Abstract
Increased expression of the inhibitory G protein Giα-2 is assumed to contributed to desensitization of adenylyl cyclase in human heart failure. The mechanisms of upregulation involve increases in myocardial Giα-2 protein, mRNA and gene transcriptional activity. To elucidate these mechanisms in more detail, the 5′ flanking region of the human Giα-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 10fold 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 μM), forskolin (10 μM), forskolin (10 μM) plus IBMX (10 μM) 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 Giα-2 promotor activity. 2) Elevation of cAMP has a stimulatory effect on the human Giα-2 promotor, thereby offering a mechanism for β-adrenoceptor-mediated increases in Giα-2 in the heart.
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Eschenhagen, T., Friedrichsen, M., Gsell, S. et al. Regulation of the human Giα-2 gene promotor activity in embryonic chicken cardiomyocytes. Basic Res Cardiol 91 (Suppl 1), 41–46 (1996). https://doi.org/10.1007/BF00795361
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DOI: https://doi.org/10.1007/BF00795361