Stat5b binding elements in the rat <i>Igf1</i> locus confer GH-responsiveness to <i>Igf1</i> promoter 2 in promoter-reporter assays. A

<p>. Diagram of the rat <i>Igf1</i> locus showing seven conserved Stat5b binding elements, R2–4, R8–9, R13, R34–35, R53–54, R57–59, and R60–61. Each element is depicted as a gray oval and the six <i>Igf1</i> exons are shown as black boxes. <b>B</b>. <u>Top</u> - schematic of luciferase reporter plasmids containing rat <i>Igf1</i> promoter 2 (P2) and exon 2, and individual Stat5b binding elements (Enhancer). <u>Bottom</u> - Results of luciferase activity assays in Cos-7 cells transiently transfected with expression plasmids encoding the mouse GH receptor and rat Stat5b and reporter plasmids containing each putative enhancer region diagramed to the <u>left</u> (with each Stat5b site indicated as a white oval, and R13.5 as a gray curved shape), after incubation of cells with vehicle (dark bars) or rat GH [40 nM] (light bars) for 18 h. The graph presents results of 4 independent experiments for each promoter plasmid (mean ± S.E.; *, p<0.01; **, p<0.001 <i>vs.</i> R34–35 without GH [unpaired t-test]). Other p values are indicated, and compare ± GH treatment [paired t-test]. Luciferase counts for R34–35 without GH ranged from 3.5 to 5.5×10³ relative light units/sec.