Role of HMGA1 in basal and cAMP-induced RBP4 expression. Rbp4-Luc reporter vector and HMGA1 expression plasmid (sense or antisense) were cotransfected into Hepa1 and HEK-293 cells, either untreated or treated with Br-cAMP. Data represent the means ± standard errors for three separate experiments. Transcriptional activity of the RBP4 gene promoter is shown as the ratio of luciferase activity to Renilla activity (Luc/Ren) as described in the experimental procedures. Values are expressed as the factors by which induced activity increased above the level of Luc activity obtained in transfections with the reporter vector alone, which is assigned an arbitrary value of 1. Open bar, mock (no DNA); black bar, pGL3-basic (vector without an insert). Western blots of HMGA1 and β-actin in each condition are shown in the autoradiograms.