CYP3A5 is a cytochrome P450 protein that functions in the liver metabolism of many carcinogens and cancer drugs. However, it has not been thought to directly affect cancer progression. In this study, we challenge this perspective by demonstrating that CYP3A5 is downregulated in many hepatocellular carcinomas (HCC), where it has an important role as a tumor suppressor that antagonizes the malignant phenotype. CYP3A5 was downregulated in multiple cohorts of human HCC examined. Lower CYP3A5 levels were associated with more aggressive vascular invasion, poor differentiation, shorter time to disease recurrence after treatment, and worse overall patient survival. Mechanistic investigations showed that CYP3A5 overexpression limited MMP2/9 function and suppressed HCC migration and invasion in vitro and in vivo by inhibiting AKT signaling. Notably, AKT phosphorylation at Ser473 was inhibited in CYP3A5-overexpressing HCC cells, an event requiring mTORC2 but not Rictor/mTOR complex formation. CYP3A5-induced ROS accumulation was found to be a critical upstream regulator of mTORC2 activity, consistent with evidence of reduced GSH redox activity in most clinical HCC specimens with reduced metastatic capacity. Taken together, our results defined CYP3A5 as a suppressor of HCC pathogenesis and metastasis with potential utility a prognostic biomarker.
©2015 American Association for Cancer Research.