Loss of Ufl1/Ufbp1 in hepatocytes promotes liver pathological damage and carcinogenesis through activating mTOR signaling.

BACKGROUND

Ufm1-specific ligase 1 (Ufl1) and Ufm1-binding protein 1 (Ufbp1), as putative targets of ubiquitin-fold modifier 1 (Ufm1), have been implicated in several pathogenesis-related signaling pathways. However, little is known about their functional roles in liver disease.

METHODS

Hepatocyte-specific Ufl1Δ/Δhep and Ufbp1Δ/Δhep mice were used to study their role in liver injury. Fatty liver disease and liver cancer were induced by high-fat diet (HFD) and diethylnitrosamine (DEN) administration, respectively. iTRAQ analysis was employed to screen for downstream targets affected by Ufbp1 deletion. Co-immunoprecipitation was used to determine the interactions between the Ufl1/Ufbp1 complex and the mTOR/GβL complex.

RESULTS

Ufl1Δ/Δhep or Ufbp1Δ/Δhep mice exhibited hepatocyte apoptosis and mild steatosis at 2 months of age and hepatocellular ballooning, extensive fibrosis, and steatohepatitis at 6-8 months of age. More than 50% of Ufl1Δ/Δhep and Ufbp1Δ/Δhep mice developed spontaneous hepatocellular carcinoma (HCC) by 14 months of age. Moreover, Ufl1Δ/Δhep and Ufbp1Δ/Δhep mice were more susceptible to HFD-induced fatty liver and DEN-induced HCC. Mechanistically, the Ufl1/Ufbp1 complex directly interacts with the mTOR/GβL complex and attenuates mTORC1 activity. Ablation of Ufl1 or Ufbp1 in hepatocytes dissociates them from the mTOR/GβL complex and activates oncogenic mTOR signaling to drive HCC development.

CONCLUSIONS

These findings reveal the potential role of Ufl1 and Ufbp1 as gatekeepers to prevent liver fibrosis and subsequent steatohepatitis and HCC development by inhibiting the mTOR pathway.