ATF3-SLC7A7 Axis Regulates mTORC1 Signaling to Suppress Lipogenesis and Tumorigenesis in Hepatocellular Carcinoma

Background Hepatocellular carcinoma (HCC) remains a major global health challenge with poor prognosis and high mortality. Dysregulated lipid metabolism is increasingly recognized as a key driver of HCC progression. While the transcription factor ATF3 has been implicated in tumorigenesis and lipid regulation, its precise role in HCC development and lipid biosynthesis is not fully understood. Methods We generated ATF3-overexpression and ATF3-knockdown HCC cell lines via lentiviral infection. To investigate ATF3’s role in HCC, we performed in vitro assays, including MTT, transwell migration, wound healing, and colony formation assays, alongside an in vivo mouse xenograft model to assess tumor growth. The correlation between ATF3 expression and lipid synthesis was analyzed using RNA-Seq data from HCC patients and further validated by qRT-PCR, Nile Red staining, lipid quantification, correlation analysis, and immunohistochemistry. The impact of ATF3 on mTORC1 signaling was evaluated through western blotting, confocal microscopy, Oil Red O staining, and lipid quantification assays. SLC7A7, identified as a potential downstream effector of ATF3, was analyzed using qRT-PCR, and its influence on mTORC1 signaling was examined in the same manner as ATF3. The binding of ATF3 to the enhancer region of SLC7A7 was identified via ChIP-Seq and confirmed through ChIP-qPCR, luciferase reporter assays, and DNA pull-down assays. Results We demonstrate that mTORC1 inhibition markedly reduces lipogenesis in HCC and identify a regulatory axis involving ATF3 and the amino acid transporter SLC7A7. Transcriptomic analysis reveals an inverse correlation between ATF3 expression and lipid synthesis, a finding supported by experimental data. Mechanistically, ATF3 represses mTORC1 signaling, inhibiting lipid biosynthesis, with SLC7A7 acting as a key mediator. ATF3 directly binds to the enhancer region of SLC7A7, activating its transcription and subsequently limiting mTORC1 activity. Functional assays in ATF3-overexpression and -knockdown HCC cell lines confirm ATF3’s tumor-suppressive role. Conclusion This study uncovers a novel ATF3-SLC7A7-mTORC1 regulatory axis that mitigates lipogenesis and tumorigenesis in HCC, highlighting a critical link between lipid metabolism and liver cancer progression. These findings present promising therapeutic targets for HCC treatment.