GDF11 regulates the EGF signal transduction pathway.

<p>(<b>A</b>) Q-PCR analysis of EGFR transcript levels in Cor-1 cells incubated with either control vehicle or 25 ng/ml GDF11 for 3 hr. EGF receptor expression is normalised against two housekeeping genes, GAPDH or HPRT. GDF11 significantly downregulates EGF receptor transcript levels (mean ± SEM; **<i>p</i><0.01, n = 6). (<b>B</b>) Cor-1 cells incubated with 25 or 50 ng/ml GDF11 for either 24 or 48 hr were lysed and analysed for EGFR levels by Western blot. Exposure to GDF11 significantly decreases EGF receptor protein levels as shown by densitometric analysis relative to actin (mean ± SEM; *<i>p</i><0.05, **<i>p</i><0.01, n = 3) and by a representative blot. (<b>C</b>) Cor-1 cells were transiently co-transfected with a luciferase reporter construct and a <i>Renilla</i> plasmid by nucleofection. Twenty hours later cells were pre-incubated with 50 ng/ml GDF11 for 36 h before being starved of EGF and FGF for 6 h to reduce endogenous pCREB levels. Cells were then challenged with 10 ng/ml EGF and luciferase expression was subsequently measured by addition of a luciferase substrate. Transfection efficiency and cell numbers were taken into account by normalising luciferase readings at 570 nm against <i>Renilla</i> activity (detected by measuring light emission at 480 nm) (mean ± SEM; ***<i>p</i><0.001, n = 3).