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Regulation of acute phase protein genes by hepatocyte-stimulating factors, monokines and glucocorticoids.
The synthesis of all the major acute phase plasma proteins is stimulated in rat hepatoma and primary cultures of hepatocytes by three, structurally and functionally distinct groups of hormones: 1) hepatocyte-stimulating factors (HSF) and interleukin-6 (IL-6); 2) interleukin-1 (IL-1) and tumor necrosis factor (TNF); and 3) glucocorticoids. Each plasma protein gene requires a specific combination of these 3 hormone types for maximal expression. One set of acute phase proteins, including alpha 2-macroglobulin, alpha 1-antichymotrypsin ( = contrapsin), cysteine protease inhibitor ( = thiostatin), alpha 1-antitrypsin, ceruloplasmin and fibrinogens are predominantly regulated by the keratinocyte-derived HSF-III/-II or IL-6, while a second set of proteins, including alpha 1-acid glycoprotein (AGP), haptoglobin and complement C3 are predominantly regulated by keratinocyte-derived HSF-I, IL-1 or TNF. In conjunction with the above peptide hormones, glucocorticoids synergistically enhance the stimulated expression of most, but not all, acute phase proteins. An exceptionally strong synergy between HSF (or IL-6), IL-1 and glucocorticoids is noted for the activation of the AGP gene. To elucidate the molecular mechanisms of regulation, we have identified the cis-acting genetic elements through which all these hormones control the transcriptional activity of the AGP gene. It appears that acute phase activates a specific nuclear binding protein in the rat liver that interacts with the peptide hormone responsive element located 5 kb upstream of the transcriptional start site.
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