Modulation of cystic fibrosis transmembrane conductance regulator gene - expression by elevation of intracellular cyclic AMP.
Cystic fibrosis (CF) is caused by mutations of the cystic fibrosis transmembrane conductance regulator (CFTR) gene. Its product is a cyclic AMP-dependent Cl- channel, that is defective in CF. Since cAMP regulates the expression of many genes and since the 5'-flanking region of the CFTR gene contains cAMP response elements, we hypothesized that intracellular cAMP might modulate not only the cAMP-dependent Cl- channel CFTR, but also CFTR gene expression in epithelial cells. To accomplish this, we investigated Cl- secretion and CFTR-mRNA levels in HT-29 and T84 colon carcinoma epithelial cells before and after exposure to forskolin and 8-bromo-cAMP for 12 hr. While resting T84 cells increased Cl- secretion in response to forskolin strongly and immediately, HT-29 cells did not, although both cell lines showed highly increased Cl- efflux in response to A23187, a calcium ionophore. Interestingly, prolonged exposure to forskolin (12 hr) induced a clear decrease of CFTR-mRNA levels in T84 cells, but an increase of CFTR-mRNA levels in HT-29 cells, thus demonstrating different behaviour of CFTR gene regulation in different epithelial cells in response to intracellular cAMP. These results suggest that cells with an effective cAMP-dependent Cl- channel (CFTR) respond to prolonged stimulation of this channel with down-regulation of CFTR gene expression, while cells with no effective cAMP-dependent Cl--secretion respond with an up-regulation of CFTR gene expression.
Bargon
J
J
Department of Internal Medicine II, Division of Pneumology, University Hospital Frankfurt, Theodor Stern Kai 7, D-60590 Frankfurt, Germany. bargon@t-online.de
Loitsch
S
S
Dauletbaev
N
N
von Mallinckrodt
C
C
Buhl
R
R
D015124:8-Bromo Cyclic Adenosine Monophosphate / Q000494:pharmacology; D001692:Biological Transport / Q000187:drug effects / Q000502:physiology; D002712:Chlorides / Q000378:metabolism; D005576:Colforsin / Q000494:pharmacology; D000242:Cyclic AMP / Q000378:metabolism*; D019005:Cystic Fibrosis Transmembrane Conductance Regulator / Q000032:analysis / Q000235:genetics*; D005786:Gene Expression Regulation / Q000187:drug effects / Q000502:physiology*; D019073:HT29 Cells / Q000737:chemistry / Q000502:physiology; D006801:Humans; D012333:RNA, Messenger / Q000032:analysis
C505032:CFTR protein, human; D002712:Chlorides; D012333:RNA, Messenger; D019005:Cystic Fibrosis Transmembrane Conductance Regulator; D005576:Colforsin; D015124:8-Bromo Cyclic Adenosine Monophosphate; D000242:Cyclic AMP