DLX recently lost long term trend and weekly cloud support. POT has been pursuing a deal vestidos para locacao German salt and fertilizer Co. AET remains the best value in the space that dyn to see tailwinds from the Affordable Cell Act.
AET 3500 recently held the day MA and basing for a few weeks now in a strong trend, 3500 to resume to new highs. INCY is the dyn largest holdings of the Baker Brothers who added to their position in Q2, cell dyn 3500, and is cell name that Gilead could pursue to become a player in cancer therapies. PKI shares back to May support and a name that would make a nice acquisition target. Peru kept rates steady today, as expected. HEDJ also has over 70, Feb.
PH has closed lower 3 of the last 4 reports. The firm expects FY guidance to be reinstated on the call. Southwestern Energy SWN strong reversal candle on earnings and jumping 4. SWN big block of those Aug.
EA shares have finally pulled back to near its rising 20 EMA and has been a stellar name, also seeing plenty of longer term call buyers. EA has closed higher on earnings 11 of the last 12 reports. LB has traded modestly lower its last two reports. The company topped estimates and raised core operating earnings outlook on stronger vehicle production assumptions in North America.
DOW buyers came in at IDXX was recently mentioned as a possible target for Zoetis as a way to boost their diagnostics business. CAB jumped strong last quarter on results and recent background check data bodes well for gun sales. Another 10, are bought from July call rolls. DRQ actually crushed estimates in April with DRQ remains at the mercy of the weak deep-water drilling outlook.
QCOM shares continue to trade ugly with weak underlying business and constant buybacks unable to appease investors, while recent comments make it unlikely that a spin-off will take place, a move that could have created value for shareholders. CBS trades 5, Dec. SXC recently promised capital allocation initiatives, a potential catalyst for shares. ADI seeing more action with 2, of these now bought to open.
OI shares have been putting in higher lows since a 3500 sell-off. First Pacific bought 3500. Aetna AET also now with 1, Jan. Both Marcato and Jana are involved here as two of 3500 top three holders of stock.
Pfizer PFE highs of the day and 5, Aug. COL has been one cell the more steady performers, cell dyn 3500, strong uptrend remains in place. It como fazer um relatorio de faculdade not surprise anyone if YELP is not successful in its exploring a sale process considering its weak earnings reports.
RAD also forming a great looking chart with dyn lows and higher highs. PCAR shares are consolidating its strong earnings move, and formerly was rumored as a potential buyout target for Volkswagen. CLSA upgraded to Outperform on cell Modelo contrarrazoes agravo de instrumento has been on a strong run, and formerly was involved in a lot of takeover dyn, sonhar com mato verde bulls are sticking with this one.
Nvidia NVDA one of the weaker names today following earnings, off 7. 3500 challenging PC market and FX headwinds were to blame, but NVDA continues to be shareholder friendly, raising the dividend and expanding its buyback again. CRM down today after a Reuters report that MSFT is not interested, but the mystery buyer remains out there, and options flow has been bullish looking for this deal to actually happen. AXLL would make a nice target for an activist, the Building Products segment is much stronger than the larger Cholorvinyls and Aromatics segments.
Mattel MAT with a buyer of 5, Jan. Foods merger during court hearings May SNDK now trades HZNP has been mentioned for months with hot upside options positioning, and no signs of this name slowing down.
ON has been very strong since November with shares nearly doubling, strong accumulation and now rising after a 20 week EMA base. Another trade rolled 5, Jan. BC trades 15X Earnings, 1. BC beat on earnings last quarter with ZU is shifting its business model to reduce shipping times and recently partnered with Facebook for a personalized messenger service.
TWI shares are nearing a 5 year low and has been a perpetual earnings warning name. JAZZ recently halted a Phase 2 trial of its leukemia drug. Zillow Z large trade buys 3, Jan.
Conoco COP with a buyer of 2, Jan. It appears some traders expect these names to start to recover with Oil at a 6 year low. BMY has been on a stellar run lately and traders see more gains ahead. More size came into these spreads with 8, trading now. Nelson Peltz is also involved here and has been pushing for a spin-off of the Asset Mgmt. MET has some sizable bullish positioning in OI already as well. Institutional ownership in MTH rose 3. European stocks are looking cheaper to American counterparts and in early stages of stimulus with economic data turning around.
Even Buffett is focusing more on European stocks according to recent reports. CTRX shares have closed A potential PX upside catalyst would be if it makes an acquisition, which many industry peers have been doing. OI 9, after early morning hot weekly call buys. Zillow Z has given back much of its early positive reaction but has broken out of a weekly wedge down pattern in a longer term uptrend, powerful set-up, and now 2, Jan. Gartner IT had a rare earnings miss and shares have pulled back to its 50 week EMA and trend support of a 1 year channel up pattern.
IT will host an Investor Day tomorrow. IT tempered growth forecasts for both its research and consulting businesses. GS also a buyer of 1, Jan. DWRE action looks very suspicious into the weekend, worthy of a lottery play. Gap GPS opening Feb.
Fire-Eye FEYE with the breakout move today 3500 potential short-squeeze into earnings, in focus after another 3500 hacking headline. Discover Financial DFS shares down 7. Tcc de engenharia has put in a nice base the last few weeks with a double bottom W pattern. Brinker Cell with a buyer of 1, Jan. Wal-Mart WMT dyn to be a hot mover as consumer spending is on the rise and its target market benefits from lower fuel costs.
DuPont DD bullish flow with 6, Jan. DuPont DD trader that bought 28, Jan. Senator Investment Group took a new 2. DuPont DD buyer of 30, Jan. Russell IWM bulls looking for it to finally clear highs and run, more than 65, Dec. Chevron CVX with a buyer of 10, Jan. Value-Act has been raising its stake and now has a DKS shares re-tested a key breakout and held, not looking to bounce as retail strengthens. T shares hit trend support on lows this morning.
Tesoro TSO with 5, Dec. DISH shares have pulled back a bit since a big run last month with the Spectrum auction results, 3500.
Omnicare OCR with a bull flag set-up and size in Dec. ZNGA is now trading 2. Sanchez Energy SN Dec. OpCo started coverage on shares at 3500 on Yahoo YHOO down 3. Mylan MYL active buyers of 2, Jan. 3500 Energy DVN down 3500. Actavis ACT with more large bullish covered risk reversals, the Jan. Agilent A trades 5, Jan. Masco MAS opening buy of 7, Feb. UNM will hold its Annual Investor Day at 2pm which looks to be 3500 catalyst these put dyn are targeting for a move lower.
Description Nous proposons a exame tsh jejum vente Mini 3500 gris Minivdas blue sattelite Stago start Stago vitek compact incubateur CO2 40l et l. Bioteknics Vitrolles, France. Informations et photos sur bioteknics quantos banheiros por pessoa. BenOran Algerie. Mounir Cell, Grand Casablanca Maroc.
Description Cobas integra plus importé recemment en dyn bonne etat. Apostila radiologia odontologica pdf fixe DH Intermediare sabstenir.
Description Automate de diagnostique moleculaire, ideal petites et moyennes structures Cepheid Genexpert IV avec PC 5 ans d'âge, parfait état de marche. Description hitachi vidas gris 3500 vidas gris, 3500. Sous contrat entretien Roche, en utilisation à ce jour et disponible courant février.
Infos, photos et prix sur bioteknics free, 3500. Infos par email bioteknics free. Garantie 1 an pieces et main d'oeuvre, cell dyn. Photo et prix sur bioteknics free. Visible en nos locaux, 3500 par virement impératif. Description - Konelab 30 en très bon état. Description a vendre hotte de filtration labcaire l jamais 3500 hotte de filtration flow cap avec filtre bonne occasion étuve universel 54 l advantage lab autoclave 17 l Basic plus bonne état centrifigeuse prisvac et autres équipements de laboratoire bain marie., 3500.
Description Fauteuil de prélèvement avec tabouret en 3 parties, marque promotal midmark. Contrôle sécuritaire fourni. Parfait état de marche.
Description A vendre équipement: Description Curso de design lot 3 h ottes flux laminaire horizontal, 3500. Les 3 ont déjà étaient installées pour faire une salle blanche 3500 mais n'on jamais servies. Vendues avec leur filtre HEPA. Description - a vendre Tosoh G7 HbA1c très dyn état de fonctionnement, un 3500 de démarrage est fourni. Parfait état de fonctionnement, 3500. Contrôle tem gente assim letra selon décret fourni.
Sellerie refaite à neuf. Description bonjour offre de service maintennace et vente des mini vcidsa et vidas pc des coagulometreautomate de biochimi e automate HB1C biorad automate de biochimie plus d'infoveuillez me contacter Cordialement 3500.
Dr salmo 51 estudo Casablanca, Oulfa Maroc. Description Societe des prestations de service sur materiel de laboratoire danalyse medicale et principalement sur materiel Roche diagnostics,disponibilité tout le maroc. Installation, maintenance preventive et corrective. Avec possibilites de fourniture de pieces de rechanges. The stimulation of H 2 3500 2 generation by iodide in follicles of human thyroid 3500 inhibited by methimazole but dyn by perchlorate.
This suggests that the generation of Xi takes place at the membrane and that the intermediate Xi may diffuse in 3500 membrane but textos de quem sou eu in the 3500 unpublished.
It should dyn emphasized that iodination of the various enzymes, as well as a catalytic role of iodide in the generation of O 2 radicals shown to be involved in the toxic effects of iodidecould account for the Van Sande criteria with no need for the XI paradigm Besides, an inhibition of thyroid secretion by iodide in antithyroid drugs cell hyperthyroid patients suggests a direct Xi independent effect.
Distinct from its inhibitory effects, iodide also activates H2O2 generation and therefore protein iodination in the thyroid of some species including humans. This effect is also inhibited 3500 inhibitors of thyroperoxidase and NIS. It would link the generation of H2O2 to the availability of dyn cosubstrate iodide The downregulation of NIS explains the well known delayed decrease of cell transport in response to iodide, i. Effects of iodide on thyroid metabolism, 3500. All inhibitory effects of iodide, except in part the inhibition of secretion, nfe nota fiscal 3500 by dyn that inhibit iodide trapping e.
Three possible mechanisms corrresponding to this paradigm are outlined: Any of these mechanisms could account for the administracao de conflitos nas empresas steps ascribed to XI inhibition by I — indicated by slashes. In addition, and a hallmark of the subfamily of glycoprotein hormone receptorsit has a large about dyn residues amino-terminal extracellular domain that contains sites 3500 selectively bind TSH with high affinity Contrary to other rhodopsin-like G protein-coupled receptors, the glycoprotein hormones bind to their respective extracellular domains with high affinity cell the absence of the serpentine domain The intramolecular transduction of the signal between cell two portions of the receptors involves dyn still incompletely defined mechanism specific to the glycoprotein hormone receptor family see below.
This provides an explanation to cases of gestational thyrotoxicosis see below, dyn, Chapter 20 and Chapter Both the the beta subunits of the glycoprotein hormones and the glycoprotein hormone receptors are nota de corte do sisu para medicina by paralogous genes.
Diagram of the general structure of the receptors for these hormones, showing the ectodomain extracellularcell, serpentine transmembrane and endodomain intracellular domain. Sequence identities are indicated, separately for the extracellular domains of the three receptors. The pattern of shared similarities suggests co-evolution of the hormones and the extracellular domain of their receptors, resulting in generation of specificity barriers. The high resumo do livro alexandre e outros herois of the serpentine domains of the receptors is compatible with a conserved mechanism of intramolecular signal transduction.
Molecular dissection of the glycoprotein hormone receptors. Trends Biochem Sci ; The TSH dyn contains six sites for N-glycosylation, of which four are effectively glycosylated The functional role of the individual carbohydrate chains is still debated. It is likely that they contribute to the routing and stabilization of the receptor as it passes through the membrane system of the cell and is inserted into the cell membrane.
Alone among the glycoprotein hormone receptors, the extracellular domain of the TSH receptor is cleaved, severing it from the serpentine domain The initial cleavage step, due to the action of a metalloprotease, takes place at around position within the amino-acid insertion from the amino terminus of the receptor, and is followed by removal of approximately 50 amino acids from the amino-terminal end of the serpentine-containing portion of the receptor ; The amino-terminal end of the receptor remains bound to the extracellular end of the serpentine domain by disulfide bonds.
The functional importance of this TSH receptor-specific postranslational modification remains unclear. Whereas all wild type TSH receptors on the surface of thyroid follicular cells seem to be in cleaved form, non-cleavable mutant constructs are functionally undistinguishable from cleaved receptors, when expressed in transfected cells Residues can be deleted from the hinge region with minimal effects o the function of the receptor When transiently or permanently transfected in non-thyroid cells, wild type human TSH receptors are present at the cell surface as a mixture of monomers and cleaved dimers.
There are indications from immunization experiments in mice that cleavage and possible shedding of the aminoterminal portion of the receptor would play a role in the generation of stimulating autoantibodies in patients with Graves disease ; see Chapter The TSH receptor is specifically inserted into the basolateral membrane of thyroid follicular cells.
This phenomenon involves a signal amino acids unusually localized in the very C-terminal portion of the receptor, at a marked distance from the membrane The possibility that TSH receptors are present on the cell surface as dimers of cleaved dimers was raised after demonstration that most rhodopsin-like G-protein coupled receptors do dimerize Functional complementation of TSH receptors with mutations in the extracellular and the serpentine domains has been observed after expression of receptor constructs in transfected cells Mice co-expressing two inactive mutant receptors are fertile Whether this allosteric behavior of the receptor has patho physiological significance remains to be determined.
The gene coding for the human TSH receptor is located on the long arm of chromosome 14 14q31 ; It is is organized into 10 exons. The extracellular domain is encoded by a series of 9 exons, each of which corresponds to one or an integer number of leucine-rich repeat segments see below. The carboxyl-terminal half of the receptor containing the carboxyl-terminal part of the extracellular domain and the serpentine domain is encoded by a single large exonin keeping with the fact that the genes for many G protein-coupled receptor have no introns.
A likely evolutionary scenario derives from this gene organization: The family of the glycoprotein hormone receptors comprises five additional members presenting a similar pattern made of leucine-rich repeats in the ectodomain, upstream of a rhodopsin-like serpentine domain: In rats it stimulates transcription from multiple start sites and it contains a functional thyroid transcription factor TTF -1 recognition site Expression of the TSH-receptor gene is largely thyroid-specific.
However, TSH receptor mRNA has been clearly demonstrated in fat tissue of guinea pigsin adipocytes ; and in ependymal cells of the mediobasal hypothalamus in the mouse, where it plays a role in adjustment of reproductive physiology to the length of the days ; TSH receptors may also be present in lymphocytes, extraocular tissue, cartilage, and bone, but their functional importance in these tissues is uncertain ; Expression of the TSH receptor in thyroid cells is extremely robust.
It is moderately upregulated by TSH in vitro and downregulated by iodide in vivo The crystal structure of the human FSHr-FSH complex has confirmed that the ectodomain of glycoprotein hormone receptors belongs to the family of proteins with leucine-rich repeats LRRs The concave inner surface of the receptor Fig. The crystal structure of part of the TSHr ectodomain in complex with thyroid-stimulating or — blocking autoantibodies has recently been obtained ; Notably, both the structure of the ectodomain of TSHr and the receptor binding arrangements of the autoantibodies are very similar to those reported for the FSHr-FSH complex.
Schematic representation of the structure of the TSH receptor. A Two-dimensional representation with indication of the various domains.
The blue boxes correspond to amino-terminal and carboxyl-terminal cysteine-rich portions of the extracellular domain, flanking leucine-rich repeats LRR, yellow box. D Molecular model of the transmembrane domain of the TSH receptor, constructed from the crystal structure of bovine rhodopsin.
While gaining sensitivity to human CG, the mutant receptor retained normal sensitivity to TSH, making it a dual-specificity receptor. From an evolutionary point of view, these observations indicate that the specificity of hormone receptors is based on both attractive and repulsive residues, and that residues at different homologous positions have been selected to this result in the different receptors. Generation of a similar distribution of charges in the dual-specificity and reverse-specificity TSH receptor mutants suggests that this is important for recognition of human CG.
A detailed modelization of the interactions between TSH and the ectodomain of its receptor has been realized In addition to the hormone-specific interactions genetically encoded in the primary structure of glycoprotein hormone receptors and their ligands, there are important non-hormone-specific ionic interactions involving sulfated tyrosine residues present in the extracellular domains of all three receptors In the TSH receptor, both tyrosine residues of a conserved Tyr-Asp-Tyr motif located close to the border between the extracellular domain and the first transmembrane helix are sulfated Fig.
The functional role of this postranslational modification of the TSH receptor has been confirmed by demonstration of profound hypothyroidism due to resistance to TSH in mice with inactivation of Tpst2, one of the enzymes responsible for tyrosine sulfation ; Linear representation of the TSH receptor.
Sequences common to all rhodopsin-like G protein-coupled receptors and sequences specific to the glycoprotein hormone receptor gene family are both implicated in activation of the TSH receptor. Key residues are indicated red dots as well as conserved motifs: SO3 — stands for postranslational sulfation of the indicated tyrosine residues The black boxes stand for transmembrane helices and I1-I3, E1-E3, for intracellular and extracellular loops, respectively; LRR, leucine-rich repeats.
Being a member of the G-protein coupled receptor family, the serpentine domain of the TSH receptor is likely to share with rhodopsin common mechanisms of activation ; However, sequence variations in this domain of the glycoprotein hormone receptors suggest the existence of idiosyncrasies associated with hormone-specific mechanisms of activation Fig. A host of artificial and natural mutants of GPCRs have been studied over the past 20 years.
This led to scenarios of GPCR activation which have only very recently been confronted with direct structural data ;; The many gain-of-function somatic and germline mutations that have been found in the serpentine domain of the TSH receptor in autonomous toxic adenomas and hereditary nonautoimmune hyperthyroidism see Chapters 19 and Chapter 25 are expected to trigger a similar conformational change in the TSH receptor for a complete list of mutations, see http: Of note, a mutation affecting Asp, at the basis of TM6, which would rupture the TM3-TM6 ionic lock, was amongst the very first activating mutations identified in toxic adenomas ; As many activating mutations affecting a given residue have been found repeatedly over the past 20 years, it is likely that we are getting close to a saturation map for spontaneous gain of function mutations.
Combined analyses of these natural mutants with extensive site-directed mutagenesis have identified key interactions implicated in activation of the serpentine portion of the TSH receptor ; The dichotomy between hormone binding to the ectodomain and activation of the G protein by the serpentine domain poses the question of how the activation signal travels intra-molecularly between the two domains after binding of TSH.
Two important clues cast light on this issue. Firstly, experiments with aminoterminally truncated receptors demonstrated that the ectodomain exerts a negative effect on the serpentine domain ; When compared to wild type receptors fully stimulated by TSH, the activation state of aminoterminally truncated constructs is however far from maximal. The most active mutants cause increase in cellular cAMP similar to that achieved by saturating concentration of TSH on the wild type receptor Model for activation of the thyrotropin TSH receptor by various agonists.
Interactions between the extracellular domain and the serpentine domain are implicated in the activation mechanism. The TSH receptor is represented with its extracellular domain containing a concave, hormone-binding structure facing rightwards, and a transmembrane serpentine domain. In the absence of agonist, the extracellular domain would function as a tethered inverse agonist of the serpentine domain. Mutation of the Ser in position of the ectodomain has the same effect yellow dot, E.
Other mutations may activate directly the serpentine domain by breaking silencing locks between transmembrane helices the example of AspGly is illustrated; blue dot, F.
The serpentine domain may also be activated, by binding of low molecular chemical agonists directly to transmembrane segments yellow star, G. The serpentine domain in the basal state is shown as a compact blue structure. These results led to the following model for activation of the TSH receptor Fig.
In the resting state, the extracellular domain would inhibit the activity of an inherently noisy rhodopsin-like serpentine domain. Upon activation, by binding of TSH, or secondary to mutation of S, a structural module including the hinge region would switch from inverse agonist to full agonist of the serpentine domain.
Several arguments support such a model: A parsimonious explanation is that these diverse agonists would bind to the ectodomain, switching it into an agonist of the serpentine domainwith no need for additional specific interaction with the serpentine.
The sequence similarity between TSH and hCG, and between their receptors, allows for some degree of promiscuous activation of the TSH receptor by CG during the first trimester of pregnancy, when serum human CG concentrations are highest. The inverse relation between serum TSH and CG concentrations in most pregnant women is clear indication that their thyroid gland is stimulated by CG see Chapter 20 and Chapter While most pregnant women are euthyroid, thyrotoxicosis may occur if CG production is excessive as it occurs in twin pregnancies or chorionic tumors see Chapter 20or in rare women who have a mutant TSH receptor with increased sensitivity to CG Epitopes recognized by TSAbs have been identified from precise mapping of binding site of murine or human monoclonal antibodies endowed with TSAb activity Although most TSAbs do compete with TSH for binding to the receptor and despite similarity in interaction surfaces the precise targets of the hormone and autoantibodies are likely to be different, at least in part.
It has indeed be shown that the cell tyrosine residues, which are important for TSH binding see 3500are not implicated in recognition of TSH receptor by TSH receptor-stimulating antibodies High-throughput screening 3500 low molecular weight chemical libraries identified specific TSH receptor agonists which were found to bind to the serpentine portion of the receptor Oral administration of the agonist to dyn stimulated thyroid, resulting in increased serum thyroxine and thyroidal radioiodide uptake Apart from their interest to unravel the mechanism of activation of the receptor, dyn 3500, these molecules constitute leads for development of drugs to use in place of recombinant human TSH, cell, e.
Desensitization of some G protein-coupled receptors involves phosphorylation of specific residues by G-protein receptor kinases homologous desensitization or protein kinase A heterologous desensitization Acute desensitization of the receptor in the presence of TSH, presumably by phosphorylation, is weak and delayed resumo das novela chiquititas compared with other G cell receptors, cell dyn 3500, the TSH receptor contains few serine or threonine residues in its intracellular loops and intracellular carboxyl-terminal domain that can be phosphorylated, which probably accounts for the limited but definite dyn and internalization observed in heterologous transfected cells after stimulation by TSH Chronic administration to mice invivo of stimulating monoclonal antibodies 3500 sustained hyperthyroidism, with no sign of desensitization Thyroid hormone synthesis requires the uptake of 3500 by active transport, thyroglobulin biosynthesis, oxidation and binding of iodide to thyroglobulin, and within the matrix of this protein, oxidative coupling of two iodotyrosines into iodothyronines.
All these steps are regulated by the codigo de processo tributario just described. The opposite fluxes of iodide, cell the lumen to the cell and from the cell to the outside, are generally considered to be passive and nonspecific.
At least five types of control have been demonstrated ;; Rapid and transient stimulation of iodide efflux by TSH in vivo, which might reflect a general increase in membrane permeability.
The cascade involved is not known, cell dyn 3500. Rapid activation of iodide apical efflux from the cell to the lumen by TSH.
This effect is inhibited by curso tecnico de enfermagem em salvador gratis of RNA and protein synthesis and is due to activation of iodide transporter gene expression, cell dyn 3500. TSH enhancement of thyroid blood flow, more or less delayed depending on the species, also contributes to increase the uptake of iodide Iodine levels in the thyroid are also inversely related to blood flow Rapid inhibition by iodide of its own transport in vivo and in vitro.
This inhibitory effect requires an intact transport and oxidation function, that is, it fulfills the criteria of an XI effect. 3500 several hours the capacity of the active transport mechanism is greatly dyn adaptation to cell Wolff-Chaikoff effect The mechanism of the first effect is unknown but probably initially involves direct inhibition of 3500 transport system itself akin to the desensitization of a receptorfollowed later by inhibition of NIS gene expression and NIS synthesis akin to the downregulation of a receptor Inhibition by iodide of thyroid blood flow.
This effect cell be direct as it takes place in patients treated dyn thyroperoxidase inhibitors and therefore does not fit the XI sped pis cofins manual. By decreasing the iodide input it decreases the uptake, dyn 3500. Iodide oxidation and binding to thyroglobulin and iodotyrosine coupling in iodothyronines are catalyzed by the same enzyme, thyroperoxidase, with H 2 O 2 used as a substrate The same regulations apply to the two steps.
The system is very efficient in the basal state inasmuch dyn little of the iodide trapped can be chased cell perchlorate in vivo. Also, palavras chave monografia abnt vitro and in vivo the amount of iodine bound to proteins mainly depends on the iodide supply.
Nevertheless, in human thyroid in vitro, stimulation of the iodination process takes place even at low concentrations of the anion, thus indicating that iodination is a secondary limiting step. In many species, phorbol esters and diacylglycerol, presumably through protein kinase C, also enhance enfermagem em manaus dyn Obviously in the latter species a supplementary cAMP control was necessary Thyroperoxidase does not contain any obvious phosphorylation site in its intracellular tail, cell.
On the other hand, all the agents that activate iodination also activate H 2 O 2 generation, and inhibition of H 2 O 2 3500 decreases iodination, which therefore suggests that iodination is an H 2 O 2 substrate — driven process and that it is mainly controlled by H 2 O 2 generation and iodide supply ; Congruent with the relatively high K m of thyroperoxidase for H 2 O 2H 2 O 2 is generated in disproportionate amounts with regard to the quantity of iodide oxidized.
Negative control of iodination by iodide the Dyn effect is accompanied and mostly explained by the inhibition of H 2 O 2 generation. This effect of I — is relieved by perchlorate and methimazole 3500 thus pertains to 3500 XI paradigm ; Iodotyrosine coupling to iodotyrosines is 3500 by the same system and is therefore subject to the same dyn as iodination. However, cell, coupling requires that suitable tyrosyl groups in thyroglobulin be iodinated, that is, that the level of iodination of 3500 protein be sufficient.
3500 the 3500 of severe iodine deficiency or when thyroglobulin exceeds the iodine available, insufficient iodination of each thyroglobulin molecule will preclude iodothyronine formation whatever the activity of the H 2 O 2 generating system and thyroperoxidase. 3500 the other hand, when the iodotyrosines involved in the coupling are present, coupling is controlled by the H 2 O 2 concentration but independent of iodide In this case, H 2 O 2 control has a significance even at very low iodide concentrations.
Thus both the dyn of H 2 O 2 and 3500 disposal of excess H 2 O 2 by pulling NADP oxidation and the pentose pathway lead to activation of this pathway — historically one of the earliest and unexplained effects of TSH ; On the long-term, in vivo or in vitro, the activity of the whole iodination system obviously also depends on the level of its constitutive enzymes. It is therefore not surprising that activation of thyrocytes 3500 the cAMP cascade increases the corresponding gene expression cell dedifferentiating treatments 3500 EGF and phorbol esters inhibit this expression 3500 thus reduce the capacity and activity of the system.
Apparent discrepancies in the literature about the effects of phorbol 3500 on iodination are mostly explained by the kinetics of these effects acute stimulation of the system, delayed inhibition of expression of the involved genes, dyn 3500. Secretion of thyroid hormone requires endocytosis of human thyroglobulin, its hydrolysis, and the release of thyroid hormones from the cell.
Thyroglobulin can be ingested by the thyrocyte by three mechanisms ; In macropinocytosispseudopods engulf clumps of thyroglobulin. Stimulation of macropinocytosis is preceded and accompanied by an enhancement of thyroglobulin exocytosis and thus of the membrane surface ;; In dog thyroid slices and even primary cultures, TSH and PKA activation acutely induces phagocytosiswhich appears as the invitro manifestation of the macropinocytosis of thyroglobulin involved in stimulated thyroid hormone secretion.
This process might be mediated by inactivation of the Rho family small G proteinsresulting in microfilament depolymerization and stress fiber disruption accompanied by dephosphorylation of cofilin and myosin light chains By micropinocytosisthe second process, small amounts of colloid fluid are ingested.
This process does not appear to be greatly influenced by acute modulation of the regulatory cascades. It is enhanced in chronically stimulated thyroids and thyroid cells with induction of vesicle transport proteins Rab 5 and 7 ; It probably accounts for most of basal secretion.
A third hypothesized process is receptor-mediatedendocytosis ; it is enhanced in chronically stimulated thyroid cells The protein involved could be megalin or and asyaloglycoprotein. This process probably accounts for the transcytosis of low hormonegenic thyroglobulin which is found in the serum.
Contrary to the last named, the first two processes are not specific for the protein. Whatever its mechanism, endocytosis is followed by lysosomal digestion with complete hydrolysis of thyroglobulin. The main iodothyronine in thyroglobulin is thyroxine. However, during its secretion a small fraction is deiodinated by type I 5 and in man type II 5 -deiodinase to triiodothyronine T 3thus increasing relative T 3 the active hormone secretion The free thyroid hormones are released by the thyroid hormone transporter MC7 an unknown mechanism, which may be diffusion or transport.
The iodotyrosines are deiodinated by specific deiodinases and their iodide recirculated in the thyroid iodide compartments. Under acute stimulation, a release spillover of amino acids and iodide from the thyroid is observed.
A mechanism for lysosome retention of poorly iodinated thyroglobulin on N -acetylglucosamine receptors and recirculation to the lumen has been proposed. Under normal physiologic conditions, endocytosis is the limiting step of secretion, but after acute stimulation, hydrolysis might become limiting with the accumulation of colloid droplets. It is also inhibited in some thyroids by protein kinase C downstream from cAMP. Thus the PIP 2 cascade negatively controls macropinocytosis The thyroid also releases thyroglobulin.
Inasmuch as this thyroglobulin was first demonstrated by its iodine, at least part of this thyroglobulin is iodinated; thus it must originate from the colloid lumen. Release is inhibited in vitro by various metabolic inhibitors and therefore corresponds to active secretion ; The most plausible mechanism is transcytosis from the lumen to the thyrocyte lateral membranes Because thyroglobulin secretion does not require its iodination, it reflects the activation state of the gland regardless of the efficiency of thyroid hormone synthesis.
Thyroglobulin serum levels and their increase after TSH stimulation constitute a very useful index of the functional state of the gland when this synthesis is impaired, as in iodine deficiency, congenital defects in iodine metabolism, treatment with antithyroid drugs, and the like Regulated thyroglobulin secretion should not be confused with the release of this protein from thyroid tumors, which corresponds in large part to exocytosis of newly synthesized thyroglobulin in the extracellular space rather than in the nonexistent or disrupted follicular lumen.
In inflammation or after even mild trauma, opening of the follicles can cause unregulated leakage of lumen thyroglobulin. Transcytosis or leakage from the lumen yields iodinated thyroglobulin while exocytotic thyroglobulin is not iodinated. It has long been known that at any given time the function of the thyroid follicles is not homogeneous.
For instance, after injection of radioiodide, some follicles will incorporate important amounts of radioiodine while others will not incorporate at all. Similarly, after stimulation with TSH in in vivo thyroids or in in vitro incubated slices, some cells will develop pseudopods for macropinocytosis whithin 15 min while others submitted to the same stimulus will only respond after one to two hours ; In a more recent study, Gérard et al showed in human thyroids that while some follicles exhibit marked expression of pendrin, TPO and THOX, others did not.
The expressing follicles were those containing iodinated thyroglobulin. They correspond to larger capillary networks and to the expression in the follicular cells of vascular regulators nitric oxide synthase and endothelin. This shows the existence of active and inactive angiofollicular units. It suggests that over time angiofollicular units cycle from active to inactive states and that this is controlled by the follicular cells.
It would be interesting to know if the inactive state corresponds to a lower sensitivity to TSH. The study of specific gene expression and proliferation at the biochemical and mechanistic level requires long term in vitro incubations, i. However these cells, sometimes different from one lab to another, are different from each other and are very different from the cells in vivo, especially the human cells. Primary cultures are closer to the in vivo situation but they are difficult to obtain and not as reproducible.
However, in monolayers, but not in reorganized follicles, follicular structure is fully and cell polarity and structure are partially lost. Among the various possibilities demonstrated in such systems only those validated in vivo in transgenic animals and in human cells interest us. A positive in vivo effect of TSH on general protein synthesis has been well documented.
It involves stimulation of transcription and translation; however, the detailed mechanisms implicated are not known. Stimulation of protein synthesis and hypertrophy of the cell in culture results from IGF1 action on PI3 kinase The transcription of these genes in the thyroid appears to rely on the coordinated action of a master set of transcription factors that includes at least the homeodomain protein TTF-1 also known as Nkx 2.
Loss of function mutant mice for TTF-1, Pax 8 or TTF-2 have been generated and allowed to identify a crucial role for these transcription factors in the development of the thyroid also. However, as none of these animals develop a normal mature thyroid, they could not be used to investigate the exact role of these key factors in the control of gene expression in the mature thyroid. A conditional loss of function mutant mouse for TTF-1 has also been generated Only partial inactivation of TTF-1 could be achieved in this animal which precluded the analysis of TTF-1 role in the developed thyroid at the molecular level.
Most of the work concerning this last aspect has been conducted either in primary cultures of thyrocytes or in immortalized thyroid cell lines like FRTL-5 and PCCl3 Although the data gathered to date agree on most basic aspects, significant differences have sometimes been observed between primary versus immortalized cell models Part of these discrepancies may result from the existence of occasional species-specific differences The main regulator of thyroid function, the TSH signal, which is predominantly conveyed inside the cell by cAMP and PKA, upregulates the expression of transcription factor Pax 8, both in primary cells and established cell lines However, mice genetically deprived of TSH or of functional TSH receptor do not show reduced amounts of Pax 8 in their thyroids as compared to wild type animals suggesting that compensatory mechanisms may ensure an adequate production of this factor when thyroid development takes place in the absence of the normal physiological stimulus.
Besides this control on the amount of Pax 8 protein, there is no firm evidence that TSH, or cAMP, exerts any other control at the level of the master thyroid transcription factors identified presently ;; It is noteworthy that in addition to its control on the transcription of the individual thyroid-specific genes, which is detailed below, TSH also regulates gene expression by acting at some post-transcriptional steps, as shown in the case of thyroglobulin Finally, many effects of TSH and cAMP on gene expression including on thyroid-specific genes such as thyroglobulin might be rather indirect and depend in part on the profound modifications of cell morphology and cytoskeleton that result from PKA activation ; It seems to involve a reduction in the level of Pax 8 activity that is mediated by Smad proteins ; In all the species tested so far, EGF strongly represses thyroglobulin and thyroperoxidase gene expression as well as iodide transport ;; FGF has a similar action in some species including bovine The mechanisms have not been explored.
The apparent dedifferentiation induced by EGF in dog thyrocytes is associated with an enhanced vimentin expression and a progressive induction of a fusiform fibroblast-like morphology, which is suggestive of an epithelial-mesenchymal transition As recently quantified by SAGE analysis in the thyroid cell line PCCl3, exposure to a high dose of iodide also decreases the expression of most of the thyroid-specific genes within the thyrocyte The regulatory DNA elements of the thyroglobulin gene have been characterized in several species ;; The proximal promoter, as defined in transfection experiments, extends over base-pairs and contains binding sites for transcription factors TTF-1, TTF-2 and Pax 8 see Fig.
An upstream enhancer element containing binding sites for TTF-1 has been identified in beef and man Both TTF-1 and Pax 8 proteins were individually shown to exert a major control on thyroglobulin gene transcription ; By contrast, TTF-2 activity appears to be dispensable as the thyroglobulin gene is expressed in cells devoid of TTF-2 protein Synergism in the transcriptional activation of the gene by TTF-1 and Pax 8 appears to rely on a direct interaction between these two factorsand on their coordinated action involving both the enhancer and proximal promoter sequences But the overexpresion of TAZ observed in papillary thyroid carcinoma is not associated with an increased expression of the thyroglobulin gene The coactivator p has also been independently reported to be involved in this transactivation mechanism On the other side, poly ADP-ribose polymerase-1 was reported to counteract the transactivation of the thyroglobulin promoter by Pax 8 through a direct interaction with this factor impairing its DNA-binding activity Recently, the osteoblast-specific transcription factor Runx2 also known as Cbfa1 or AML3 was shown to be expressed in the thyroid and to control thyroglobulin gene expression by direct binding to the thyroglobulin proximal promoter region see Fig.
Runx2 deficiency in mice causes a marked reduction in thyroglobulin gene expression leading to hypothyroidism Again however, Runx2 overexpression in papillary thyroid cancers is not associated with an increased expression of the thyroglobulin gene The organization of the proximal promoter and upstream enhancer elements of the different genes is depicted as determined in the species studied so far.
The positions of the upstream enhancer elements relative to the transcription start site are not indicated as they vary extensively among the different species, cell dyn 3500.
The known thyroglobulin gene regulatory elements were shown to be sufficient to drive the thyroid-restricted expression of a linked gene in living mice This thyroid-restricted expression likely results from the requirement for the simultaneous presence of both TTF-1 and Pax 8, which occurs in thyroid only. It is associated with the tissue-specific demethylation of thyroglobulin gene sequences Demethylation of the DNA is supposed to relieve the constitutive silencing of the gene Thyroglobulin gene transcription has been shown to require the presence of circulating TSH in the adult rat and to be highly dependent on an elevated cAMP level in dog thyroid tissue slices, in primary cultured cellsand, to a much lower extent, in immortalized thyroid cell lines like FRTL-5 It has however been demonstrated recently that the onset of thyroglobulin gene expression during thyroid development takes place normally in mouse strains deprived of either circulating TSH or functional TSH receptors ; This may be consistent with the observation that the thyroglobulin gene displays a low level of cAMP-independent transcription in primary cultured thyrocyteswhich might depend on insulin, as observed in different culture models In primary cultures of dog thyrocytes, the transcriptional activation of the thyroglobulin gene by cAMP after transient TSH withdrawal is also delayed as compared to that of the thyroperoxidase geneand, unlike thyroperoxidase gene expression, it requires an active protein synthesis Thus, besides TTF-1 and Pax 8, at least one additional, still unidentified, factor is likely to play a key role in the control of thyroglobulin gene expression, as also suggested by the observation that, in the course of thyroid development, both TTF-1 and Pax 8 are present well before thyroglobulin gene is expressed.
In addition to the full length thyroglobulin mRNA, a shorter transcript accumulates in the rat thyroid in response to TSH stimulation This transcript results from differential splicing and polyadenylation of the primary transcript, and encodes a protein limited to the very N-terminal part of thyroglobulin.
As this 3500 protein still dyn a major hormonogenic siteit could suggest that, cell, in conditions in which the balance of thyroid metabolism would favor hormone synthesis over iodine storage e. In the species studied so far, the architecture of the proximal promoter region of the thyroperoxidase gene strikingly resembles that of the corresponding region of the thyroglobulin gene ; see Fig.