Transcriptional activation of the BNP gene by lipopolysaccharide is mediated through GATA elements in neonatal rat cardiac myocytes.
Lipopolysaccharide (LPS) has a profound effect on cardiac performance through a collapse of the vasculature. In this study, we determined whether LPS has a direct effect on the cardiac myocytes by examining the expression of the BNP gene in cultured neonatal rat cardiac myocytes. Northern blot analysis showed that LPS induces the expression of the BNP gene. Time-course experiments revealed that BNP mRNA levels were increased 1 h after LPS stimulation. Enhanced induction of BNP was observed 3 h after stimulation when expression of CD14, a specific receptor for LPS, was markedly induced. LPS-mediated BNP expression was completely inhibited by the pretreatment of SB203580, a specific inhibitor for p38 MAPK as well as by genistein, a broad range tyrosine kinase inhibitor. In accordance with these results, LPS increases phosphorylation of p38 mitogen-activated protein kinase (MAPK). Transient transfection assays revealed that low dose (1 ng/ml) of LPS induces the luciferase activity derived from the construct containing the BNP promoter spanning from -1000 and +80 in front of the luciferase gene. Cotransfection of the expression vectors for constitutive active forms of Rac1, MKK3 and p38 MAPK significantly increased BNP promoter activity. Mutation of the GATA sequence located at -95 and -84 abolished such an induction of BNP promoter activity. Overexpression of CD14 enhanced the LPS's effect on BNP promoter. These results indicate that LPS induces the BNP gene expression through a pathway involving CD14, Rac1, p38 MAPK and GATA elements. In addition to the induction of BNP expression by hemodynamic overload, our data suggest that elevated levels of BNP under the endotoxemic condition is partly mediated through the increased expression of CD14, which lies upstream of the Rac1-p38 MAPK pathway.
Tomaru Ki
Kou-ichi
K
Second Department of Internal Medicine, Gunma University School of Medicine, Japan.
Arai
Masashi
M
Yokoyama
Tomoyuki
T
Aihara
Yasushi
Y
Sekiguchi Ki
Ken-ichi
K
Tanaka
Toru
T
Nagai
Ryozo
R
Kurabayashi
Masahiko
M
D000818:Animals; D009320:Atrial Natriuretic Factor / Q000235:genetics*; D002478:Cells, Cultured; D005786:Gene Expression Regulation; D007375:Interleukin-1 / Q000378:metabolism; D018950:Lipopolysaccharide Receptors / Q000235:genetics / Q000378:metabolism; D008070:Lipopolysaccharides / Q000494:pharmacology*; D020935:MAP Kinase Signaling System / Q000502:physiology; D008297:Male; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D032383:Myocytes, Cardiac / Q000378:metabolism*; D020097:Natriuretic Peptide, Brain; D011401:Promoter Regions, Genetic; D011505:Protein-Tyrosine Kinases / Q000378:metabolism; D051381:Rats; D020218:Response Elements; D014158:Transcription, Genetic; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism; D048051:p38 Mitogen-Activated Protein Kinases; D020744:rac GTP-Binding Proteins / Q000378:metabolism
D007375:Interleukin-1; D018950:Lipopolysaccharide Receptors; D008070:Lipopolysaccharides; D014409:Tumor Necrosis Factor-alpha; D020097:Natriuretic Peptide, Brain; D009320:Atrial Natriuretic Factor; D011505:Protein-Tyrosine Kinases; D020928:Mitogen-Activated Protein Kinases; D048051:p38 Mitogen-Activated Protein Kinases; D020744:rac GTP-Binding Proteins