Caveolin‐1‐dependent activation of the metalloprotease TACE / ADAM 17 by TGF ‐β in hepatocytes requires activation of Src and the NADPH oxidase NOX 1

Transforming growth factor‐β ( TGF ‐β) plays a dual role in hepatocytes, inducing both pro‐ and anti‐apoptotic responses, the balance between which decides cell fate. Survival signals are mediated by the epidermal growth factor receptor ( EGFR ) pathway, which is activated by TGF ‐β. We have previously shown that caveolin‐1 ( CAV 1) is required for activation of the metalloprotease tumour necrosis factor ( TNF )‐α‐converting enzyme/a disintegrin and metalloproteinase 17 ( TACE / ADAM 17), and hence transactivation of the EGFR pathway. The specific mechanism by which TACE / ADAM 17 is activated has not yet been determined. Here we show that TGF ‐β induces phosphorylation of sarcoma kinase (Src) in hepatocytes, a process that is impaired in Cav1 −/− hepatocytes, coincident with a decrease in phosphorylated Src in detergent‐resistant membrane fractions. TGF ‐β‐induced activation of TACE / ADAM 17 and EGFR phosphorylation were blocked using the Src inhibitor PP 2. Cav1 +/+ hepatocytes showed early production of reactive oxygen species ( ROS ) induced by TGF ‐β, which was not seen in Cav1 −/− cells. Production of ROS was inhibited by both the NADPH oxidase 1 ( NOX 1) inhibitor STK 301831 and NOX 1 knock‐down, which also impaired TACE / ADAM 17 activation and thus EGFR phosphorylation. Finally, neither STK 301831 nor NOX 1 silencing impaired Src phosphorylation, but PP 2 blocked early ROS production, showing that Src is involved in NOX 1 activation. As expected, inhibition of Src or NOX 1 increased TGF ‐β‐induced cell death in Cav1 +/+ cells. In conclusion, CAV 1 is required for TGF ‐β‐mediated activation of TACE / ADAM 17 through a mechanism that involves phosphorylation of Src and NOX 1‐mediated ROS production.