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Activity and secretion of sialyltransferase in primary monolayer cultures of rat hepatocytes cultured with and without dexamethasone



Activity and secretion of sialyltransferase in primary monolayer cultures of rat hepatocytes cultured with and without dexamethasone



Canadian Journal of Biochemistry & Cell Biology 64(2): 79-84



Monolayers of hepatocytes attached on collagen-coated dishes were cultured for 20-24 h and were found suitable to study the activity and secretion of CMP-N-acetylneuraminate:asialo-.alpha.1-acid glycoprotein sialyltransferase. A progressive increase of sialyltransferase activity in the culture medium was observed during incubation of the hepatocytes. After 24 h 34-48% of the total sialyltransferase activity of the hepatocyte incubation system was present in the medium. The enzyme activity present in the medium was soluble in nature and could not be stimulated by Triton X-100. The secretion of the enzyme was stimulated about twofold by dexamethasone. The activity of sialyltransferase in the hepatocytes was also increased by dexamethanasone. The Km of either hepatocyte or medium sialyltransferase for CMP-sialic acid was only slightly changed by dexamethasone, whereas the Vmax was increased about twofold. The secretoin of sialyltransferase could be inhibited partially by the anti-microtubular agent colchicine. The dexamethasone-induced increase of the sialyltransferase activity in cells and media could be eliminated by inclusin of .alpha.-amanitin in the culture media at 0 h. The inhibiting effect of .alpha.-amanitin was only partially expressed when the drug was added 4 h after the addition of dexamethasone to the media. The results suggest that isolated rat hepatocytes actively secrete sialyltransferase and that the increase in the sialyltransferase activity in cells and media owing to the synthetic glucocorticosteroid dexamethasone results from increased synthesis of the enzyme molecule. It is supposed that the intact rat the increased levels of the enzyme activity in serum observed in inflammation may originate from an induction of the synthesis of sialyltransferase in the hepatocytes of ra liver by the increased levels of circulating corticosteroids.

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Accession: 004666077

Download citation: RISBibTeXText

PMID: 3718701

DOI: 10.1139/o86-014


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