Down-regulation of the cyclin A promoter by transforming growth factor-beta1 is associated with a reduction in phosphorylated activating transcription factor-1 and cyclic AMP-responsive element-binding protein.
Transforming growth factor (TGF)-beta1 prevents cell cycle progression by inhibiting several regulators, including cyclin A. To study the mechanisms by which TGF-beta1 down-regulates cyclin A gene expression, we transfected reporter plasmids driven by the cyclin A promoter into mink lung epithelial cells in the absence and presence of TGF-beta1. The TGF-beta1-induced down-regulation of cyclin A promoter activity appeared to be mediated via the activating transcription factor (ATF) site, because mutation of this site abolished down-regulation. Surprisingly, although TGF-beta1 treatment for 24 h markedly decreased cyclin A promoter activity, it did not decrease the abundance of the ATF-binding proteins ATF-1 and cyclic AMP-responsive binding protein (CREB). However, we detected 90 and 78% reductions (by Western analysis) in phosphorylated CREB and ATF-1, respectively, in mink lung epithelial cells treated with TGF-beta1. TGF-beta1-induced down-regulation of cyclin A promoter activity was reversed by okadaic acid (a phosphatase inhibitor) and by cotransfection with plasmids expressing the cAMP-dependent protein kinase catalytic subunit or the simian virus small tumor antigen (Sm-t, an inhibitor of PP2A). These data indicate that TGF-beta1 may down-regulate cyclin A promoter activity by decreasing phosphorylation of CREB and ATF-1.
Yoshizumi
M
M
Cardiovascular Biology Laboratory, Harvard School of Public Health, Boston, Massachusetts 02115, USA.
Wang
H
H
Hsieh
C M
CM
Sibinga
N E
NE
Perrella
M A
MA
Lee
M E
ME
D051697:Activating Transcription Factor 1; D000818:Animals; D000952:Antigens, Polyomavirus Transforming / Q000378:metabolism; D002478:Cells, Cultured; D017362:Cyclic AMP Response Element-Binding Protein / Q000378:metabolism*; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism; D016213:Cyclins / Q000235:genetics*; D004268:DNA-Binding Proteins; D015536:Down-Regulation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D008168:Lung / Q000378:metabolism; D008907:Mink; D019319:Okadaic Acid / Q000494:pharmacology; D010766:Phosphorylation; D011401:Promoter Regions, Genetic; D014157:Transcription Factors / Q000378:metabolism*; D016212:Transforming Growth Factor beta / Q000494:pharmacology*
D051697:Activating Transcription Factor 1; D000952:Antigens, Polyomavirus Transforming; D017362:Cyclic AMP Response Element-Binding Protein; D016213:Cyclins; D004268:DNA-Binding Proteins; D004791:Enzyme Inhibitors; D014157:Transcription Factors; D016212:Transforming Growth Factor beta; D019319:Okadaic Acid; D017868:Cyclic AMP-Dependent Protein Kinases