The regulation of insulin-like growth factor-binding protein 1 messenger ribonucleic acid in cultured rat hepatocytes: the roles of glucagon and growth hormone.

Abstract

In previous studies it was shown that bovine GH (bGH) suppressed and glucagon stimulated the level of 24- and 30- to 34-kilodalton insulin-like growth factor-binding proteins (IGFBPs) in the media of cultured rat hepatocytes. In the present study we have evaluated the regulation of IGFBP-1 gene expression in primary rat hepatocyte cultures. Glucagon produced a dose-dependent stimulation of hepatocyte IGFBP-1 messenger RNA (mRNA), attaining levels 2- to 6-fold greater than control at a glucagon concentration of 100 ng/ml. GH inhibited the accumulation of IGFBP-1 mRNA in a dose-dependent manner producing, 40-70% inhibition at 50 ng/ml. The effect of glucagon was comparable to and additive with dexamethasone (1 microM). The addition of 3-isobutyl-1-methylxanthine (100 microM) and (Bu)2cAMP (100 microM) augmented IGFBP-1 mRNA levels 5- to 6-fold. 4 beta-Phorbol 12 beta-myristate 13 alpha-acetate (300 nM) was found to inhibit IGFBP-1 mRNA levels by 40-50%. The inhibitory effect of bGH on IGFBP-1 mRNA levels was abolished after preincubation with 4 beta-phorbol 12 beta-myristate 13 alpha-acetate (10 microM) for 24 h, whereas glucagon's stimulatory effect was unaffected. The addition of staurosporine (500 nM) and H-7 (1 mM) abolished the inhibitory effect of GH but also significantly inhibited the stimulatory effect of glucagon, a result consistent with these agents acting on both protein kinase C (PKC) and PKA. In the presence of 10 micrograms/ml cycloheximide, IGFBP-1 gene expression was superinduced by bGH, whereas the effect of glucagon was uninfluenced. Thus the inhibitory action of GH involves, in part, the activation of PKC. Glucagon's stimulatory effect seems to involve the activation of PKA. The inhibitory effect of bGH on IGFBP-1 gene expression may require the continuing synthesis of one or more labile protein(s).

Metabolic hormones regulate insulin-like growth factor binding protein-1 mRNA levels in primary cultured salmon hepatocytes; lack of inhibition by insulin

“…Glucagon increased IGFBP-1 mRNA levels and protein secretion at concentrations approximately 100-fold lower in primary rat hepatocytes (Denver & Nicoll 1994, Kachra et al 1994, and the responses to dexamethasone and GH occurred at physiological concentrations in the present study. Therefore, the present study suggests that glucagon may not regulate salmon liver IGFBP-1 production under normal physiological conditions.…”

“…Triiodothyronine (10 K7 M) did not significantly change IGFBP-1 mRNA levels in salmon hepatocytes. Triiodothyronine increases IGFBP-1 mRNA levels in mammalian hepatoma cell lines, but may decrease it in mammalian primary hepatocytes (Kachra et al 1994, Demori et al 1997. These and other divergent results on IGFBP-1 regulation in mammalian cell culture may be due to differences in culture conditions.…”

“…While insulin and glucocorticoids are thought to be the primary hormonal regulators of liver IGFBP-1 production, other anabolic and catabolic hormones also play roles. In general, growth hormone (GH) decreases and glucagon increases hepatocyte IGFBP-1 mRNA levels (Denver & Nicoll 1994, Kachra et al 1994, Thissen et al 1994. Cytokines directly induce IGFBP-1 (Lee et al 1997).…”

CCAAT/Enhancer-binding Protein δ Activates Insulin-like Growth Factor-I Gene Transcription in Osteoblasts

“…Hormones that activate cAMP have been shown to stimulate IGF-I gene expression in other tissues, including the liver (43)(44)(45). PGE 2 and dibutyryl cAMP both enhanced IGF-I synthesis in bone marrow macrophages, although both paradoxically produced a decline in steady-state levels of IGF-I mRNA (46).…”

Regulation of Hepatic Insulin-Like Growth Factor-Binding Protein-1 Gene Expression by Insulin: Central Role for Mammalian Target of Rapamycin Independent of Forkhead Box O Proteins

“…Previous work compared Northern blotting with dot blots and established that the latter were as quantitatively accurate in assessing IGFBP-1 mRNA levels (19,31). As in previous work, dot-blot analyses of 20 g total RNA were performed on Hybond-N nylon membranes (GE Healthcare Life Sciences, Baie d'Urfé, Québec, Canada) in a dot-blot manifold (Bio-Rad Laboratories, Inc., Hercules, CA), according to the manufacturer's protocol.…”