Role for early growth response-1 protein in alpha(1)-adrenergic stimulation of fibroblast growth factor-2 promoter activity in cardiac myocytes

Fibroblast growth factor-2 (FGF-2), a mitogenic, angiogenic, and cardioprot ective agent, is released from the postnatal heart by a mechanism of transi ent remodelling of the sarcolemma during contraction. Both release of FGF-2 and its synthesis can be increased with adrenergic stimulation. We reporte d previously that FGF-2 synthesis can be regulated at the transcriptional l evel by alpha-adrenergic stimulation of cultured neonatal rat cardiac myocy tes as well as in the adult mouse heart. Examination of the proximal promot er region of both human and rat FGF-2 gene sequences revealed binding sites for the early growth response-1 (Egr-1) protein. Using gel mobility shift assays, we observed a transient increase in a complex between nuclear extra cts from neonatal rat cardiac myocytes treated with inducers of Egr-1, incl uding the alpha-adrenergic agonist phenylephrine, angiotensin II, and phorb ol ester, and a consensus Egr-1 DNA element. A similar complex was seen wit h the FGF-2 promoter region -7/+42 as the DNA probe, but not when the Egr-1 element at nucleotides +3/+31 was disrupted. Participation of Egr-1 protei n in the complex was confirmed by competition with Egr-1 DNA elements and a ntibodies. With deletion analysis and transfection of neonatal rat cardiac myocytes, the alpha-adrenergic response was localized to nucleotides -110/42 of the FGF-2 gene in the context of a hybrid FGF-2/luciferase reporter g ene, -110FGFp.luc. Overexpression of Egr-1 increased -110FGFp.luc gene expr ession, whereas mutation of its Egr-1 element at nucleotides +3/+31 abolish ed alpha-adrenergic responsiveness. These data indicate that Egr-1 is invol ved in the alpha-adrenergic stimulation of the FGF-2 promoter region in neo natal cardiac myocytes.