Differential regulation of IGF-binding protein gene expression by cAMP in rat C6 glioma cells.
We previously reported that cAMP inhibits autocrine IGF-I gene expression in rat C6 glioma cells. In this study we examined the influence of cAMP on IGF-binding protein gene expression in C6 cells. cAMP potently inhibited IGF-binding protein-3 mRNA and, to a lesser extent, IGF-binding protein-4 mRNA and transiently stimulated IGF-binding protein-5 mRNA. The changes in secreted IGF-binding proteins whose molecular weights were consistent with IGF-binding protein-3 and -5 correlated with those of mRNA levels. cAMP decreased the IGF-binding protein-3 mRNA half-life, but did not alter IGF-binding protein-4 and -5 mRNA half-lives. An IGF-binding protein-5 promoter/luciferase fusion construct containing 888 bp of 5'-flanking sequence and the first 114 bp of exon 1 sequence was stimulated by cAMP after 24 h by approximately 2-fold in transient transfection assays. 5'- or 3'-deletion to -33 or +10 (the transcription start site was designated as +1), respectively, did not alter the increase caused by cAMP. Site-directed mutagenesis of the region from -14 to -5 led to a loss of the ability of the IGF-binding protein-5 promoter to respond to cAMP. H89, a cell-permeable protein kinase A inhibitor, did not alter the regulation of IGF-binding protein mRNAs in response to cAMP.
Wang
L
L
Department of Biochemistry, University of Texas Health Science Center, San Antonio, Texas 78229-3900, USA.
Ma
X
X
Yeh
L C
LC
Adamo
M L
ML
D000818:Animals; D001932:Brain Neoplasms / Q000235:genetics*; D002460:Cell Line; D000242:Cyclic AMP / Q000031:analogs & derivatives / Q000494:pharmacology / Q000502:physiology*; D003513:Cycloheximide / Q000494:pharmacology; D015870:Gene Expression / Q000187:drug effects; D015972:Gene Expression Regulation, Neoplastic; D005910:Glioma / Q000235:genetics*; D018972:Insulin-Like Growth Factor Binding Protein 3 / Q000235:genetics; D018975:Insulin-Like Growth Factor Binding Protein 5 / Q000235:genetics; D018969:Insulin-Like Growth Factor Binding Proteins / Q000235:genetics*; D011401:Promoter Regions, Genetic / Q000187:drug effects / Q000502:physiology; D011500:Protein Synthesis Inhibitors / Q000494:pharmacology; D020871:RNA Stability / Q000187:drug effects; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D013873:Thionucleotides / Q000494:pharmacology
D018972:Insulin-Like Growth Factor Binding Protein 3; D018975:Insulin-Like Growth Factor Binding Protein 5; D018969:Insulin-Like Growth Factor Binding Proteins; D011500:Protein Synthesis Inhibitors; D012333:RNA, Messenger; D013873:Thionucleotides; C015929:8-((4-chlorophenyl)thio)cyclic-3',5'-AMP; D003513:Cycloheximide; D000242:Cyclic AMP