Profiles of growth hormone (GH)-regulated genes reveal time-dependent responses and identify a mechanism for regulation of activating transcription factor 3 by GH

In examination of mechanisms regulating metabolic responses to growth hormone (GH), microarray analysis identified 561 probe sets showing time-dependent patterns of expression in GH-treated 3T3-F442A adipocytes. Biological functions significantly over-represented among GH-regulated genes include regulators of transcription at early times, and lipid biosynthesis, cholesterol biosynthesis, and mediators of immune responses at later times (48 h).One novel GH-induced gene encodes activating transcription factor 3 (ATF3). Atf3 mRNA expression and promoter activity were stimulated by GH. Genes for ATF3 and growth arrest and DNA damage-inducible gene 45 gamma (GADD45γ) showed similar time-dependent patterns of responses to GH, suggesting similar regulatory mechanisms. A conserved sequence in the promoters of the Atf3 and Gadd45γ genes contains a CCAAT/enhancer-binding protein (C/EBP) site previously observed in the Gadd45γ promoter, suggesting a novel corresponding C/EBP site in the Atf3 promoter. C/EBPβ was found to bind to the predicted Atf3 C/EBP site, and C/EBPβ enhanced the activation of the wild-type Atf3 promoter. Mutation of the predicted Atf3 C/EBP site disrupted Atf3 promoter activation not only by C/EBPβ but also by GH. These findings suggest that GH regulates transcription of Atf3 through a mechanism utilizing factors, such as C/EBPβ, which bind to a novel C/EBP site.