Soluble Iodoproteins Research Articles

Depletion and reaccumulation of follicular thyroglobulin (TG) in guinea-pig thyroid gland after short- and long-term administration of thyrotropin (TSH).

The relationships among the content and composition of soluble iodoproteins in thyroid gland, the serum Tg concentration and the morphological structure of gland were investigated in guinea-pigs during short-term and long-term TSH administration (2 I.U. per day for 1 to 28 days). A significant decrease in the content of Tg in the gland (from 6.50 mg to 1.32 mg/100 mg tissue), disappearance of 12 S iodoprotein, hypertrophy and hyperplasia of the follicular cells were observed in guinea-pigs treated with TSH up to 7 days. Later on, after depletion of follicular colloid, reaccumulation of colloid in the preexisting and newformed follicles (a marked increase of Tg and 12 S protein) and partial involution of the structural changes occurred. The serum Tg concentration increased during the whole period of TSH treatment (mean values from 100 to 500 micrograms/l). A marked positive correlation between serum Tg concentration and thyroid weight was found. Serum T3 and T4 concentrations increased transiently with maximal values on the 1st day (T3, from 0.86 to 3.26 nmol/l, T4, from 44 to 138 nmol/l) and decreased thereafter. The results imply that different regulatory mechanisms exist which control thyroid hormone secretion and transfer of Tg from the gland into blood circulation. The serum Tg level is directly dependent on the total bulk of thyroid tissue, but is considerably less dependent on the structure of the gland. The reaccumulation of colloid (Tg) in thyroid follicles of guinea-pigs treated with TSH is a result of the reduction of the stimulatory effect of TSH on the process of Tg degradation during chronic hormone application. Several different factors may be responsible for the appearance of refractoriness or desensitization of the thyroid to prolonged exogenous TSH stimulation.

Thyroid function and thyrotropin levels in rabbits immunized to produce antibodies against thyroid hormones

Various parameters of thyroid function were studied in 27 rabbits, out of which 10 were immunized to produce antibodies against triiodothyronine (T 3), 9 against thyroxine (T 4) and 8 were normals. Estimations of T 3, T 4, Free T 4 (FT 4) and thyrotropin (TSH) in blood, qualitative and quantitative analysis of iodoamino acids in serum, protein bound iodine-131 (PB 131I), butanol extractable iodine-125 (BE 125I) and measurement of the disappearance rates of 125I-labelled T 3 and T 4 from plasma were done. In addition, glandular changes were also studied by measurement of 131I uptake, thyroid scanning and chromatographic analysis of hydrolysate of soluble iodoproteins. In T 3 immunized animals, levels of T 3 in serum increased by 38 to 125 times, levels of TSH also showed a significant rise (7.4 ± 1.2 vs 28 ± 9 ng/mL). Chromatographic analysis of iodoamino acids in serum as well as in the hydrolysate of the thyroid gland demonstrated a selective increase in synthesis of T 3. Rate of disappearance of T 3 from blood showed a significant decline. Thyroid glands in the immunized rabbits showed signs of hypertrophy and hyperplasia. Identical studies done in rabbits immunized to produce antibodies against T 4 showed a similar pattern though of variable degree. Our studies indicate that the thyroid glands of the immunized rabbits undergo marked alterations resulting in selective increase in the synthesis and secretion of the particular thyroid hormone against which they were immunized. They do so under the influence of increased levels of TSH.

Intrathyroidal thyroglobulin in streptozotocin-diabetic rats.

In order to elucidate whether or not the 'coupling defect' observed in thyroids from diabetic rats is due to a structural defect of intrathyroidal thyroglobulin (Tg), the sedimentation pattern and the stability of the thyroidal soluble iodoproteins were studied in control (C), food restricted (FR), diabetic (D) and insulin-treated diabetic (D+I) rats fed a low iodine diet either with (NID) or without (LID) iodide supplementation and labelled with 125I: acutely, 24 h prior to sacrifice and chronically, by feeding the corresponding diet labelled for 60 days. Diabetes resulted in a decrease of thyroidal weight, an increase of both thyroidal 127I content and concentration and decreased plasma TSH, irrespective of the diet. Insulin treatment reversed these alterations. Food restriction led to an intermediate situation between C and D. The iodoamino acid distribution in the acutely labelled thyroidal soluble iodoproteins showed a significant increase in the percent of organified 125I found as iodotyrosines (MIT and DIT) and a decrease of that found as iodothyronines (T3 and T4) both in D and FR. However, in the isotopically equilibrated groups, no differences were found except in LID-D where a slight increase in DIT and a decrease in T3 was found as compared to the corresponding control. The sedimentation patterns of both acutely and chronically labelled thyroidal soluble iodoproteins from all experimental groups displayed two peaks. The main one, corresponding to Tg, had a slightly lower sedimentation coefficient than the 19 S internal marker run in parallel, while the second one, relatively small, formed probably by dissociation of the main Tg peak, sedimented more slowly (12- 14 S).(ABSTRACT TRUNCATED AT 250 WORDS)

RETARDED BIOSYNTHESIS OF THYROGLOBULIN SUBUNITS AND THEIR POLYMERIZATION IN VITRO AFTER SUPPRESSION OF TSH SECRETION IN RATS BY CHRONIC ADMINISTRATION OF EXCESS THYROXINE IN THE FORM OF IODINATED CASEIN

ABSTRACT The effects of short- and long-term (from 3 days to 28 weeks) administration of excess thyroxine in the form of the iodinated casein "Protamone" (0.2%) to rats on the content of soluble thyroid iodoproteins and on biosynthesis and polymerization of thyroid proteins in vitro were investigated. The concentration of soluble iodoproteins significantly increased (40–80%) up to 2 weeks of treatment, and after that remained at the same level. 27S iodoprotein markedly increased during thyroxine treatment. The content of DNA in the gland and the thyroid weight were a little lower in the treated rats than in the control. The incorporation rate of [14C]leucine into soluble and microsome-bound proteins in vitro was markedly reduced in the treated animals (30–80 % of control). Thyroxine pre-treatment of rats induced retarded synthesis of thyroglobulin and its subunits in vitro. The inhibition of the synthesis of thyroid proteins in vitro and the incrrease in the soluble iodopritein content in the gland in vivo was not correlated with the duration of thyroxine treatment. The immobilization of pre-formed thyroglobulin in the follicle lumen for a long time period is probably an important factor in the enlarged conversion of thyroglobulin into 27S iodoprotein. In conclusion, the long-term suppression of endogenous TSH secretion by administration of thyroxine results in an accumulation of iodoproteins in the thyroid and a reduced rate of synthesis of iodoproteins; after 2 weeks a steady state is reached both with regard to iodoprotein accumulation and synthesis. Finally, the results obtained suggest that the thyroid-pituitary axis becomes adapted to chronic administration of excess thyroxine.

Isolation of desialylated and low-iodinated thyroglobulin in an experimental rat thyroid tumour.

ABSTRACT In an experimental rat thyroid tumour (Wollman line 1-1C2) thyroglobulin (TG) was isolated from soluble iodoproteins by ammonium sulphate fractionation and density gradient ultracentrifugation. The isolated TG was characterized by polyacrylamide gel electrophoresis, microimmunodiffusion, immunoelectrophoresis, analytical ultracentrifugation and by chemical determination of sialic acid and iodine content. Tumour thyroglobulin has a sedimentation coefficient of 17.7S, which is similar to that of enzymatically desialylated thyroglobulin (18.4S) in the normal rat; tumour TG shows a slower electrophoretic mobility than native TG and similar to rat desialylated TG. In double immunodiffusion tumour TG is shown to precipitate with an identity reaction with both native and desialylated rat TG; in immunoelectrophoresis it has a slower migration than native TG and is very close to that of enzymatically desialylated TG. Tumour TG has an iodine content of 0.02 % and a sialic content of 0.15 %. Chromatography of the 125I-labelled tumour TG revealed the presence of mono- and diiodothyrosines, a very small amount of triiodothyronine but no thyroxine. These results suggest that tumour TG, isolated in the experimental rat thyroid tumour, previously shown not to incorporate sialic acid into thyroglobulin, has a different electrophoretic mobility from native TG but is very similar to desialylated rat TG and has a very low sialic acid and iodine content as well as a striking decrease in thyroxine.

Thyroid proteins and hormone synthesis in human thyroid cancer.

ABSTRACT Thyroid iodoproteins and hormone synthesis have been studied in vivo and in organ culture in 44 cases of thyroid cancer. In a few cases, Tg1) (17–19 S) is virtually absent; a portion of the light fractions (3–8 S), which seems to represent some precursors of Tg, incorporated in culture the 14C-amino acids. In most of the cases, the solubility profiles, sedimentation patterns as well as electrophoretic migration of proteins were normal. The content of Tg and the concentration of stable iodine (127I) in Tg are less than that of "normal" tissues, and the deficiency in iodination appears to be more pronounced than the depression of the Tg synthesis. Most frequently the radioiodine uptake is very low and most of the iodine remains in the gland as iodide and MIT. In those tissues which organify radioiodine, it is incorporated into tyrosine molecules and is metabolized to the stage of iodothyronines (T4 + T3); there must then be little or no defect in coupling reactions. There is a linear relation between the concentration of stable iodine in Tg and the level of hormone synthesis, as we have found in "normal" gland and benign thyroid diseases. These results suggest that the overall disorder seen in thyroid cancer tissues appears to involve one of the initial steps of hormone synthesis. The very low mean iodination of Tg in these tissues suggests a great heterogeneity in the functional activity throughout the tumour. TSH has a very variable effect on thyroid cancer tissues maintained in organ culture: in 46 % of the cases the hormone has no effect. In some instances TSH may significantly increase the incorporation of radioiodine into soluble iodoproteins, Tg as well as the albumin fraction.

Incorporation of carbohydrates into abnormal thyroglobulin in an experimental rat thyroid tumor.

Previous findings indicated that in line 1–1C2 of experimental rat thyroid tumor there is decreased secretion of 19S thyroglobulin associated with a lack of incorporation of sialic acid into thyroglobulin and sialyltransferase activity in the tumor. In the present work we studied another tumor line, 1–8, in which particle bound iodopro-tein is also increased. This tumor, however, secretes an abnormal form of thyroglobulin. Soluble and digitonin-solubilized iodoproteins were examined in tumor labeled in vitro with N-acetylmannosamine, galactose, mannose, N-acetyl-glucosamine, leucine and iodine. About half of each label except galactose and N-acetyl-mannosamine was in the pellet after digitonin extraction and the remainder was evenly distrib-uted between soluble and solubilized fractions. After galactose labeling, the soluble fraction con-tained relatively more labeled protein; after N-acetylmannosamine, the pellet content was higher but most of the remainder was in the soluble fraction. The soluble and so...

Isolation and characterization of soluble and particulate thyroid iodoproteins in human congenital goiter.

Soluble and particulate iodoproteins solubilized by detergent from in vivo 125I labeled congenital goiter, have been isolated and characterized. The soluble iodoproteins

Characterization and properties of thyroid iodoproteins from severely iodine-deficient rats.

The iodoproteins from goitrous rat thyroid glands (300–800 mg), obtained by prolonged (20 months) and severe iodine deficiency, were isolated and characterized. The animals were given a low iodine diet (2 μg 1/100 g diet) containing 125I for 81 days (approach to equilibrium) and then they were pulse—labeled with 131I and 3H—leucine 2 hr prior to sacrifice. Thyroglobulinlike iodoproteins represented only 5% of the total protein in the crude soluble extract with 19 S comprising 90% and 27 S 10%. There was almost no iodine in 19 S while 27 S contained 0.12% iodine. Therefore a large proportion of the iodine stored in the soluble iodoproteins was due to the iodine in the 27 S protein. The turnover of iodine in 27 S, however, was much slower than in 19 S. In these severely iodine deficient animals the distribution of soluble thyroid iodoproteins was not significantly different from that observed in normal glands; the low iodine content, however, affects the stability of thyroglobulin. The iodinefree 19 S was m...

Membrane-bound thyroglobulin in an experimental thyroid tumor of rats

Soluble and particulate iodoproteins have been studied in an experimental rat thyroid tumor (Wollman Line 1-1C 2) labeled by intraperitoneal injection of 125I-. The uptake of the tumor was very low (approx. 1% of the dose per g), and most of the radioactivity (75–95%) was particulate. The particulate iodoproteins were solubilized (10–78%) by vigorous rehomogenization and digitonin treatment; the soluble and solubilized proteins were analyzed by density gradient ultracentrifugation, microimmunodiffusion and double immunoprecipitation. Labeled 19-S thyroglobulin comprised 30–60% of the soluble iodoproteins and 10–90% of the total solubilized iodoproteins. In the iodoproteins solubilized by rehomogenization there was 10–23% 19-S at 60 min or less after injection, and most of the 125I sedimented at <6 S. This “light fraction” had a density similar to that of endoplasmic or plasma membranes and yielded 25–75% 19-S thyroglobulin when treated with digitonin. Subcellular fractionation showed that 62% of the total tumor 125I was in the “nuclear” fraction, 35% in the “microsomal” fraction and only 3% in the “mitochondrial” fraction, which should contain lysosomes. In vitro experiments failed to show non-specific adsorption of thyroglobulin as a source of membrane-bound thyroglobulin. The results suggest that in the tumor studied there is decreased synthesis of thyroglobulin and a possible defect in its release from cell membranes.

Abnormal iodoproteins in human congenital goiter.

Soluble iodoproteins from three congenitally goitrousthyroids have been isolated by salt fractionation followed by DEAE-cellulose chromatography, gel filtration and density gradient centrifugation and characterized by analytical ultracentrifugation, polyacrylamide electrophoresis and by immunological procedures. It has been shown that the amount of 19 S thyroglobulin is strikingly decreased, the soluble proteins consisting of several slow-sedimenting iodocompounds: (3 S-6S) not identified as any of the known thyroglobulin subunit. The immunological data suggest that some of the heterogenous 3 S-6 S fractions is related to the thyroglobulin metabolism.

Ultrastructure and soluble iodoproteins in human thyroid cancer.

ABSTRACT Investigations have been carried out on the ultrastructure and the soluble iodoprotein pattern of human thyroid cancer in both follicular and papillary carcinomata. The predominant ultrastructural features are: distention of the endoplasmic reticulum, moderate increase of free ribosomes or polysomes, mitochondria, and dense granules, and loss of basal membrane infoldings. Hyperplasia of microvilli and nuclear abnormalities are more pronounced in follicular carcinoma, whereas in papillary carcinoma the most characteristic alterations are: disorganization of mitochondria, reduction of attached ribosomes, partial transformation of rough into smooth endoplasmic reticulum, and appearance of lamellar concentric structures in the cytoplasm. The ultrastructural disorganization of the thyroid cells coincides with a striking decrease of 19S-thyroglobulin which is replaced by a heterogeneous slow-sedimenting material that has the immunological properties of serum globulins.

Effects of structure and iodine content of the rat thyroid on the distribution of 127-I and 131-I between particulate and soluble thyroidal protein-bound iodine.

The distribution of 127I between particulate and soluble iodoproteins and the labeling of these 2 PBI fractions with 131I were studied in rat thyroids whose structure, function and iodine content were manipulated by hypophysectomy, feeding of a low iodine diet, administration of goitrogens such as propylthiouracil (PTU) or NaClO4, and feeding of diets rich or poor in iodine during recovery from NaClO4 treatment. The percentage of thyroidal PB127I in particulate form, which is around 10 in normal rats on an iodine-sufficient or iodine-deficient diet, was lowered to 2.6 in the iodine-rich, atrophic glands of hypophysectomized rats; in hyperplastic glands, whose iodine concentration was low, it ranged from 5.5 to 17.4, showing no correlation with the degree of hyperplasia or the iodine content. Both in hypophysectomized and in iodine-deficient intact rats, the percentage of thyroidal PB131I in the particulate fraction leveled off at 5-7 within 4 hr after 131I injection, in spite of marked differences in thyr...

SOME PROPERTIES OF THE SOLUBLE IODOPROTEINS FROM NORMAL AND CERTAIN ABNORMAL THYROID GLANDS.

Some of the physicochemical properties of thyroglobulin obtained from normal and diseased thyroid glands have been studied. Properties of the soluble component from gland homogenates have been compared with those obtained after purification of thyroglobulin by chromatographic fractionation on Sephadex G-200. Purified thyroglobulins from both normal and diseased glands precipitated sharply between 1.57 and 1.75M phosphate buffer (equimolar KH2PO4and K2HPO4). On the other hand, the salting-out curves of the soluble supernatants were incomplete in this concentration zone, and a significant fraction of the protein remained soluble even in 2.45 molar phosphate buffer. By starch gel electrophoresis this soluble protein was found to be predominantly albumin. Similar abnormal salting-out curves could be obtained by using artificial mixtures of purified thyroglobulin and albumin. The salting-out of labeled thyroglobulin was not altered by admixture of albumin. The electrophoretic mobility of the thyroglobulin was ...

THYROIDAL IODOPROTEINS IN PATIENTS WITH GOITROUS HYPOTHYROIDISM.

The thyroids from 3 individuals with congenital goiters have been studied. Abnormal soluble iodoproteins and particulate iodoproteins have been identified and their specific activities have been measured. The specific activity of the most soluble iodoproteins ranged from 16 to 350% greater than that of thyroglobulin. The specific activity of the particulate iodoproteins varied from twice as great to less than one half as great as thyroglobulin. Immunological studies showed that, in the protein fraction soluble between 35 and 50% saturated ammonium sulfate, only a small portion behaved as thyroglobulin. A new soluble iodoprotein which is precipitated with ammonium sulfate at or below 35% saturated ammonium sulfate was found.