α1-Adrenergic stimulation of FGF-2 promoter in cardiac myocytes and in adult transgenic mouse hearts (original) (raw)

1999, American Journal of Physiology Heart and Circulatory Physiology

stimulation of FGF-2 promoter in cardiac myocytes and in adult transgenic mouse hearts. Am. J. Physiol. 276 (Heart Circ. Physiol. 45): H826-H833, 1999.-Fibroblast growth factor (FGF-2), a mitogenic, angiogenic, and cardioprotective agent, is reported to be released from the postnatal heart by a mechanism of transient remodeling of the sarcolemma during contraction. This release can be increased with adrenergic stimulation. RNA blotting was used to assess whether FGF-2 synthesis in neonatal rat cardiomyocytes might also be regulated by adrenergic stimulation. FGF-2 RNA levels were increased after treatment with norepinephrine for 6 h or with the ␣-adrenergic agonist phenylephrine for 48 h. To assess an effect on transcription, neonatal rat cardiomyocytes were transfected with a hybrid rat FGF-2 promoter/luciferase gene (Ϫ1058FGFp.luc) and treated with norepinephrine or phenylephrine for 6 or 48 h, respectively. FGF-2 promoter activity was increased two-to sevenfold in an ␣ 1-specific manner. Putative phenylephrine-responsive elements (PEREs) were identified at positions Ϫ780 and Ϫ761 relative to a major transcription initiation site. However, deletion analysis of Ϫ1058FGFp.luc showed that the phenylephrine response was independent of the putative PEREs, cell contraction, and Ca 2ϩ influx. In transgenic mice expressing Ϫ1058FGFp.luc, a significant three-to sevenfold stimulation of FGF-2 promoter activity was detected in the hearts of two independent lines 6 h after intraperitoneal administration of phenylephrine (50 mg/kg). This increase was still apparent at 24 h but was not detected at 48 h posttreatment. Analysis of FGF-2 mRNA in normal mouse hearts revealed accumulation of the 6.1-kb transcript at 24 h. Control of local FGF-2 synthesis at the transcriptional level through adrenergic stimulation may be important in the response to injury as well as in the maintenance of a healthy myocardium. basic fibroblast growth factor; rat fibroblast growth factor-2 gene; phenylephrine; gene transfer FIBROBLAST GROWTH FACTOR (FGF)-2, also known as basic FGF, is a mitogenic and angiogenic protein that has been found in all tissues examined thus far (3, 16). The effects of FGF-2 are exerted through cell-surface, high-affinity tyrosine kinase receptors (FGFR) and low-affinity sites consisting of heparan sulfate proteoglycans (13, 20). Receptors for FGF-2 (FGFR-1) are present in the embryonic and adult heart (15, 17, 22, 23) and were shown to be essential for normal heart development (26). Although FGF-2 is present in the heart into adulthood (15, 23), its role in the postnatal heart is less clear. FGF-2 is found intracellularly as well as outside the cell, where it is able to exert its effect on cell-surface receptors. However, the mechanism for