Expression of hepatic insulin-like growth factor-I and insulin-like growth factor-binding protein-1 genes is transcriptionally regulated in streptozotocin-diabetic rats.
Insulin-like growth factor-I (IGF-I) and IGF-binding protein-1 (BP-1) are critical cell regulators, with regulation and action in endocrine, paracrine, and autocrine modes. Although IGF-I and BP-1 are thought to be modulated mainly at the level of synthesis, underlying molecular mechanisms are poorly understood. To examine regulation by insulin, we used run-on assays to measure IGF-I and BP-1 gene transcription rates in nuclei isolated from the livers of normal and diabetic rats. Streptozotocin (STZ)-treated rats exhibited 20-25% weight loss, a 2.5- to 3-fold increase in serum glucose, and a 50-60% fall in circulating IGF-I levels (all P less than 0.001). Diabetic animals also had a 45% reduction in hepatic IGF-I mRNA and over 400% increases in BP-1 mRNA (both P less than 0.005); all parameters were restored toward normal after treatment with insulin. Metabolically responsive IGF-I gene transcription was evaluated effectively with a 3.2-kilobase BglII/EcoRI genomic probe located down-stream from all initiation sites in exon 1, while BP-1 gene transcription was studied with a cDNA probe. Animals treated with 144 mg/kg STZ exhibited 50-97% decreases in IGF-I gene transcription (P less than 0.05), while insulin treatment raised IGF-I gene transcription to control levels (P less than 0.02). IGF-I gene transcription appeared to be more sensitive to metabolic status than IGF-I mRNA levels, resulting in a modest correlation between transcription rates and mRNA levels (r = 0.68; P less than 0.001). In contrast, changes in BP-1 mRNA and gene transcription appeared to be exquisitely sensitive to metabolic status.(ABSTRACT TRUNCATED AT 250 WORDS)
Pao
C I
CI
Department of Medicine, Emory University School of Medicine, Atlanta, Georgia 30303.
Farmer
P K
PK
Begovic
S
S
Goldstein
S
S
Wu
G J
GJ
Phillips
L S
LS
D000818:Animals; D001483:Base Sequence; D001786:Blood Glucose / Q000032:analysis; D002352:Carrier Proteins / Q000096:biosynthesis* / Q000235:genetics; D003921:Diabetes Mellitus, Experimental / Q000188:drug therapy / Q000235:genetics / Q000378:metabolism*; D005786:Gene Expression Regulation; D007328:Insulin / Q000494:pharmacology / Q000627:therapeutic use; D018970:Insulin-Like Growth Factor Binding Protein 1; D007334:Insulin-Like Growth Factor I / Q000096:biosynthesis* / Q000235:genetics; D008099:Liver / Q000378:metabolism*; D008297:Male; D008969:Molecular Sequence Data; D012333:RNA, Messenger / Q000096:biosynthesis; D051381:Rats; D011919:Rats, Inbred Strains; D012091:Repetitive Sequences, Nucleic Acid; D013311:Streptozocin; D014158:Transcription, Genetic; D015431:Weight Loss
D001786:Blood Glucose; D002352:Carrier Proteins; D007328:Insulin; D018970:Insulin-Like Growth Factor Binding Protein 1; D012333:RNA, Messenger; D013311:Streptozocin; D007334:Insulin-Like Growth Factor I