Regulation of sterol 27-hydroxylase in human monocyte-derived macrophages: up-regulation by transforming growth factor β1

Regulatory mechanisms for human CYP27A1 enzyme have not yet been fully investigated. Our approach was to add different hormones and cytokines to cultured human monocyte-derived macrophages, and assess the effects on the CYP27A1 by measuring the production of 27-hydroxylated cholesterol in the media. Of the different hormones and cytokines tested, only transforming growth factor β1 (TGF-β1) had a clear effect on CYP27A1. Further experiments showed a significant increase in 27-hydroxylated cholesterol products (27-hydroxycholesterol and 3β-hydroxy-5-cholestenoic acid). A concomitant increase in CYP27A1 mRNA levels was also seen and this positive effect was confirmed using a human CYP27A1 luciferase reporter gene expressed in HepG2 cells. Experiments with progressive deletion/luciferase reporter gene constructs indicated that a TGF-β1 responsive sequence might be localized in a region about 400 bp upstream of the CYP27A1 translation start. The possibility is discussed that induction of CYP27A1 by TGF-β1 may be responsible for some of the anti-atherogenic properties of this cytokine.