Integrated Analysis of the mTOR Signaling Pathway Mediated by the ORF3 Protein of Swine Hepatitis E Virus in HepG2 Cells via a circRNA–miRNA Network

Background: The ORF3 protein of swine hepatitis E virus (HEV-4) is a key virulence factor involved in viral assembly, egress, and host signaling regulation. The mammalian target of rapamycin (mTOR) pathway plays a pivotal role in autophagy, metabolism, and immunity, and is often modulated by viruses to promote replication. However, it remains unknown whether HEV-4 ORF3 modulates the mTOR pathway via circular RNAs (circRNAs). Methods: Using an adenovirus-mediated ORF3 overexpression system in HepG2 cells, we integrated circRNA and transcriptome high-throughput sequencing data, followed by KEGG enrichment analysis to identify mTOR-associated differentially expressed genes. A circRNA–miRNA regulatory network was constructed using bioinformatics tools, and the expression changes of m6A-related genes, including YTHDF3, were evaluated. Results: ORF3 overexpression significantly activated the mTOR pathway (p < 0.05) and led to the identification of 20 mTOR-related circRNAs (e.g., circRNA5142). These circRNAs regulated downstream autophagy and lipid metabolism genes by sponging miRNAs such as hsa-let-7d-5p and hsa-miR-132-3p. Altered YTHDF3 expression indicated possible m6A-dependent epitranscriptomic regulation of the mTOR pathway. Conclusions: Our integrated analysis suggests that HEV-4 ORF3 may modulate the mTOR pathway through a circRNA–miRNA network, perturbing host autophagy and metabolic balance, which may contribute to viral immune evasion. Targeting the ORF3-mediated circRNA-mTOR regulatory axis represents a promising therapeutic approach and provides a theoretical basis for novel anti-HEV-4 strategies.