Exosome-Delivered circFOXP1 Upregulates Autophagy and Promotes Hepatocellular Carcinoma Progression Through Its Encoded p196 Protein Targeting the KHDRBS3/ULK1 Axis.

Introduction: Circular RNAs (circRNAs) are pivotal regulators in cancer, and circFOXP1 has been implicated in tumorigenesis. This study explores the exosome-mediated transfer of circFOXP1 and its functional protein product, p196, in hepatocellular carcinoma (HCC) progression. Methods: HCC circRNA datasets were obtained from the Gene Expression Omnibus (GEO) databases, and circRNAs were validated via qRT-PCR and Sanger sequencing. Exosomes were isolated via ultracentrifugation and characterized by TEM/NTA. RIP, Co-IP, RNA pull-down and in vitro binding assays were employed to determine molecular interactions. Loss- and gain-of-function assays were employed to evaluate the effects of circFOXP1, KHDRBS3 and ULK1 on the proliferation, and invasion abilities of HCC cells both in vitro and in vivo. Results: CircFOXP1, which encoded a 196-amino acid protein, p196, was highly expressed in HCC tissues and cells and secreted via exosomes. Overexpression of p196 enhanced HCC cell proliferation, invasion, and autophagy flux in vitro, while knockdown produced opposite effects. Mechanistically, p196 directly bound KHDRBS3 through its D2 domain, forming a complex that stabilized ULK1 mRNA, thereby increasing ULK1 protein levels, activating autophagy and accelerating tumor progression. Conclusion: Our findings indicated that circFOXP1-encoded p196 plays a role as a tumor promoter, contributing to the malignant progression of HCC. Targeting the circFOXP1/p196-KHDRBS3-ULK1 axis presents a promising therapeutic strategy for HCC, with potential applications in biomarker development and combination therapies.