Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: UMLS:C0019204 (hepatocellular carcinoma)
 71,386 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The role of glycosylation on the secretion and the stability of human corticosteroid binding globulin (CBG) was studied. Cells of the human hepatoma line were labeled by [35S]methionine in presence of or absence of tunicamycin (TM). Media or cells were harvested at 0, 3, 6, and 20 h after the addition of excess unlabeled methionine. Media and cell lysates were incubated with anti-CBG serum and immune complexes were precipitated with Staphylococcus aureus protein A (Pansorbin). Immunoprecipitates were analyzed by fluorography after sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Immunoprecipitation of T4-binding globulin (TBG) was also carried out with anti-TBG serum. Fluorographic analysis revealed three forms of CBG: CBG1, a glycosylated, mature, and secretory form with apparent mol wt of 70 K; CBG2, a glycosylated precursor which due to incomplete carbohydrate processing has an apparent mol wt of 54 K; and CBG3, a nonglycosylated form consisting of the 40 K core protein. In absence of TM, CBG1 was observed in media and CBG2 was detected in cell lysates. The proportion of CBG1 increased during the chase, whereas that of CBG2 decreased, indicating that CBG was secreted after processing of the oligosaccharides on CBG2. In presence of TM, CBG3 was found both in media and cell lysates. The sum of CBG3 in the medium and the cell lysate decreased during the chase, whereas that of CBG1 and CBG2 remained unchanged. Similar to CBG, TBG1 (mature form, 60 K) and TBG2 (partially processed glycosylated form, 54 K) were observed in media and cell lysates, respectively, in absence of TM. However, TBG3 (nonglycosylated, 44 K) was not detected in medium. These results indicate that glycosylation is not a key factor for the secretion of CBG but is important for its stability. On the other hand the glycosylation is indispensable for the secretion of TBG.
 ...
PMID:Studies on the role of glycosylation for human corticosteroid-binding globulin: comparison with that for thyroxine-binding globulin. 250 69

T4-binding globulin (TBG), the principal carrier of thyroid hormone in serum, is a glycoprotein containing 20% carbohydrate. The importance of the carbohydrate moiety has been previously studied by enzymatic deglycosylation, which showed that deglycosylated TBG retains its original immunological an T4-binding properties. However, the structure and properties of TBG before glycosylation and the steps involved in carbohydrate addition have not been explored. In the present report, we used a human hepatoma cell line (Hep G2) which synthesizes and secretes TBG into the medium. This TBG binds T4 and possesses immunoreactivity and microheterogeneity identical to those of native TBG (nTBG) from serum. Cells were pulsed with [35S]methionine, [3H]mannose, and [3H]glucosamine in the absence or presence of 5 micrograms tunicamycin/ml medium. Materials from cells and media were immunoprecipitated with antibodies specific for nTBG and denatured TBG molecule. They were then analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Cells incubated with [35S]methionine contained two forms of labeled TBG, with apparent mol wt of 60K (TBG1) and 54K (TBG2). Medium contained only the TBG1 form, which is identical to nTBG in serum. In contrast, in the presence of tunicamycin, the predominant intracellular form of TBG had an apparent mol wt of 44K (TBG3). At no time was this material detected in the medium. [3H]Mannose and [3H]glucosamine labeled both TBG1 and TBG2, but not TBG3. TBG1 and TBG2 reacted with anti-nTBG serum, whereas TBG3 reacted only with anti-dentured TBG serum, specific for the unfolded TBG molecule. Intracellular TBG was rich (80-90%) in high mannose (seven to nine mannose residues) oligosaccharides and was relatively poor (10-20%) in complex-type species, resistant to endoglycosidase H. These results indicate that 1) the precursor nonglycosylated 44K TBG3 is glycosylated to produce TBG2 (54K) and TBG1 (60K); 2) TBG2 contains oligosaccharides rich in mannose and appears to be a major intracellular intermediate in the synthesis of TBG1; 3) only the endoglycosidase H-resistant TBG1 is secreted; and 4) prior glycosylation of TBG appears to be required for the molecule to assume its tertiary structure and, ultimately, for its secretion. However, once the peptide chain is folded, removal of the carbohydrate moieties does not alter the tertiary structure.
 ...
PMID:The role of glycosylation in the molecular conformation and secretion of thyroxine-binding globulin. 308 30