promoting oncoprotein in intrahepatic cholangiocarcinoma.

BACKGROUND: Intrahepatic cholangiocarcinoma (ICC) is a highly aggressive liver cancer with a poor prognosis and rapid metastatic potential. Although circular RNAs (circRNAs) have emerged as important regulators in cancer biology, their translational potential and mechanistic contributions to ICC metastasis remain largely unexplored. METHODS: CircRNA-seq was performed on paired primary and recurrent ICC tissues to identify the differentially expressed circRNAs. Mass spectrometry and functional assays were used to characterize the novel protein encoded by circPICALM. The molecular mechanisms and biological functions of circPICALM and its encoded proteins were evaluated using in vitro and in vivo models, respectively. RESULTS: CircPICALM is significantly upregulated in recurrent ICC tumors and is associated with poor patient prognosis. Its biogenesis and expression are regulated by N6-methyladenosine (m6A) modifications within the introns flanking the circulating exons, facilitated by the m6A reader protein YTHDC1. Additionally, the RNA-binding protein, DEAD-box helicase 3 (DDX3), promotes circPICALM accumulation. Importantly, circPICALM encodes a novel protein, circPICALM-219aa, that drives ICC metastasis. Mechanistically, circPICALM-219aa disrupted the inhibitory interaction between SOCS3 and STAT3 by directly binding to both proteins. This interference alleviates SOCS3-mediated suppression of JAK activity and enhances IL-6/JAK/STAT3 signaling. Silencing circPICALM-219aa expression significantly suppressed the activation of this signaling pathway and metastatic potential. CONCLUSIONS: This study identified circPICALM-219aa as a novel oncoprotein translated from an m6A-modified circRNA, and a key driver of ICC metastasis. Our findings uncover a previously unrecognized mechanism of m6A-mediated circRNA translation in ICC and highlight circPICALM-219aa as a promising therapeutic target for improving patient outcomes.