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M Derwahl

Publications and source records attributed to M Derwahl.

At least 37 records · Page 2Linked to original sources
PubMed1996

Expression of apoptosis-related proteins in thyroid tumors and thyroid carcinoma cell lines.

Whereas in normal human thyroid tissue total cell mass is maintained by a balance between cell proliferation and apoptosis, the programmed cell death, in thyroid tumors this equilibrium is disrupted. In tumor cells, an augmented proliferation rate is no longer counterbalanced by an equally enhanced apoptosis resulting in an increased netto growth rate. To investigate regulation of apoptosis in thyroid tumors, we analyzed the expression of apoptosis-related proteins of the bcl-2 family in human thyroid tissues and in the human thyroid carcinoma cell lines FTC 133, HTC, HTC-TSHr and HTh74. In comparison to normal tissue, we detected an increased expression of the anti-apoptotic protein bcl-2 in adenomas, whereas follicular carcinomas showed various expression of bcl-2 with decreased levels in 32% of cases. BclxL expression was comparable in all tissues examined. The pro-apoptotic protein bax was expressed at lower levels in carcinomas than in adenomas, whereas bak and bclx were expressed in the same order of magnitude in all tissues examined. In contrast, thyroid carcinoma cell lines exhibited a relatively strong expression of bclxL, but a weak expression of bcl-2. In all four cell lines, the amounts of the pro-apoptotic proteins bax, bak and bclx were higher than in most tumor tissues. Our data show that in thyroid tumors expression of members of the bcl-2 protein family is not uniform. Rather, the expression pattern of pro- and anti-apoptotic proteins in thyroid tumors is heterogeneous. This may, at least in part, reflect the futile attempt of tumor cells to counterbalance the action of growth-promoting factors in thyroid tumor-igenesis.

Adenoma↗
PubMed1996

Molecular aspects of the pathogenesis of nodular goiters, thyroid nodules and adenomas.

One of the most significant results of recent molecular thyroid research on the pathogenesis of nodular goiters may be the finding that not only thyroid adenomas but also many thyroid nodules are clonal in origin and thus are true benign tumors. Both clonal and polyclonal nodules may coexist within the same nodular goiter. Since clonal nodules may secondarily acquire a heterogeneous phenotype, they can become morphologically indistinguishable from polyclonal lesions. The molecular mechanisms that generate thyroid nodules and adenomas are still poorly understood. Certainly, the recent detection of activating mutations in the TSH receptor and the Gs alpha gene in a subset of toxic thyroid adenomas and nodules may explain the generation of hyperfunction in these tumors, but there is strong evidence that these mutations are not the unique and primary cause of tumor formation. In this respect the concept of natural occurring heterogeneity of thyroid growth and function can provide a plausible explanation for the early stages of nodular transformation: If a thyrocyte has a high intrinsic growth potential or if it is affected by overexpression of a protooncogene or a growth factor or hit by an oncogene or other molecular events, the cell will outgrow and form a tumor. The inborn qualities of proliferating cells or the sequence of various genetic alterations in proliferating cells will in turn determine the phenotype and function of the tumor.

Adenoma↗
PubMed1996

Mutations of the TSH receptor as cause of congenital hyperthyroidism.

4 patients of two families with congenital persistent hyperthyroidism without detectable autoantibodies are reported. The members of the first family affected by hyperthyroidism, i.e. the mother and her two children, showed a germline mutation, a transition of GCC to GTC in the genomic DNA of the TSH receptor, leading to an exchange of alanine by valine at the position 623. The mother was thyroidectomized at two times because of recurrent nodular goiter. The third child of a healthy second family showed a transition of AGC to AAC leading to an exchange of serine by asparagine at the position 505 of the TSH receptor. The mutation of family 1, as a somatic point mutation leading to autonomous thyroid adenoma, has originally been demonstrated to constitutively activate TSH independent cAMP accumulation. The functional tests of the TSH receptor gen mutation, detected in family 2, are ongoing, but an exchange of serine by arginine at the same position has been shown to lead to constitutively active cAMP accumulation. The cases of congenital hyperthyroidism in the first family lead to a reduction of the birth weight and head circumference and to a neonatal but not fetal tachycardia. Bone age of both children was accelerated by one year. In contrast to that, congenital hyperthyroidism of the second family lead to more marked signs of intrauterine hyperthyroidism. The mother observed marked symptoms of fetal and neonatal hyperthyroidism. The bone age at a chronological age of 6 months was 4-6 years and the neonate showed a mild exophthalmus. We conclude, that congenital hyperthyroidism due to constitutively activating TSH receptor mutations has to be considered, if hyperthyroidism is not transient but persistent, and the parameters of autoimmunity are absent. Constitutively active TSH receptor germline mutations lead to different degrees of congenital hyperthyroidism. In contrast to patients with Graves' disease, more aggressive means of treatment like total thyroidectomy and/or radiation seem to be recommendable in cases with severe hyperthyroidism to control the disease.

Base Sequence↗
PubMed1996

Constitutive activation of the Gs alpha protein-adenylate cyclase pathway may not be sufficient to generate toxic thyroid adenomas.

In toxic thyroid adenomas, mutations in the TSH receptor (TSH-R) gene or the gene encoding the alpha-subunit of the stimulatory guanine nucleotide-binding protein (Gs alpha) have been demonstrated to constitutively activate the cAMP cascade, which subsequently stimulates the growth and function of these tumors. However, the widely varying thyroid phenotypes in patients with TSH-R germline mutations, ranging from only slightly enlarged diffuse to multinodular goiters, suggest that additional mechanisms may be effective in the pathogenesis of toxic adenomas. We have investigated the levels of stimulatory and inhibitory G protein alpha-subunits together with basal and TSH-stimulated adenylate cyclase (AC) activity in toxic adenomas with or without activating mutations and in nodular and extranodular tissues of a toxic goiter due to a germline mutation in the TSH-R gene. Augmented expression of Gs alpha protein was detected in all toxic adenomas, independent of the presence of mutations, and in the nodular tissue of the toxic goiter, but not in the nonnodular hyperplastic tissue of the toxic goiter with the mutated TSH-R. Analogously, the expression of the alpha-subunit of the inhibitory G protein (Gi alpha) was also increased in all adenomas and the nodular tissue of the goiter, but, again, not in the hyperplastic goiter tissue. Basal AC activity was high in all tissues with mutations, but was only slightly increased in adenomas without detected mutations. No correlation was detectable between basal or TSH-stimulated AC activity and the levels of Gs alpha and Gi alpha. Our data suggest that mutational activation of the cAMP cascade may not be sufficient to generate toxic nodules and adenomas, but far more complex mechanisms, including alterations of G protein signaling, may be effective in the pathogenesis of these tumors.

Adenoma↗
PubMed1996

TSH receptor and Gs-alpha gene mutations in the pathogenesis of toxic thyroid adenomas--a note of caution.

The detection of a constitutive activation of the AC cascade by TSH-R and Gs alpha mutations in a number of TTAs should not distract from the large gap in our understanding of the pathogenesis of thyroid tumors. TTAs form only a minor fraction of all thyroid nodules, and even within this small subgroup, activating mutations have been found regionally with a highly variable incidence. If activating mutations were the sole and only cause of TTAs, a homogeneous functional and morphological response of all thyrocytes would ensue. This, however, is not the case. Rather, severe disturbances of the Gs protein-AC cascade regularly occur in TTAs. Even within thyroids affected by activating TSH-R germline mutations, some cell clones proliferate at a faster rate than others, causing nodular growth with time. Moreover, not only functional, but also morphological heterogeneity very frequently evolves even in clonal adenomas. The natural heterogeneity among individual thyrocytes may account for a different functional and proliferative response among cells affected by identical mutations or any other gain-of-function event. The recent findings in toxic adenomas must be taken together with the fact that, in the large majority of all thyroid nodules, iodine metabolism is by no means enhanced, but diminished or absent and that, in this type of tumor, no consistent pattern of growth-stimulating mutational events has yet been identified. The nature, the precise temporal sequence and interaction of the genetic, cytogenetic, and environmental events that cause the very common and often autonomous nodular growth of only a few distinct cell populations within the human thyroid gland remain largely unknown.

Adenoma↗
PubMed1995

Mechanisms of nonneoplastic endocrine hyperplasia--a changing concept: a review focused on the thyroid gland.

An important part of clinical endocrinology deals with diseases caused by benign and malignant nodules growing within originally homogeneous endocrine glands. In the search for the pathogenesis of these nodules, two concepts have been advanced: either the hyperplastic tissue is considered to result from chronic intense stimulation by a trophic hormone, eventually causing the growth of polyclonal nodules (a concept known as NNEH) or else, the nodules are thought to represent true clonal tumors. It has been realized rather recently that NNEH accounts only for a small minority of rare endocrine diseases, with the exception of highly prevalent iodine deficiency goiters and, in a broader sense, for Graves' disease. Indeed, secondary hyperplasia of endocrine glands resulting from long-lasting chronic hormonal overstimulation cannot explain a large number of essential features of the diseased glands. As best documented for the thyroid gland, outstanding among the characteristics of hyperplastic glands that do not fit into the simple concept of NNEH are the inevitable nodular transformation, the frequent autonomy and irreversibility of nodular growth, the loss of function in many cells and nodules, and the tremendous regional heterogeneity of growth and function including loss of coordination between these two main features of any living cell. Hyperplasia resulting from long-lasting stimulation by a trophic hormone is not a fully reversible process, as is often thought, but definitely increases the total cell mass and leaves behind, after cessation of the stimulus, a population of newly generated cells. This process is common to NNEH and true neoplastic growth. A review of common and disparate traits between endocrine hyperplasia and neoplasia must be based on the following generally accepted facts (excluding in-depth consideration of malignancy). 1. Many endocrine tumors are clonal while others are polyclonal. For example, pituitary and sporadic parathyroid adenomas are nearly always clonal while in the thyroid, multiple clonal nodules of different origin may coexist with polyclonal nodules. 2. Clonal growth does not necessarily indicate that the autonomous expansion of a tumor is driven by presently known genetic gain-of-function or loss-of-inhibition mutations or by cytogenetic aberrations. 3. Genetic mutations and chromosomal aberration in endocrine tumors are not necessarily primary events in the tumorigenesis but may as well be a late secondary phenomenon in growing tissue. 4. Clonal nodules may overgrow from primarily polyclonal ones. The best evidence to date comes from the rare clonal parathyroid adenomas with allelic loss of chromosome 11 evolving in tertiary hyperparathyroidism.(ABSTRACT TRUNCATED AT 400 WORDS)

Goiter, Nodular↗
PubMed1995

Expression of functional stimulatory guanine nucleotide binding protein in nonfunctioning thyroid adenomas is not correlated to adenylate cyclase activity and growth of these tumors.

In thyroid cells, the alpha-subunit of the stimulatory guanine nucleotide binding protein (Gs alpha) acts as signal transducer between the TSH receptor and the adenylate cyclase (AC), and it regulates both growth and function. In order to analyze Gs alpha expression by both Western blot analysis and in situ, we generated an antibody raised against a recombinant human Gs alpha protein. With this antibody, a strong cytoplasmic Gs alpha-immunostaining was detectable in cultured human thyroid cells and in TSH-stimulated rat thyroids, in contrast to normal human thyroids and to T4-treated rat thyroids, which showed only weak immunoreactivity. We obtained the following results by immunohistochemistry and Western blot analysis of 32 actively growing human thyroid adenomas: 1) strong Gs alpha expression in 11 adenomas, including 4 hyperfunctioning nodules, 1 of these with a point mutation in codon 201 of the Gs alpha gene; 2) no expression or only weak Gs alpha expression in 13 adenomas; and 3) a pattern of Gs alpha-positive and Gs alpha-negative cells in the remaining 8 adenomas. In addition, we analyzed ADP-ribosylation of Gs alpha and AC activity in 9 nonfunctioning adenomas and found a significant correlation between Gs alpha immunoreactivity and ADP-ribosylation and no correlation of both with basal and TSH-stimulated AC activity. In both types of adenomas, i.e. those with high as well as low Gs alpha, an indistinguishably high fraction of proliferating cells was detectable. We conclude that expression of functional Gs alpha protein in nonfunctioning thyroid adenomas is neither correlated to the basal or TSH-stimulated AC activity nor to the proliferation rate of these tumors.

Adenoma↗
PubMed1994

[Molecular aspects in the pathogenesis of nodules and adenomas of the thyroid gland].

Recent advances in thyroid research are reviewed which reflect fundamental changes in understanding of the pathogenesis of thyroid adenomas, and of clonal and polyclonal goiter nodules. It is generally accepted that chronic iodine deficiency leads to the development of a diffuse homogeneous goiter. However, low iodine supply does not explain generation and growth of thyroid nodules and the characteristic functional heterogeneity of most nodular goiters. Molecular analyses of recent years have revealed that thyroid adenomas and most nodules in goiters, even if morphologically heterogeneous, are clonal and thus true benign tumors. This has been demonstrated in areas both with iodine deficiency and with sufficient iodine supply. However, in areas with iodine deficiency, chronic stimulation accelerates the genesis of nodules and adenomas. The molecular pathogenesis of these tumors is still unknown. Only in a subgroup of toxic adenomas mutations of the TSH receptor and the Gs-alpha gene have recently been found that may explain the genesis of these tumors and the development of hyperthyroidism in patients with these adenomas.

Adenoma↗
PubMed1994

Interaction of human chorionic gonadotropin (hCG) and asialo-hCG with recombinant human thyrotropin receptor.

hCG is a putative thyroid stimulator. The present studies were undertaken to examine its interaction and that of its desialylated variant asialo-hCG with recombinant human TSH (hTSH) receptor (hTSHr). To this end, we transfected a human thyroid carcinoma cell line (HTC) lacking endogenous TSHr with the full-length cDNA of the hTSHr. Unlike the wild type, the transfected cells, termed HTC-TSHr cells, were able to bind bovine TSH (bTSH) with high affinity and increase cAMP production in response to bTSH stimulation. Of the hCG forms, intact hCG displayed a weak activity to inhibit [125I] bTSH binding to HTC-TSHr cells, with 100 mg/L (2.6 x 10(-6) mol/L) producing maximally a 20% inhibition, whereas asialo-hCG achieved half-maximum binding inhibition at a concentration of 8 mg/L (2.3 x 10(-7) mol/L). The inhibitory constant (Ki) of asialo-hCG for recombinant hTSHr was calculated from saturation experiments in the presence of variable doses of bTSH and a fixed concentration of asialo-hCG to be approximately 8 x 10(-8) mol/L. The interaction of asialo-hCG with TSHr was further assessed by studies of the direct binding of the radioactively labeled hormone to both HTC and HTC-TSHr cells. [125I]Asialo-hCG binding to HTC-TSHr cells was 4.7%, compared to 1.5% in the wild-type cells lacking TSHr and was displaceable by bTSH (0.1-100 IU/L), indicating specific binding of the tracer to TSHr. Functionally, hCG (up to 100 mg/L; 2.6 x 10(-6) mol/L) proved unable to evoke any significant cAMP response over basal values in HTC-TSHr cells, as did asialo-hCG. Asialo-hCG, but not hCG, inhibited bTSH-stimulated adenylate cyclase activity in the cells in a dose-dependent manner. In conclusion, the present data show that intact hCG binds only weakly to HTC-TSHr cells and produces no significant cAMP stimulation, which is at variance with data obtained in FRTL-5 and Chinese hamster ovary-TSHr cells, but in good accord with previous findings in human thyroid membranes. Asialo-hCG, on the other hand, strongly binds to recombinant TSHr and inhibits the cAMP response to bTSH in HTC-TSHr cells, indicating that the desialylated hCG variant directly interacts with the receptor and truly is an antagonist of the hTSHr.

Asialoglycoproteins↗
PubMed1993

Expression of the human TSH receptor in a human thyroid carcinoma cell line that lacks an endogenous TSH receptor: growth inhibition by cAMP.

The role of TSH and its receptor in controlling growth of thyroid carcinomas is far from well understood. In order to study this subject further we established a new human thyroid carcinoma cell line. We transfected human thyroid carcinoma cells lacking an endogenous TSH receptor with the human TSH receptor cDNA. Transfected cells, designated HTC-TSHr, expressed the TSH receptor mRNA and synthesized a functional TSH receptor with a TSH binding affinity in the order of magnitude of normal thyroid cells. In response to TSH stimulation HTC-TSHr cells accumulated cAMP, indicating a functional TSH receptor-adenylate cyclase system. However, HTC-TSHr cells did not concentrate iodide and lacked thyroglobulin immunoreactivity, although they did express low amounts of thyroglobulin mRNA. Proliferation of HTC-TSHr cells was inhibited by dibutyryl-cAMP and forskolin and also by TSH via the re-expressed TSH receptor.

Base Sequence↗
PubMed1992

Malignant transformation of rat thyroid cells transfected with the human TSH receptor cDNA.

Growth and function of well differentiated FRTL-5 thyroid cells depend on thyrotropin as its main regulatory hormone. We demonstrate here that stable transfection of FRTL-5 cells with the human thyrotropin receptor cDNA results in cellular transformation of these cells with altered cell shape and loss of contact inhibition. The transformed cells replicate in soft agar and form invasive tumors when cell suspensions are implanted onto nude mice. They have lost their thyrotropin dependent growth and their ability to concentrate iodide and synthesize thyroglobulin. But they still express the rat thyrotropin receptor mRNA and accumulate cAMP in response to thyrotropin stimulation. However, although the full length human thyrotropin receptor cDNA is integrated into their genome, transformed cells do not express the human thyrotropin receptor mRNA.

Animals↗
PubMed1990

Generation of intercellular heterogeneity of growth and function in cloned rat thyroid cells (FRTL-5).

The most characteristic hallmarks of human nodular goiters are nodular growth and heterogeneity of structure and function between different areas of the same goiter. In search of the earliest detectable stage of thyroid heterogeneity we have observed doubling times, TSH dependency, and thyroglobulin production in colonies formed from individual FRTL-5 cells growing as monolayers in slide flasks. Single cells and the colonies derived thereof were followed on photographs taken daily until confluence. We observed that each cell had its individual stable multiplication rate throughout the observation period. This was true for all TSH doses tested (0.625-10 mU/ml). A wide range of doubling times (20 h to almost infinite) in the individual cells was observed. The mean growth velocity of subcloned cell lines was highly reproducible in consecutive passages, although a minority of cells escaped this rule. Cells with either high or low thyroglobulin content occurred in clusters, indicating again that specific traits tend to remain stable in the offspring. We conclude that a highly individual growth program, unrelated to mutation, appears to be switched on at the very moment a cell is generated and that this program is passed on to the majority of the offspring, with a minority of cells acquiring qualities differing from those of their sister cell. Therefore, goiter heterogeneity may be the in vivo amplification of a natural phenomenon occurring in all growing cells. Monoclonal adenomas in vivo and nontransformed immortal cell lines in vitro may represent the far end of the large spectrum of individual growth potency among normal thyrocytes.

Animals↗
PubMed1990

Intercellular propagation of individually programmed growth bursts in FRTL-5 cells. Implications for interpreting growth factor actions.

Five methods are commonly used to quantify FRTL-5 cells' and other thyrocytes' growth in vitro and the impact of growth inhibiting or stimulating maneuvers: Total cell count, mitotic index, DNA measurement, total [3H]thymidine incorporation, and the fraction of [3H]thymidine labeled cells. All of them assess cell growth as though all cells were homogeneous with an identical response to growth factors. We demonstrate here that this assumption is not valid. Rather, some intrinsically growth-prone cells appear to pass a growth signal to neighboring cells so that variably sized colonies of synchronized cells within each cluster growing from monodispersed cells are formed. This is true for FRTL-5 cells growing in vitro in monolayers and in three-dimensional, collagen embedded spheroids. The pattern is the same when cell suspensions or collagen-embedded spheroids are implanted onto nude mice. Patches with alternating high and low growth become particularly prominent in the large tumor-like organoids grown from monodispersed cells in nude mice. The pattern much reminds of similar observations in growing intact thyroids. Since there is no significant correlation between the fraction of [3H]thymidine labeled cells and the size of two- or three-dimensional clusters in any experiment, growth of signal-spreading cells is assumed to occur in leaps and bounds. Growth velocity in each subclone of a cell population depends on the mean interval between bursts of replications and on the number of cells synchronized by cell-to-cell diffusion of the growth signal emanating from one dividing cell. Thus, growth-promoting and growth-inhibiting factors may not only act on the mean interval between successive growth bursts, but they may also change cell-to-cell spreading of growth signals.

Animals↗
PubMed1990

An abnormal splice donor site in one allele of the thyroid peroxidase gene in FRTL5 rat thyroid cells introduces a premature stop codon: association with the absence of functional enzymatic activity.

Low stringency screening of an FRTL5 cDNA library with a human thyroid peroxidase (TPO) cDNA probe yielded two different types of TPO cDNA clones. One type contained the full-length structural gene, but there was an A at the first nucleotide of an intronic splice donor site that leads to alternate splicing, with the retention of part of an intron. This 54-basepair retained intron fragment contains a premature inframe stop codon that would truncate the protein at its carboxyl-terminus by 71% with the loss of enzymatic activity. The second type of TPO cDNA does not contain the retained intron fragment and premature stop codon, but it is not full-length and lacks 580-680 basepairs at its 5' end. However, Northern blot analysis reveals only full-length copies (3.2 kilobases) of TPO mRNA in FRTL5 cells, and this 5' truncation is, therefore, an artifact of library construction. The relative proportions of the two types of TPO mRNA in FRTL5 cells was determined by the polymerase chain reaction, using as template single stranded cDNA generated by reverse transcription of FRTL5 mRNA. Slightly more than half of the TPO mRNA in the FRTL5 cells represented the form with the abnormal splice donor site. The relative proportions of the two TPO mRNA forms was not influenced by TSH stimulation of the FRTL5 cells, and the proportion remained unaltered even after the FRTL5 cells were subcloned by limiting dilution. At the genomic level, we used allele-specific oligonucleotides for the mutant and normal forms of TPO, and found FRTL5 cells to have both normal and abnormal TPO alleles.(ABSTRACT TRUNCATED AT 250 WORDS)

Alleles↗
PubMed1989

[The transformation of Basedow's struma into nodular goiter: a reason for recurrence of hyperthyroidism].

Graves' disease is characterized by a diffuse and homogeneously hyperfunctioning goiter, presumably caused by thyroid stimulating, TSH-receptor directed antibodies (TRAB). However, in many patients the serum concentration of TRAB is in no way parallel to the severity of the clinical course of Graves' hyperthyroidism. In particular, hyperthyroidism may persist or repeatedly relapse over many years despite the absence of high TRAB titers. The present study summarizes the existing evidence that this course of Graves' disease may be due to gradually evolving autonomously growing and functioning micro- or macronodules within the originally diffuse goiter.

Adult↗