Dexamethasone stimulates transcription of the insulin-like growth factor-binding protein-1 gene in H4-II-E rat hepatoma cells.
Binding proteins for the insulin-like growth factors (IGFBP) are important modulators of the biological actions of IGF-I and IGF-II. Concentrations of one of these proteins, IGFBP-1, in human plasma and IGFBP-1 mRNA in rat liver are markedly altered in diabetes and fasting. We now examine the regulation of IGFBP-1 and IGFBP-I mRNA in H4-II-E cells, a rat cell line derived from the minimal deviation H35 Reuber hepatoma previously reported to synthesize IGFBP-1 as its predominant IGF-binding protein. Confluent H4-II-E cells in serum-free medium were incubated with different hormones for 48 h, and the conditioned medium was analyzed by ligand blotting. Dexamethasone (10(-6) M) increased levels of 30-kDa IGFBP-1 approximately 10-fold; stimulation was half-maximal at 6 x 10(-9) M dexamethasone. No stimulation was seen with progesterone, testosterone, IGF-I, or rat GH, whereas insulin gave a small inhibition. Immunoblot analysis using a monoclonal antibody to human IGFBP-1 confirmed that the 30-kDa IGFBP induced by dexamethasone was IGFBP-1. IGFBP-1 mRNA was increased to a similar extent (7-fold), as determined by Northern blot hybridization using human or rat IGFBP-1 cDNA probes. The stimulation of IGFBP-1 mRNA was observed within 3 h after the addition of dexamethasone; IGFBP-1 in the medium increased more slowly. After withdrawal of dexamethasone from stimulated cells, IGFBP-1 mRNA decreased by 80% after 48 h; IGFBP-1 decreased more slowly. The increased abundance of IGFBP-1 mRNA in dexamethasone-treated cells primarily reflected increased transcription rather than increased mRNA stability.(ABSTRACT TRUNCATED AT 250 WORDS)
Orlowski
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CC
Growth and Development Section, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland 20892.
Ooi
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GT
Rechler
M M
MM
D000818:Animals; D002352:Carrier Proteins / Q000235:genetics*; D015342:DNA Probes; D003907:Dexamethasone / Q000494:pharmacology*; D004591:Electrophoresis, Polyacrylamide Gel; D005786:Gene Expression Regulation / Q000187:drug effects*; D015151:Immunoblotting; D007328:Insulin / Q000494:pharmacology; D018969:Insulin-Like Growth Factor Binding Proteins; D008114:Liver Neoplasms, Experimental / Q000378:metabolism*; D009693:Nucleic Acid Hybridization; D012333:RNA, Messenger / Q000096:biosynthesis; D051381:Rats; D014158:Transcription, Genetic / Q000187:drug effects*; D014407:Tumor Cells, Cultured
D002352:Carrier Proteins; D015342:DNA Probes; D007328:Insulin; D018969:Insulin-Like Growth Factor Binding Proteins; D012333:RNA, Messenger; D003907:Dexamethasone