N6-methyladenosine modification promotes hepatocarcinogenesis through circ-CDYL-enriched and EpCAM-positive liver tumor-initiating exosomes.

CircRNAs play multiple roles in a variety of cellular processes. We found that Circ-CDYL is highly enriched in early HCC plasma exosomes. Moreover, EpCAM HCC cells and exosomes had significant Circ-CDYL levels. We postulated that Circ-CDYL-enriched and EpCAM-positive exosomes would function as liver tumor-initiating exosomes (LTi-Exos). As predicted, intercellular transfer of LTi-Exos activates the HDGF-PI3K-AKT-mTOR and HIF1AN-NOTCH2 axes in recipient cells, promoting malignancy. Upstream, we found that the N6-methyladenosine (mA) modification of Circ-CDYL exerted its action in HCC cells through a dual mechanism. First, it stimulated back-splicing processes via YTHDC1 to promote Circ-CDYL biogenesis. Second, it facilitates the active sorting of Circ-CDYL into exosomes via hnRNPA2/B1. Clinically, the combination of LTi-Exos and plasma alpha-fetoprotein (AFP) provides a promising early diagnostic biomarker for HCC with an AUC of 0.896. This study highlights the effect and mechanism by which mA modification promotes hepatocarcinogenesis via modulation of the tumor microenvironment by LTi-Exos.