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At least 19 recordsLinked to original sources
PubMed1989

Transcortin biosynthesis and intracellular distribution of rat liver polyribosomes synthesizing transcortin.

Transcortin biosynthesis in rat has been examined using liver slices technique. The incorporation of 14C-labeled amino acids into the anti-transcortin-precipitable material of liver slices has been measured and compared with that of serum transcortin. It was shown that liver synthesized transcortin with an apparent mol. wt of 66 kDa on SDS-electrophoresis which co-migrated with authentic rat serum transcortin. In order to determine an intracellular distribution of transcortin synthesizing polyribosomes, the binding character of [125J]anti-transcortin-IgG to free and membrane-bound rat liver polyribosomes has been studied. It was shown that after incubation of [125J]anti-transcortin-IgG with liver membrane-bound polyribosomes, the radioactivity was associated with the discrete polyribosome fraction in heavy polyribosome region. In similar experiments the radioactivity of [125J]anti-transcortin-IgG bound to the free polyribosomes was distributed throughout the polyribosome region. The results of our experiments obviously demonstrated that serum transcortin was synthesized exclusively on membrane-bound polyribosomes of rat liver; free polyribosomes were devoid of detectable antigenic material able to bind antibodies to transcortin.

Animals↗
PubMed1991

Transcortin in rat kidney: subcellular distribution of transcortin-synthesizing polyribosomes.

The [3H]corticosterone-transcortin complexes from kidney cytosol show elution positions on DEAE-cellulose identical to serum transcortin. The incorporation of 14C-labeled amino acids into anti-transcortin-precipitable material of kidney slices has been measured and compared with that of serum transcortin. It was established that kidney synthesized transcortin with an apparent molecular weight of 66 kDa on SDS-electrophoresis which resembles serum corticosteroid-binding globulin. Studies on the binding of [125I]anti-transcortin-IgG to membrane-bound rat kidney polyribosomes revealed an association of [125I]anti-transcortin-IgG with a discrete polyribosome fraction in the heavy polyribosome region; free polyribosomes were devoid of antigenic material able to bind antibodies to transcortin.

Animals↗
PubMed1991

On the functional form of transcortin-recognizing subunit of transcortin membrane receptor.

Complex formation between transcortin and the 20 kDa sialoglycoprotein from the plasma membrane of human decidual endometrium (presumably a transcortin-recognizing subunit of transcortin membrane receptor) was studied using cross-linking reagents. The action of 1,5-difluoro-2,4-dinitrobenzene (DFDNB) on a solution of 125I-labelled 20 kDa sialoglycoprotein and unlabelled transcortin resulted in the formation of two 125I-containing containing species that corresponded to covalently linked complexes of one transcortin molecule and either 2 or 4 molecules of the labeled membrane sialoglycoprotein. Only the latter complex was observed when the endometrium membranes were incubated with [125I]transcortin and treated with DFDNB. This suggests that the functional form of transcortin-recognizing subunit of the membrane receptor is a tetramer.

Cell Membrane↗
PubMed1980

Unexplained high transcortin levels in patients with various hematological disorders and in the relatives: a connection between these high transcortin levels and HLA antigen B12.

Forty-one our of 141 patients with various hematological disorders had serum transcortin values more than 2 sDs above the normal mean (relative risk vs. controls, 10.78). Their relatives also had a higher incidence of unusually high transcortin values. The serum levels of steroid-binding beta-globulin were normal in these patients as well as in their relatives, making an increase in estrogenic impregnation as the cause of the high transcortin levels most improbable. Other known causes of increased transcortin levels could also be excluded. Such unusually high transcortin levels are 4.74 times more frequent in subjects carrying an HLA antigen B12 than in a control group [P (corrected) less than 0.006]. However, the HLA antigen B12 and hematological disorders were independently associated with high transcortin levels.

Adolescent↗
PubMed1980

Association of aberrant transcortin levels with HLA antigens of the B and C loci: high transcortin levels are frequently found in patients with lymphatic leukemia, hairy cell leukemia, or non-Hodgkin lymphoma.

HLA antigen B12 is in linkage disequilibrium with HLA antigen Cw5. In some way this particular haplotype seems to be associated with a mechanism increasing serum transcortin levels. As shown before, the latter mechanism does not involve elevated estrogen levels or a generalized increase in glycoprotein synthesis. Similar high transcortin levels (more than 2 SDs above the mean) are found frequently in patients with lymphatic leukemia, hairy cell leukemia, or non-Hodgkin lymphoma, as well as in the siblings of these patients. HLA antigen Bw35 is in linkage disequilibrium with HLA antigen Cw4. Transcortin levels in patients with this combination of HLA antigens are significantly lower than in patients who do not carry these two antigens. Relatives of subjects with very low transcortin levels often have the same low levels. These findings together with recent data in the literature suggest that a cluster of genes regulating certain aspects of glucocorticoid metabolism is located in the vicinity of HLA locus B and C.

Adolescent↗
PubMed1982

Transcortin: a corticosteroid-binding protein of plasma-XIV. Effects of time of equilibration of serum with cortisol on transcortin determinations by gel filtration.

The results of determination of plasma transcortin levels by gel filtration are subject to assay conditions such as duration of incubation and the amount of cortisol added. We investigated the cause for the dependency of results on assay conditions by incubating samples over prolonged periods of time. Transcortin concentration and the rate of dissociation of the cortisol-transcortin complex remained constant over many weeks of storage at 4 degree C, while irreversible binding to unidentified macromolecules increased continuously. Irreversible binding occurs faster at 37 degrees C than at 4 degrees C. In addition, with time, an ether-extractable, less polar metabolite of cortisol appears in the serum. The data suggest that a highly reactive metabolite of cortisol enters into covalent binding with macromolecules during prolonged incubations.

Adult↗
PubMed1989

Study of the transcortin binding to human endometrium plasma membrane.

Transcortin complexed with progesterone was shown to bind specifically to the plasma membrane of human decidual endometrium. The binding reaction was characterized by a high affinity (an apparent Kd value was (1.0 +/- 0.2).10(-10) mol/l) and high selectivity: such human serum proteins as albumin, orosomucoid, transferrin, thyroxine-binding globulin and sex hormone-binding globulin did not compete with transcortin for the membrane binding sites. Transcortin binding to the membrane was steroid-dependent: transcortin-cortisol complex bound to the membranes substantially more weakly than transcortin-progesterone, and specific binding of transcortin devoid of steroid was not detected. Using a radioimmunoassay, we have measured the concentration of endogenous transcortin in highly purified membrane preparations solubilized with sodium cholate. It was found that an extensive washing of decidual strips with a physiological buffer prior to the membrane isolation resulted in a decrease of the endogenous transcortin level along with an increase of the specific membrane binding of exogenous 125I-labeled transcortin. Affinity chromatography on immobilized transcortin was used to isolate transcortin-binding components from 125I-labeled, cholate-solubilized plasma membrane of decidual endometrium. Along with lipid components, the structure of which was not investigated, a 125I-labeled transcortin-binding sialoglycoprotein with a minimal Mr of 20.0 +/- 1.5 kDa and a pI of approx. 3.3 was detected. In the presence of transcortin, this sialoglycoprotein could be precipitated with a monospecific antitranscortin antiserum. Using hydroxylapatite as a separating agent, the interaction of transcortin and the membrane sialoglycoprotein in model systems containing the two proteins and various steroid hormones was studied. It was found that the membrane sialoglycoprotein displayed a higher affinity for transcortin-progesterone than for transcortin-cortisol (the Kd values were, respectively, 2.10(-11) and 7.10(-11) mol/l) and it did not bind transcortin complexed with testosterone.

Blood Proteins↗
PubMed1981

Plasma clearance and organ distribution of native and desialylated rat and human transcortin: species specificity.

Plasma clearance of intact and desialylated rat and human transcortin after iv injection into rats and hamsters has been investigated. Intact rat transcortin was shown to have an approximately 5-fold longer half-life in the rat circulation than human transcortin. Removal of sialic acid residues resulted in a reduction of the half-life of rat transcortin from 4 h to 90 sec. This rapid clearance could be blocked by simultaneous injection of asialofetuin, but the clearance of intact rat transcortin was unaffected by asialofetuin. Five rat organs (pancreas, uterus, kidney, liver, and psoas muscle) were sampled at 30 and 60 min after injection of iodinated rat or human transcortin and examined for their intact transcortin levels relative to those of plasma and [14C]sucrose distribution volumes. With the exception of the liver, the organs had lower tissue:plasma ratios of [125I]iodo-transcortin than did [14C]sucrose. Liver was found to accumulate 3--8 times more human [125I]iodo-transcortin than rat [125I]iodo-transcortin, suggesting that this organ plays a greater role in the degradation and plasma clearance of human transcortin. When injected into hamsters, rat and human transcortin both had relatively long half-lives (5.8 and 6.8 h, respectively), which were dramatically shortened when sialic acid was removed. Our results suggest that the differences observed in the half-lives of these two species of transcortin in the rat are most likely due to differences in the metabolism of these two transcortins by the endogenous neuraminidase(s).

Animals↗
PubMed1995

Organization of the transcortin-binding domain on placental plasma membranes.

Complex formation between transcortin (corticosteroid-binding globulin) and 20 kDa sialoglycoprotein from human syncytiotrophoblast plasma membranes (presumably a transcortin-recognizing subunit of the transcortin membrane receptor) was studied using FPLC and cross-linking with bifunctional reagents. The action of 1,5-difluoro-2,4-dinitrobenzene (DFDNB) on a solution of the purified 20 kDa sialoglycoprotein and transcortin resulted in formation of covalently linked complexes of 95 kDa and 140 kDa consisting of one transcortin molecule and either two or four molecules of the membrane sialoglycoprotein (the molecular mass of transcortin is 55 kDa). Additionally, cross-linking resulted in the appearance of a 43 kDa species which is the cross-linked dimer of the membrane protein. The dimer was also observed during chromatography on a Superose 12 column in the absence of DFDNB treatment. Treatment of intact syncytiotrophoblast membranes with DFDNB resulted in isolation of the transcortin binding protein dimer as the major portion of total pool of the protein. Formation of the transcortin complexes with two and four molecules of the membrane protein was also observed when the membranes were incubated with 125I-labeled transcortin and treated with DFDNB, but formation of the latter complexes predominated. The results obtained suggest that the recognizing and binding domain for transcortin in placental membranes is organized as dimers consisting of non-covalently linked sialoglycoprotein monomers of a 20 kDa each and that transcortin has two sites for interaction with this dimer. Apparently, binding of two dimers results in the formation of the functional form of the transcortin-receptor complex. The possible biological role of such a complex is discussed.

Binding Sites↗
PubMed1985

Human transcortin synthesis by a cell-free translation of hepatic mRNA.

To evaluate the site of synthesis and to characterize the translated transcortin, poly (A)-containing RNA (mRNA) from human liver was translated in a cell-free system derived from rabbit reticulocyte lysate. The in vitro synthesized product was identified as transcortin by immuno-precipitation with its specific antiserum. This translated transcortin could be displaced from the antibody by unlabeled purified transcortin obtained from plasma. Furthermore, when the translation mixture was applied to a cortisol-Sepharose column, the translated transcortin was bound to the matrix in a specific manner, indicating that this product binds to cortisol. The molecular weight of the translated transcortin was estimated to be 45,700 by its mobility in sodium dodecyl sulfate polyacrylamide gel electrophoresis, while that of plasma transcortin was 53,800. The difference in molecular weight between the translated transcortin and plasma transcortin was probably due to the presence of pre-sequence (signal peptide) in addition to the absence of carbohydrate moiety in the former. In conclusion, human liver mRNA directed the synthesis of transcortin, and the translated transcortin binds to cortisol in spite of the absence of carbohydrate moiety.

Animals↗
PubMed1983

Radioimmunoassay of human transcortin.

A specific, sensitive and simple radioimmunoassay (RIA) system for human transcortin was developed. A highly purified transcortin was prepared from pooled human serum by the following four successive steps; ammonium sulfate fractionation, cortisol-Sepharose column chromatography, Ultragel AcAA column chromatography and hydroxylapatite column chromatography. Anti-transcortin antibody was raised by immunizing rabbits. The RIA employing 125I-labeled transcortin preparation and polyethylene glycol solution for separation of free and bound-form was sensitive to transcortin in concentrations as low as 10 ng/ml. This RIA was reliable in the tests of dilution, reproducibility and recovery. The presence of cortisol does not interfere with the assay. Also a test of cross reactivity revealed that the system was not influenced by human serum albumin in a concentration 10,000 times that of transcortin. The transcortin concentrations determined by the RIA (Y) and those by the conventional steroid-binding assay (X) revealed a good correlation (Y = 1.01 X + 6.25) in normal serum, and the immunoreactivity and steroid binding activity revealed a good correlation in heat and acid-inactivated transcortin. With some total cortisol concentrations given, the transcortin concentrations were inversely correlated with protein-unbound cortisol concentrations. The present assay is useful not only for biochemical research but also for clinical studies, in which the determination of transcortin makes it possible to evaluate the concentration of protein-unbound cortisol which is the physiologically active fraction in serum.

Adult↗
PubMed1984

[Transcortin concentrations in the plasma of normal persons and patients with kidney and liver diseases].

The purpose of the study was to assess the influence of chronic kidney and liver diseases on the transcortin concentrations in plasma. The mean (+/- SD) plasma concentration of transcortin was 45.0 +/- 6.7 mg/l in women not taking oral contraceptive steroids and 41.2 +/- 6.7 mg/l in healthy male volunteers. Patients with the nephrotic syndrome had low transcortin concentrations (females: 20.9 +/- 8.5 mg/l; males: 26.0 +/- 6.0 mg/l). Abnormally low concentrations were measured in females treated for endstage renal disease with chronic ambulant peritoneal dialysis (CAPD) (30.8 +/- 7.5 mg/l). Patients on hemodialysis or with a functioning renal allograft had normal transcortin concentrations in plasma. Females suffering from a primary biliary cirrhosis had normal transcortin concentrations and male patients with an alcoholic cirrhosis had abnormally low mean transcortin concentrations in plasma (32.6 +/- 7.4 mg/l). The transcortin concentrations in patients with a Gilbert syndrome were normal. Among patients with a kidney or liver disease, the large variability of the transcortin concentration in plasma indicates that the knowledge of the transcortin concentration or the unbound steroid concentration in plasma is mandatory for the interpretation of total glucocorticoid concentrations in plasma.

Adult↗
PubMed1988

Evidence for the involvement of the transcortin carbohydrate moiety in the glycoprotein interaction with the plasma membrane of human placental syncytiotrophoblast.

We have studied the interaction of human transcortin and the pregnancy-associated transcortin variant with the microvesicular membrane fraction derived from the human placental syncytiotrophoblast. Two classes of specific binding sites for these glycoproteins were found in this membrane preparation. One of these displays a relatively high binding capacity, Bmax = 140 +/- 60 fmol transcortin per mg membrane protein, and a significantly higher affinity for transcortin, Kd = (1.6 +/- 0.6).10(-10) mol/l, than for the pregnancy-associated variant, Kd = (4.5 +/- 1.2).10(-9) mol/l. On the contrary, another class of the binding sites, occurring in the membranes at a far lower concentration: Bmax = 3.0 +/- 2.2 fmol transcortin per mg membrane protein, shows a higher affinity for the pregnancy-associated transcortin variant, Kd = (3.3 +/- 2.0).10(-12) mol/l, than for normal transcortin, Kd = (2.5 +/- 0.7).10(-11) mol/l. Since the pregnancy-associated variant differs from normal transcortin with respect to its carbohydrate structures only (Avvakumov, G.V. and Strel'chyonok, O.A. (1987) Biochim. Biophys. Acta 925, 11-16), the results of the present work suggest that the transcortin carbohydrates are directly involved in the specific interaction of this serum hormone-binding globulin with the plasma membrane of the placental syncytiotrophoblast.

Binding, Competitive↗