Transcriptional regulation of FGF-2 gene expression in cardiac myocytes.
OBJECTIVE
Fibroblast growth factor-2 (FGF-2) exerts its cardioprotective effect through cell surface receptor signaling and may play a role in the normal maintenance of a healthy myocardium. One mechanism of FGF-2 release from contracting cardiomyocytes is through transient sarcolemmal disruption, with accumulation in the extracellular matrix. Continuous FGF-2 release would require a link to synthesis and, thus, we examined regulation of FGF-2 promoter activity in cardiomyocytes as a potential target for optimizing cardioprotection.


RESULTS
To investigate autoregulation, neonatal rat cardiomyocytes, (NRCM), were transfected with approximately 1 or 0.1 kb of rat FGF-2 promoter sequences linked to luciferase, -1058FGF-2p.luc and -110FGF-2p.luc, and treated with or without FGF-2. FGF-2 promoter activity was significantly increased approximately 2.5-fold with both genes. The proximal promoter region of rat FGF-2 contains putative binding sites for the early growth response-1 (Egr-1) and stimulating protein 1 (Sp1) transcription factors. Overexpression of Egr-1 and Sp1 increased -1058FGF-2p.luc expression by 4.4- and 8.7-fold, respectively. Mutation of Egr-1 and overlapping Sp1 sites did not blunt the response of -110FGF-2p.luc to FGF-2 treatment but did significantly reduce basal promoter activity. Transgenic mice expressing -1058FGF-2p.luc were treated with isoproterenol (IsP) to increase heart rate and endogenous FGF-2 release. FGF-2 promoter activity was stimulated significantly at 6 h, and increases in both FGF-2 and its receptor mRNA levels were also detected. In contrast, no effect of IsP was seen on -1058FGF-2p.luc or -110FGF-2p.luc in transfected NRCMs.


CONCLUSIONS
FGF-2 released from cardiomyocytes may act to regulate its own synthesis at the transcriptional level. The mechanism does not appear to require an intact Egr-1 site in the proximal promoter region. This may, however, reflect redundancy in the control of FGF-2 promoter activity as our data support a stimulatory role for Egr-1 and Sp1.
Jimenez
Sarah K
SK
Department of Physiology, University of Manitoba, 730 William Avenue, Winnipeg, MB, Canada R3E 3J7.
Sheikh
Farah
F
Jin
Yan
Y
Detillieux
Karen A
KA
Dhaliwal
Jamit
J
Kardami
Elissavet
E
Cattini
Peter A
PA
D000318:Adrenergic beta-Agonists / Q000494:pharmacology; D000818:Animals; D002478:Cells, Cultured; D024202:Electrophoretic Mobility Shift Assay; D016222:Fibroblast Growth Factor 2 / Q000235:genetics* / Q000494:pharmacology; D005786:Gene Expression Regulation; D007545:Isoproterenol / Q000494:pharmacology; D051379:Mice; D008822:Mice, Transgenic; D032383:Myocytes, Cardiac / Q000187:drug effects / Q000378:metabolism*; D011401:Promoter Regions, Genetic; D051381:Rats; D020794:Receptor Protein-Tyrosine Kinases / Q000032:analysis; D051496:Receptor, Fibroblast Growth Factor, Type 1; D017468:Receptors, Fibroblast Growth Factor / Q000032:analysis; D014158:Transcription, Genetic
D000318:Adrenergic beta-Agonists; D017468:Receptors, Fibroblast Growth Factor; D016222:Fibroblast Growth Factor 2; C496349:Fgfr1 protein, mouse; C496350:Fgfr1 protein, rat; D020794:Receptor Protein-Tyrosine Kinases; D051496:Receptor, Fibroblast Growth Factor, Type 1; D007545:Isoproterenol