Abstract |
Increased expression of the inhibitory G protein Gi alpha-2 is assumed to contribute to desensitization of adenylyl cyclase in human heart failure. The mechanisms of upregulation involve increases in myocardial Gi alpha-2 protein, mRNA and gene transcriptional activity. To elucidate these mechanisms in more detail, the 5' flanking region of the human Gi alpha-2 gene (-1214/+115 bp) was cloned upstream of the bacterial chloramphenicol acetyltransferase (CAT) gene and transfected in embryonic chick cardiomyocytes. CAT activity was measured 48 h after transfection. Unstimulated activity of the -1214/+115 bp construct was about 10-fold higher than activity of the basal CAT-construct (pGEMCAT). 5' deletion from -1214/+115 to -85/+115 bp upstream of the transcriptional start site increased, further stepwise deletions to 46/+115 gradually decreased promotor activity. Deletion from -46/+115 to -33/+115 bp completely abolished promotor activity. Stimulation of cardiomyocytes that had been transfected with the -1214/+115 CAT-construct with isoprenaline (10 microM), forskolin (10 microM), forskolin (10 microM) plus IBMX (10 microM) or dibutyryl-cAMP (1 mM) for 24 h induced an increase in CAT activity to 139 +/- 12% (n = 9), 211 +/- 18% (n = 12), 256 +/- 20% (n = 5) and 198 +/- 28% (n = 7) of unstimulated values, respectively. We conclude: 1) In chicken cardiomyocytes a sequence element of 52 bp between -85 and -33 bp is necessary to provide basal Gi alpha-2 promotor activity. 2) Elevation of cAMP has a stimulatory effect on the human Gi alpha-2 promotor, thereby offering a mechanism for beta- adrenoceptor-mediated increases in Gi alpha-2 in the heart.
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Authors | T Eschenhagen, M Friedrichsen, S Gsell, A Hollmann, C Mittmann, W Schmitz, H Scholz, J Weil, L S Weinstein |
Journal | Basic research in cardiology
(Basic Res Cardiol)
Vol. 91 Suppl 2
Pg. 41-6
( 1996)
ISSN: 0300-8428 [Print] Germany |
PMID | 8957543
(Publication Type: Journal Article)
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Chemical References |
- RNA, Messenger
- Colforsin
- Bucladesine
- Cyclic AMP
- Chloramphenicol O-Acetyltransferase
- GTP-Binding Protein alpha Subunits, Gi-Go
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Topics |
- Animals
- Bucladesine
(pharmacology)
- Cells, Cultured
- Chick Embryo
- Chloramphenicol O-Acetyltransferase
(metabolism)
- Colforsin
(pharmacology)
- Cyclic AMP
(metabolism)
- GTP-Binding Protein alpha Subunits, Gi-Go
(genetics, metabolism)
- Heart
(drug effects, embryology)
- Humans
- Mutation
- Myocardium
(cytology, metabolism)
- Plasmids
(genetics)
- Promoter Regions, Genetic
- RNA, Messenger
(genetics)
- Transfection
- Up-Regulation
(genetics)
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