20-HETE regulated PSMB5 expression via TGF-β/Smad signaling pathway

We previously found that 20-hydroxyeicosatetraeonic acid (20-HETE) showed an effect on proteasome activity in cytochrome P450 F2 (CYP4F2) transgenic mice. Proteasome subunit beta 5 (PSMB5) is a primary subunit of the proteasome. In the current study, we examine whether 20-HETE has any affect on PSMB5. We found that PSMB5 was upregulated in the liver, but downregulated in the kidney of transgenic mice, when compared with wild type mice. Luciferase reporter gene experiments and electrophoretic mobility shift assays (EMSA) suggested that Smad3 directly associated with the putative Smad binding element (SBE) of the Pstrtb5 promoter. Furthermore, the binding affinity was different between the liver and kidney, and can be regulated by 20-HETE. Compared to wild mice, both TGF-beta 1 and Smad3 phosphorylation were increased in the liver but decreased in the kidney of transgenic mice. SB431542, an inhibitor of TGF-beta receptor I kinase activity, can reverse the changes induced in PSMB5 by 20-HETE in vitro. Taken together, our data demonstrated that 20-HETE upregulated the expression of PSMB5 by activating the TGF-beta/Smad signaling pathway in the liver, but downregulated the expression of PSMB5 by inhibiting the TGF-beta/Smad signaling pathway in the kidney of transgenic mice.