Regulation of insulin-like growth factor I transcription by prostaglandin E2 in osteoblast cells.
Insulin-like growth factor I (IGF-I) is a widely expressed abundant autocrine and paracrine factor that regulates the proliferation and differentiation of a variety of cell types. Prostaglandin E2 (PGE2) is a potent stimulator of IGF-I synthesis in bone. We examined the regulation of IGF-I synthesis by PGE2 in osteoblast-enriched (Ob) cells from fetal rat calvaria. PGE2 treatment of Ob cells at 1 microM for 2 h resulted in a 5-fold increase in heterogeneous nuclear RNA levels, as measured by a reverse transcriptase-polymerase chain reaction assay, suggesting an increase in IGF-I gene transcription. RNase protection analysis was used to map the transcriptional start sites in the IGF-I gene that are used in Ob cells. Consistent with other extrahepatic tissues, initiation of transcription occurs primarily at three sites within the 5'-regions of exon 1 of the IGF-I gene. PGE2 treatment did not alter start site usage. The regions upstream of these transcriptional start sites were analyzed by transiently transfecting Ob cells with putative rat IGF-I promoter sequences ligated to a luciferase reporter gene. Constructs containing 1.4 kilobases of the 5'-regions regions of exons 1 and 2 had significant promoter activity. PGE2 treatment of transfected Ob cells increased luciferase activity 5-fold when a 1.4-kilobase exon 1 promoter fragment was tested. This increase in luciferase activity was time and dose dependent. Smaller regions of the exon 1 promoter sequence gave higher basal activity and were less responsive to PGE2. We conclude that regions involved in IGF-I regulation by PGE2 are contained within the IGF-I promoter.
Pash
J M
JM
Department of Research, Saint Francis Hospital and Medical Center, Hartford, Connecticut 06105.
Delany
A M
AM
Adamo
M L
ML
Roberts
C T
CT
LeRoith
D
D
Canalis
E
E
D000818:Animals; D001483:Base Sequence; D004247:DNA / Q000235:genetics; D015232:Dinoprostone / Q000494:pharmacology*; D004622:Embryo, Mammalian / Q000166:cytology; D005091:Exons; D007334:Insulin-Like Growth Factor I / Q000235:genetics*; D008156:Luciferases / Q000235:genetics; D008969:Molecular Sequence Data; D015345:Oligonucleotide Probes / Q000235:genetics; D010006:Osteoblasts / Q000187:drug effects / Q000502:physiology*; D016133:Polymerase Chain Reaction; D011401:Promoter Regions, Genetic; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D012886:Skull / Q000166:cytology / Q000196:embryology; D014158:Transcription, Genetic / Q000187:drug effects*
D015345:Oligonucleotide Probes; D012333:RNA, Messenger; D007334:Insulin-Like Growth Factor I; D004247:DNA; D008156:Luciferases; D015232:Dinoprostone