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Endocrinology, Vol 134, 702-708, Copyright © 1994 by Endocrine Society

ARTICLES

The augmentation of insulin-like growth factor-I messenger ribonucleic acid in cultured rat hepatocytes: activation of protein kinase-A and -C is necessary, but not sufficient

Z Kachra, CR Yang and BI Posner
Polypeptide Hormone Laboratory, Royal Victoria Hospital, Montreal, Quebec, Canada.

In previous studies it was shown that bovine GH (bGH) and glucagon, when individually added to primary rat hepatocyte cultures, modestly stimulated IGF-I mRNA levels 1.8- to 2.5-fold, but when combined, synergized to stimulate IGF-I mRNA levels by 10- to 12-fold. In the present study we have explored further the mechanism of this effect in primary rat hepatocyte cultures. Like glucagon, the addition of 3- isobutyl-1-methylxanthine (100 microM) or (Bu)2cAMP (150 microM) augmented IGF-I mRNA levels 1.8- to 2.0-fold, but when combined with bGH (50 ng/ml), they augmented levels up to 12-fold. The half-life of IGF-I mRNA, determined by incubating hepatocytes with actinomycin-D was 12 h. Although bGH did not affect the decay rate, glucagon (100 ng/ml) or (Bu)2cAMP (100 microM) reduced the rate of loss by about 70%. 4 beta- Phorbol 12 beta-myristate 13 alpha-acetate minimally stimulated IGF-I mRNA levels 1.2- to 1.4-fold, but displayed no synergism when added with bGH, glucagon, or (Bu)2cAMP. The stimulatory effect of bGH plus glucagon was inhibited 80% after preincubation with 4 beta-phorbol 12 beta-myristate 13 alpha-acetate (10 microM) for 24 h. The addition of staurosporine, sphingosine, or H-7 [1-(5-isoquinolinyl sulfonyl)2- methyl piperazine] inhibited the stimulatory effect of bGH plus glucagon on hepatocyte IGF-I mRNA by 80%, 90%, and 85%, respectively. Preincubation with cycloheximide (10 micrograms/ml) blocked the synergistic effect of bGH plus either glucagon or (Bu)2cAMP by 65-80%. The effect of glucagon, mediated via the activation of adenylate cyclase, involves in part the posttranscriptional stabilization of IGF- I mRNA levels. The effect of GH, mediated in part by the activation of protein kinase-C, appears to be at the level of transcription. The synergistic augmentation of hepatocyte IGF-I mRNA levels by GH and glucagon involves the activation of PKA and PKC, but also appears to require the synthesis of one or more protein(s).


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J.-G. Scharf, T. G. Unterman, and T. Kietzmann
Oxygen-Dependent Modulation of Insulin-Like Growth Factor Binding Protein Biosynthesis in Primary Cultures of Rat Hepatocytes
Endocrinology, December 1, 2005; 146(12): 5433 - 5443.
[Abstract] [Full Text] [PDF]


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Copyright © 1994 by The Endocrine Society