P155
Brain natriuretic peptide (BNP) gene expression accompanies cardiac hypertrophy and heart failure. The vasoconstrictor endothelin-1 (ET)may be involved in the development of these diseases. ET has also been shown to activate phospholipase A
2
(PLA
2
). Thus we studied whether ET and PLA
2
metabolites regulate BNP gene expression. The hBNP promoter (-1818 to + 100) coupled to a luciferase reporter gene was transferred into neonatal ventricular myocytes (NVM),and luciferase activity was measured as an index of promoter activity. ET (10
-7
M)induced BNP mRNA in NVM as assessed by Northern blot. It also stimulated the hBNP promoter 4-fold vs control, an effect completely inhibited by actinomycin D. To test the involvement of different PLA
2
isoforms, transfected cells were treated with the Ca
++
-independent PLA
2
(iPLA
2
)inhibitor bromoenol lactone (BEL), the cytosolic PLA
2
inhibitor methyl arachidonyl fluorophosphonate, or the secretory PLA
2
inhibitor ONO-RS-082 prior to stimulation with ET. Only the iPLA
2
inhibitor BEL prevented ET-stimulated hBNP promoter activity. The PLA
2
metabolite lysophosphatidic acid (LPA) also activated the hBNP promoter (2.2-fold; n = 3), but lysophosphatidylcholine did not. To test whether arachidonic acid metabolites are involved in ET’s effect, cells were pretreated with either a lipoxygenase (LO), cyclooxygenase, or p450 monooxygenase inhibitor. Only the LO inhibitor baicalein prevented ET stimulation of the hBNP promoter. Finally, we studied the involvement of
cis
elements in ET-stimulated hBNP promoter activity. Deletion of BNP promoter sequences from -1818 to -408 and from -408 to -40 reduced ET’s effect by 54% and 78%, respectively. Moreover, ET-stimulated luciferase activity was reduced by 53% when the GATA element (at position -85 relative to the start site of transcription) was mutated. These data suggest that: 1) ET activates the hBNP promoter through a transcriptional mechanism; 2) LPA, perhaps generated by a BEL-sensitive iPLA
2
, is involved in ET’s effect; 3) a LO pathway may also mediate ET signaling; and 4) ET regulation of the hBNP promoter targets both distal and proximal
cis
elements, including GATA.