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Biomedical subjects

L J DeGroot

Publications and source records attributed to L J DeGroot.

At least 127 records · Page 7Linked to original sources
PubMed1989

Thyroid hormone nuclear receptors and their role in the metabolic action of the hormone.

Thyroid hormone nuclear receptor molecules have been characterized as proteins of approximately 49,000 molecular weight existing in cells attached to chromatin and with 4000-8000 copies per nucleus. They bind T3 with Ka of 0.2 X 10(10) l/mol and show microheterogeneity on isoelectric focusing. Hormone responsiveness varies with receptor content in the nucleus and occupancy of receptor by T3. Recent investigations have shown that the receptors are part of the v-erbA related super family of nuclear hormone receptors. At least two types of T3 receptors (TR) exist, one coded by a gene on chromosome 3 (TR beta) and a second coded on chromosome 17 (hTR alpha). Receptors are low in the fetus and, in the adult, are dramatically reduced by starvation, illness and glucagon. Receptors function through binding of T3 or other hormone analogs to a domain in the carboxyl portion of the protein, and binding of the receptor-T3 complex through 'DNA-fingers' to specific response elements as enhancers and located in the 5'-flanking DNA of thyroid hormone responsive genes. Extensive studies on regulation of rat growth hormone have suggested binding of receptor or associated factors to several positions in the 5'-flanking DNA, and recent studies suggest that a crucial area may be a 15 bp segment between bases -179 and -164. Abnormal receptors are believed to be responsible for the syndrome of generalized resistance to thyroid hormone action, but it is yet unclear as to which form (or forms) of the receptor is abnormal in this syndrome.

Amino Acid Sequence↗
PubMed1989

Treatment of Graves' disease and the course of ophthalmopathy.

PURPOSE: Contradictory results have been obtained with regards to the effect of various treatment modes on the exacerbation of Graves' ophthalmopathy, probably because the number of patients in each study was small and some studies were analyzed only in relation to one type of treatment. To circument these problems, we studied the course of Graves' ophthalmopathy after various modes of therapy for thyrotoxicosis among 537 patients with Graves' disease. PATIENTS AND METHODS: A total of 537 patients with Graves' disease were prospectively studied over an 11-year period. Thirty-one patients were lost to follow-up during the first six months after treatment and were excluded from the study. Of those remaining, 426 received one form of treatment, 79 received two kinds of therapy, and one received three kinds of therapy. Thus, surgical treatments numbered 164, radioactive iodine-131 (131I) treatments numbered 241, and medical treatments numbered 182. Ocular signs were considered improved or exacerbated by the following criteria: decrement or increment of the exophthalmos of 2 mm or more, improvement or deterioration of visual acuity, and regression or progression of extraocular muscle involvement causing diplopia. RESULTS: Among patients who did not have infiltrative ophthalmopathy before treatment, there was no difference in the occurrence of posttreatment exophthalmos in the surgically, medically, and 131I-treated patients (7.1%, 6.7%, and 4.9%, respectively). The incidence and the degree of progression of ophthalmopathy in patients who already had exophthalmos before treatment were similar in the medically, surgically, and 131I-treated groups (19.2%, 19.8%, and 22.7%, respectively). Most of the progression occurred in the posttreatment euthyroid stage. The incidence of improvement of ophthalmopathy was also similar (14.1%, 12.6%, and 12.3% in the medically, surgically, and 131I-treated patients). CONCLUSION: In conclusion, we found no influence of type of therapy for thyrotoxicosis on the clinical course of Graves' ophthalmopathy in this retrospective study of 537 patients.

Adult↗
PubMed1989

Generalized resistance to thyroid hormone associated with a mutation in the ligand-binding domain of the human thyroid hormone receptor beta.

The syndrome of generalized resistance to thyroid hormone is characterized by elevated circulating levels of thyroid hormone in the presence of an overall eumetabolic state and failure to respond normally to triiodothyronine. We have evaluated a family with inherited generalized resistance to thyroid hormone for abnormalities in the thyroid hormone nuclear receptors. A single guanine----cytosine replacement in the codon for amino acid 340 resulted in a glycine----arginine substitution in the hormone-binding domain of one of two alleles of the patient's thyroid hormone nuclear receptor beta gene. In vitro translation products of this mutant human thyroid hormone nuclear receptor beta gene did not bind triiodothyronine. Thus, generalized resistance to thyroid hormone can result from expression of an abnormal thyroid hormone nuclear receptor molecule.

Alleles↗
PubMed1989

Expression of three forms of thyroid hormone receptor in human tissues.

At least two thyroid hormone receptor (hTR) genes are present in humans, but the significance of this multiplicity is unknown. These receptors could have differences in tissue distribution or possess different functions. We studied the distribution and abundance of three hTR mRNAs (hTR beta, hTR alpha 1, and hTR alpha 2) by Northern blot analysis. Three mRNAs were expressed in all tissues examined. hTR beta was strongly expressed in brain and prostate predominantly as a 10.0-kilobase (kb) mRNA. This mRNA was also expressed in thyroid and was much less abundant in liver, kidney, placenta, tonsil, and spleen. hTR alpha 1 is represented by two mRNAs with sizes of 6.0 and 3.2 kb. The 6.0-kb mRNA was constantly less abundant than the 3.2-kb mRNA. hTR alpha 2 was detected as a single mRNA with a size of 3.2 kb, using a probe unique for this mRNA. Both hTR alpha 1 and hTR alpha 2 were strongly expressed in brain, prostate, and thyroid and much less in other tissues. The relative amounts of the three hTR mRNAs were roughly parallel in each tissue. It is of interest that none of these hTRs was abundant in liver, which is the major thyroid hormone-responsive organ. Another hTR may be present in liver.

Blotting, Northern↗
PubMed1989

Stabilization, accurate determination, and purification of rat liver nuclear thyroid hormone receptor.

Rat liver nuclear thyroid hormone receptor lost 3.5.3'-tri-iodo-L-thyronine (T3)-binding activity with a half-life of 14 days, 4h, 139 min, 62 min, 16 min or 6 min at 0, 36, 38, 40, 43 or 45 degrees C respectively, when present in crude nuclear extracts. Glycerol increased the half-life of the receptor during heat inactivation. Protection was reversible by removing the glycerol. The receptor was unstable at a pH below 6.0 or above 10.0. We also found a loss of the receptor activity during the separation of bound and free hormone using the resin test. Of several conditions tested for the separation of bound and free hormone, the addition of heated nuclear extract gave the most accurate estimation of bound hormone when using the resin test. Using these characteristics of the receptor, we purified the receptor to 1220 pmol T3-binding capacity/mg protein with a final yield of 14.6 micrograms/4 kg rat liver.

Animals↗
PubMed1988

Comparison of complement fixation and radioassay techniques to detect solubilized human thyroid microsomal antigenic activity.

Although recently the human thyroid microsomal antigen (M-Ag) has been possibly identified as the thyroid peroxidase, its nature remained unknown over almost three decades. One of the difficulties encountered in the identification of M-Ag derived from the conflicting data obtained in the attempts to solubilize active antigenic material from thyroid subcellular fractions. In particular, following detergent treatment, M-Ag could not be detected by complement fixation, while a full recovery of the antigen has been observed using a radioassay technique. In the present investigation, the antigenic activity of Triton X-100 solubilized thyroid microsomes was assessed in parallel by complement fixation and radioassay methods employing the same anti-microsomal antibody (anti-M Ab) preparation for antigen detection. In untreated microsomes antigenic activity was detected by both methods. In contrast, detergent solubilized M-Ag was detected by radioassay, but could not be detected by complement fixation. These data indicate that detergent solubilization diminishes the complement fixing capacity of M-Ag, while the solubilized antigen can still be fully detected by its binding reaction with the autoantibody, and explain the discrepant results obtained in previous studies.

Autoantibodies↗
PubMed1988

Binding of thyroid hormone receptor-associated factors to rGH gene 5' flanking sequences.

Binding of semi-purified rat liver triiodothyronine (T3) nuclear receptor (T3-nR) to sequences in the 5' flanking DNA of rat growth hormone (rGH) has been evaluated by the DNAse-footprinting technique. T3-nR was obtained by extraction in 0.3 M KCl and partially purified by column chromatography to 80 pmol/mg T3 maximal binding capacity (MBC). The T3-nR preparation protects the sequence -330 to -314 (5'-CAGTGAACAAACGATG-3') which may represent a repressor element, the sequence -224 to -192 (5'-CATTGCCCATAAACCTGAGC-3') which is thought to involve positive T3 regulation, the sequence -98 to -78 (5'-GCTCCAGCCATGAATAAATG-3') which may regulate basal expression, and the TATA box area. Although the DNAse footprints occur only with preparations containing functional T3-nR, it is uncertain whether each protected zone is due to binding of T3-nR or associated proteins. Protection is associated with enhanced DNAse digestion around the protected sites, involves both strands, and does not appear to require T3 occupancy of the receptor. Only the areas described are protected in the studies, and non-specific proteins such as albumin, core histones, and nuclear extracts without receptor activity, have no effect. A putative consensus enhancer sequence -CCAGAGCCAAGG- conveying T3 responsivity is suggested on the basis of comparison to sequences in four T3 responsive genes.

Animals↗
PubMed1988

Radiation and thyroid disease.

External irradiation of the thyroid causes the subsequent development of thyroid malignancies at an approximate rate of 5 per rad per million people per year. There is no certain lower threshold, but possibly doses above 3000 rads are less effective. The tumours produced are primarily differentiated malignancies typical of non-irradiated patients, and the clinical course is similar. Most radiation-associated malignancies followed treatment given for enlarged thymic glands, enlargement of the tonsils or adenoids, and acne. Currently patients are seen with radiation-associated thyroid disease following treatment of malignant tumours in the neck. Diagnostic manoeuvres are similar to those used in non-irradiated individuals, but multinodularity is probably an indication for operation. Because of the high incidence of multicentricity, we prefer near-total thyroidectomy if cancer is found. Prophylactic thyroid hormone administration is of uncertain value in preventing the development of tumours. X-ray to the thyroid also can induce other histologic abnormalities, including a high incidence of adenomas and hypothyroidism, and is associated with an increased incidence of autoimmune thyroid disease and possibly the development of exophthalmos and Graves' disease. In contrast to the obvious effects of external irradiation, 131I diagnostic tests and treatments have not been associated with a clearly increased incidence of thyroid malignancy.

Humans↗
PubMed1988

Characterization of a thyroid hormone receptor expressed in human kidney and other tissues.

A cDNA encoding a specific form of thyroid hormone receptor expressed in human liver, kidney, placenta, and brain was isolated from a human kidney library. Identical clones were found in human placenta and HepG2 cDNA libraries. The cDNA encodes a 490-amino acid protein (Mr, 54,824). When expressed and translated in vitro, the protein product binds triiodothyronine with Ka of 2.3 X 10(9) M-1. This protein, designated human thyroid hormone receptor type alpha 2 (hTR alpha 2), has the same domain structure as other members of the v-erbA-related superfamily of receptor genes. It is similar to thyroid hormone receptor type alpha described in chicken and rat and less similar to human thyroid hormone receptor type beta (formerly referred to as c-erbA beta) from placenta. However, it is distinguished from these receptors by an extension of the C-terminal hormone binding domain making it 80 amino acids longer than rat thyroid hormone receptor type alpha 1 [Thompson, C.C., Weinberger, C., Lebo, R. & Evans, R. M. (1987) Science 237, 1610-1614]. Different sizes of mRNA found in liver (2.5 kilobases) and kidney (2 kilobases) suggest there may be tissue-specific processing of the primary transcript of this gene. Identification of human thyroid hormone receptor type alpha 2 indicates that two or more forms of thyroid hormone receptor exist in human tissues and may explain the normal variation in thyroid hormone responsiveness of various organs and the selective tissue abnormalities found in the thyroid hormone resistance syndromes.

Amino Acid Sequence↗
PubMed1988

Characterization of the thyroid microsomal antigen, and its relationship to thyroid peroxidase, using monoclonal antibodies.

MAb directed to the thyroid microsomal antigen have been developed. All bound to 101- and 107-kD bands in Western blot analysis using thyroid microsomal fraction as antigen. The MAb also bound to microsomal proteins immunoprecipitated by serum from patients having a high titer of anti-microsomal antibody but no antibodies to thyroglobulin or thyrotropin-stimulating hormone receptor. The pattern of binding was related to the amount of reducing agent. The 101- and 107-kD bands were increased by addition of dithiothreitol whereas, in its absence, numerous bands of higher molecular weight were present, suggesting a multimeric protein structure. Despite the inability to immunoprecipitate thyroid peroxidase (TPO) enzymatic activity, the MAb bound intensively in Western blot to denatured purified hog TPO and to denatured immunopurified human TPO. Trypsin digestion of the 101-107-kD antigen produced a doublet of 84-88 kD that was still immunoreactive with MAb. One of five polyclonal sera tested (with a microsomal antibody titer greater than 1/20,480 measured by the tanned red cell hemagglutination technique) also recognized the 84-88 kD trypsin fragments. Addition of V8 protease led to a disappearance of the 107-kD protein, but not the 101-kD protein, proving that this antigen is formed by two different polypeptides. The MAb bound strongly to thyroid epithelium, whereas binding to papillary carcinoma was absent or low and moderate for follicular and Hurthle cell carcinoma. This study indicates that the thyroid microsomal antigen and TPO are identical and are constituted of two different polypeptides. On SDS-PAGE the antigen appears as two contiguous bands which share common epitopes but are not identical, as proven by their size and difference in susceptibility to proteolytic digestion. The immunoreactivity of the molecule is highly dependent on a trypsin-sensitive site, which appears important in the recognition of the antigen by polyclonal sera and may have biological importance. The expression of microsomal antigenicity is variable among various thyroid carcinomas.

Antibodies, Monoclonal↗
PubMed1988

Microsomal antigen-reactive lymphocyte lines and clones derived from thyroid tissue of patients with Graves' disease.

Thyroid mononuclear cells (TMC) were maintained in long term cocultures with thyroid fibroblasts and thyroid epithelial cells from patients with Graves' disease, using medium supplemented with thyroid microsomal antigen (McAg) and IL-2. The TMC consisted predominantly of T4+ (CD4+, helper) and, to a lesser extent, T8+ (CD8+, cytotoxic/suppressor) lymphocytes, with a small number of macrophages and natural killer cells. The average T4+ to T8+ ratio was 3.2. From these cultures we obtained thyroid T cell lines and clones reactive to thyroid antigens. T Cell lines were tested in a microproliferation assay using thyroglobulin (Tg), McAg, tetanus toxoid, and IL-2. Of 14 lines from 6 patients, 2 proliferated in response to McAg when TMC plus thyroid fibroblasts were used as antigen-presenting cells. Clones of thyroid lymphocytes were obtained by culturing cells at limiting dilution with IL-2, McAg, and different types of autologous accessory cells. Peripheral blood mononuclear cells plus skin fibroblasts provided the best source of accessory cells, allowing near 100% cloning efficiency. Of 26 clones tested, 6 recognized McAg, 2 were Tg reactive, and 3 were autoreactive. All phenotyped clones were of the T4+ phenotype. Our method results in production of thyroid T cell lines and clones. The fibroblasts probably provided growth factors and/or collaborated with peripheral blood mononuclear cells as antigen-presenting cells. These lines and clones from patients with Graves' disease were predominantly helper T cells, in contrast to the previously demonstrated cytotoxic/suppressor cell predominance in cells from patients with Hashimoto's thyroiditis. This difference in cell function may help explain the differing clinical courses of these two closely related autoimmune thyroid diseases. The availability of long term microsomal antigen-specific T cell clones should allow careful analysis of the role these cells play in thyroid autoimmunity.

Antigens↗
PubMed1988

Characterization of a third human thyroid hormone receptor coexpressed with other thyroid hormone receptors in several tissues.

A cDNA that encodes a third type of human thyroid hormone receptor (hTR alpha 1) has been isolated from a skeletal muscle library. The cDNA encodes a 410 amino acid protein, Mr = 46,820. When expressed and translated in vitro, hTR alpha 1 binds T3 with an association constant (ka) of 1.8 x 10(9) M-1. Comparison of the DNA sequence of hTR alpha 1 and a previously identified alpha type thyroid hormone receptor (hTR alpha 2) suggests that they could be transcribed from the same gene, and that alternative RNA splicing results in the synthesis of either hTR alpha 1 or hTR alpha 2. Two mRNA (3.2 kilobases and 6 kilobases) of hTR alpha 1 have been detected in several tissues. At least three types of thyroid hormone receptors (hTR alpha 1, alpha 2, beta), which possess similar affinities for hormone ligands, can be expressed in the same tissue.

Amino Acid Sequence↗
PubMed1988

Auto-anti-idiotype antibody against anti-thyroglobulin auto-antibody in humans.

Anti-idiotype antibodies (Anti-Id Ab) are believed to normally exert a form of feedback control on Ab production. An abnormality in this network might lead to excess Ab production. To detect the abnormalities in immunoregulation in autoimmune thyroid disease, we tried to demonstrate anti-Id Ab to anti-thyroglobulin antibody (ATA) and to correlate them to the clinical course of disease. We developed two assays, one based on the binding of anti-Id Ab to ATA (Id) and a second on the inhibitory activity of anti-Id Ab in the reaction of human thyroglobulin (hTG) and ATA. We could not demonstrate anti-Id Ab in either assay. Possibly anti-Id Ab to ATA is not formed sufficiently to be detected in our assays, or is only present in specific phases of the course of autoimmune thyroid disease. During studies of anti-Id Ab we found "pepsin site" Ab in patients and normal subjects. We developed a new solid phase radioimmune assay for this Ab, an antibody which reacts with antigens exposed on IgG when F(ab')2 fragments of IgG are prepared. The incidence of this Ab did not differ between patients and normal subjects. IgG from patients with autoimmune thyroid disease which contained high levels of anti-pepsin site Ab, did not show any specificity for ATA (Id), nor did it inhibit the reaction between hTG (Ag) and ATA (Id). The importance of this anti-F(ab')2 antibody remains to be determined, but it does not represent an anti-Id Ab.

Antibodies, Anti-Idiotypic↗
PubMed1987

Antibody against nuclear thyroid hormone receptors.

Rat liver nuclear thyroid hormone receptor was purified to 700-1600 pmol T3 binding capacity/mg protein by sequentially using hydroxylapatite column, ammonium sulfate precipitation, Sephadex G-150 gel filtration, DNA-cellulose column, DEAE-Sephadex A-50 column, and heparin-Sepharose column. Serum from a mouse immunized using this purified receptor preparation caused a shift of [125I]T3-receptor peak on glycerol density gradient sedimentation from 3.4 S to approximately 7 S. [125I]T3-receptor complex was immunoprecipitated using this serum and goat anti-mouse IgG. The serum showed reduced ability to immunoprecipitate the globular T3 binding fragment with Stokes radius of 22 A produced by trypsin digestion, a receptor fragment which has core histone and hormone binding but not DNA binding activity. These data indicate the production of anti-nuclear thyroid hormone receptor antibody which mainly recognized epitopes unrelated to hormone and core histone binding domain.

Animals↗
PubMed1987

Characterization of nuclear thyroid hormone receptors of cultured skin fibroblasts from patients with resistance to thyroid hormone.

Nuclear thyroid hormone receptors of patients with the syndrome of resistance to thyroid hormone were investigated in cell lines from seven patients in four affected families and compared to results from six normals. Fibroblasts cultured from skin biopsies were used. When binding affinity and capacity for L-triiodothyronine (T3) were examined by incubating whole cells or isolated nuclei, no significant differences were found. The amount of receptor released during the incubation of nuclei (9.3% to 19.0% of total nuclear receptors) was also within the normal range in these patients. When T3 binding assays were performed on 0.3 mol/L KCl extracted receptor, a significant decrease in binding capacity (MBC) without a difference in binding affinity (Ka) was observed in four patients and a lower Ka with normal MBC was found in two patients. Recovery of receptors in saline extracts, from patients' fibroblasts showing a low MBC, was low in comparison to normals. Lability of salt extracted receptors at 38 degrees C was normal and salt extractability of T3 occupied receptors, examined by incubation of [125I]-T3 labeled nuclei with various concentrations of KCl, was only slightly decreased. This lower salt extractability of receptors was insufficient to account for the low MBC obtained by Scatchard analysis of T3 binding to nuclear extracts. Gel filtration and density gradient sedimentation of salt-extracted receptors showed Stokes radius of 34 A, and sedimentation coefficient of 3.4 S in all patients and normals. From these values, molecular weight of 49,000 and total frictional ratio (f/fo) of 1.4 were calculated for nuclear receptors from patients and normals, suggesting a somewhat asymmetrical shape of receptors.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗