A novel mutation (E333D) in the thyroid hormone beta receptor causing resistance to thyroid hormone syndrome.

Resistance to thyroid hormone (RTH) is an inherited syndrome characterized by elevated serum thyroid hormones (TH), failure to suppress pituitary thyroid stimulating hormone (TSH) secretion, and variable peripheral tissue responsiveness to TH. The disorder is associated with diverse mutations in the thyroid hormone beta receptor (TRbeta). Here, we report a novel natural RTH mutation (E333D) located in the large carboxy-terminal ligand binding domain of TRbeta. The mutation was identified in a 22-year-old French woman coming to medical attention because of an increasing overweight. Biochemical tests showed elevated free thyroxine (T4: 20.8 pg/ml (normal, 8.5-18)) and triiodothyronine (T3: 5.7 pg/ml (normal, 1.4-4)) in the serum, together with an inappropriately nonsuppressed TSH level of 4.7 mU/ml (normal, 0.4-4). Her father and her brother's serum tests also showed biochemical abnormalities consistent with RTH. Direct sequencing of the TRbeta gene revealed a heterozygous transition 1284A>C in exon 9 resulting in substitution of glutamic acid 333 by aspartic acid residue (E333D). Further functional analyses of the novel TRbeta mutant were conducted. We found that the E333D mutation neither significantly affected the affinity of the receptor for T3 nor modified heterodimer formation with retinoid X receptor (RXR) when bound to DNA. However, in transient transfection assays, the E333D TRbeta mutant exhibited impaired transcriptional regulation on two distinct positively regulated thyroid response elements (F2- and DR4-TREs) as well as on the negatively regulated human TSHalpha promoter. Moreover, a dominant inhibition of the wild-type TRbeta counterpart transactivation function was observed on both a positive (F2-TRE) and a negative (TSHalpha) promoter. These results strongly suggest that the E333D TRbeta mutation is responsible for the RTH phenotype in the proposita's family.

Triiodothyronine nuclear receptor and the role of non-histone protein factors in in vitro triiodothyronine binding.

The rat liver triiodothyronine (T3) nuclear receptor rapidly looses, after a partial purification from the nuclear extract, its ability to bind T3. We previously reported that histones, in the presence of DNA, could protect against inactivation enhancing the T3 binding site concentration and maintaining the high affinity for T3. A nuclear fraction discarded during the receptor purification (fraction A) was also found able to restore T3 binding and was analyzed. As histones + DNA, fraction A stabilized the T3 binding site from irreversible inactivation during incubation with T3, increasing its concentration while keeping the same high affinity for T3. It was active even at relatively high receptor concentration, appeared slightly more active than histones (+ DNA) in the same protein concentration range (up to 50-fold increment of T3 binding at the optimal concentration of 25 micrograms/ml) and was unaffected or slightly inhibited by DNA. Other proteins (ovalbumin, soybean trypsin inhibitor, RNAase) and rat liver cytosol were several times less effective, suggesting a major role of some nuclear constituents. The active factors in fraction A essentially belong to non-histone nuclear proteins. Fraction A was found heterogeneous regarding the molecular size and pHi of the active factors, the existence of subfractions more active on a protein concentration basis being suggested but not yet clearly evidenced. Efficient in vitro T3 binding to the isolated T3 nuclear receptor thus depends on the presence of several different nuclear constituents, histones + DNA or some non-histone proteins. Whether interactions with these constituents could modulate T3 binding within the nucleus remains to be elucidated.

Triiodothyronine nuclear receptor. Role of histones and DNA in hormone binding.

The triiodothyronine (T3) nuclear receptor was previously shown to lose rapidly its high affinity hormone-binding property after a partial purification from the nuclear extract. It was then found that histones + DNA added to the incubation medium with labeled T3 could restore, at least in part, the high affinity T3 binding. We now demonstrate that DNA alone increases the high affinity T3 binding site concentration moderately, and only at low ionic strength where it can bind to the receptor. Total histones and all histone fractions studied (total core histones, F2a, H2B, H3, H4, H1) specifically increase, at low concentrations, the level of T3 binding; but higher concentrations of some individualized histones, particularly arginine-rich histones, have an inhibitory effect. DNA, or several other polynucleotides, in the presence of histones increase the stimulating histone effect and reverse the inhibitory effect into a true activation. Histones increase the number of T3 binding sites but decrease the affinity for T3; addition of DNA restores the high affinity for T3 and stabilizes the T3-receptor complexes. Thus, some of the histone molecules could play a role in the maintenance of the T3 binding site, but multiple interactions between histones or with DNA seem necessary to impair the negative effect exerted by other parts of the histone molecules. Whether these positive and negative effects of histones on the T3 binding site are of biological relevance in the regulation of T3 binding to its receptor remains to be determined.

The role of triiodothyronine in the regulation of synthesis rate and translatable mRNA level of fatty acid synthetase in a preadipocyte cell line.

Triiodothyronine (T3) effects on the activity, rate of synthesis and mRNA content of the key lipogenic enzyme, fatty acid synthetase, were studied in differentiating ob17 preadipocytes cloned from ob/ob mouse epididymal adipose tissue. During differentiation in the presence of insulin, a 6-10-fold increase in both fatty acid synthetase specific activity and synthesis rate were reproducibly observed and occurred concomitantly. The relative synthesis rate exhibited a progressive elevation from 0.5% at confluence to a maximum level of 2% in the presence of insulin. The rate of the enzyme degradation determined by pulse-chase experiments was similar in differentiating cells and insulin-untreated cells of the same age (t 1/2, 40-42 h). Furthermore, the increase in the enzyme synthesis rate was preceded by a progressively elevating amount of mRNA encoding for this protein as detected by translation in a reticulocyte lysate cell-free system. It is thus suggested that the increment in total and neosynthesized fatty acid synthetase in essentially due to an increased enzyme synthesis, reflecting an increased relative content of its specific mRNA. T3 included at a physiological concentration (1.5 nM) in the culture medium enhanced significantly both enzyme synthesis and its specific mRNA. The most important T3 effect was an acceleration of both processes, a stimulation of the mRNA level being detected as early as day 3 post-confluence and maximum at day 5 when the effect on the synthetase synthesis rate and activity began to be enhanced. This suggests that T3 would mainly affect fatty acid synthetase as a pretranslational level.

Increase of adipose differentiation by hypolipidemic fibrate drugs in Ob 17 preadipocytes: requirement for thyroid hormones.

The action of hypolipidemic fibrate drugs (HFD) (clofibrate, bezafibrate, fenofibrate) was studied in relation to thyroid hormone (TH) action in the TH-sensitive Ob 17 preadipocyte cells which require an early presence of TH for terminal differentiation. HFD markedly amplified the adipose differentiation and the development of several lipogenic enzymes, thus accelerating their appearance after cell growth arrest. This amplifying action could be obtained whatever the time of drug addition to the cells and required the continuous presence of the drug. HFD action was strictly dependent on the presence of TH. Within the active concentration range (0.01-0.25 mM) in serum-containing medium, HFD moderately down-modulated the nuclear TH receptor level (and c-erb alpha mRNA abundance), this being additive to the known maximal but partial down-regulation provoked by TH. The results strengthen the TH obligatory role for Ob 17 cell differentiation and give arguments against a TH-like role of HFD. In this cell line, HFD mainly behave as amplifiers for the expression of lipogenic phenotypes in already committed cells.

The effect of triiodothyronine on fatty acid synthetase activity and content in differentiating ob17 preadipocytes.

The effect of triiodothyronine on the activity and amount of the key lipogenic enzyme fatty acid synthetase was studied in differentiating preadipocyte cells (ob17) isolated from ob/ob mouse epididymal fat pad. In the presence of physiological concentrations of insulin, the acquisition of adipose morphology was accompanied by a parallel increase (10--15-fold) in synthetase specific activity and radioimmunoassayable amount relative to soluble cellular proteins. Inclusion of T3 at confluence significantly enhanced synthetase activity and content, with a maximum of 1.5--2-fold above controls at the physiological 1.5 nM concentration, whether insulin is present or not. During adipose conversion, T3 increased the development of enzyme activity and after a longer lag period, the accumulation of the synthetase. Our results suggest that the stimulating effect of T3 upon synthetase activity could involve as a first step the activation of preexisting inactive synthetase molecules and as a second one an increased accumulation of activable synthetase. After longer culture periods, inactive radioimmunoassayable synthetase accumulated.

Identification of second lipolysis activating protein from scorpion Buthus occitanus tunetanus.

Besides the previously described LVP1, a second protein, LVP2, inducing a lipolytic response in adipose cells, was purified from scorpion Buthus occitanus tunetanus venom. It represented 2% of crude venom proteins, with pHi = 6 and molecular mass of 16889 Da. The reduction and the alkylation of LVP2 revealed an heterodimeric structure. Isolated alpha and beta chains of LVP2 have a molecular weight (MW) of 8822 Da and 8902, respectively. This protein was not toxic to mice and stimulated lipolysis on freshly dissociated rat adipocytes in a dose-dependent manner with EC50 = 2 +/- 0.75 microg/ml. LVP2 subunits did not display any lipolytic activity. As previously described for venom and LVP1, beta adrenergic receptor (beta AR) antagonists interfere with LVP2 activity. Furthermore, it is shown that LVP2 competes with [3H] CGP 12177 (beta1/beta2 AR antagonist) for binding to adipocyte plasma membrane with an IC50 of about 10(-7)M. Thus, these results bring original information on the existence of proteins that are present in scorpion venoms and can exert a distinct biological activity on adipocyte lipolysis through a beta-type adreno-receptor pathway.

Prevention of postischaemic ventricular fibrillation by long term beta adrenoceptor blockade with acebutolol in the anaesthetised dog.

Acute occlusions of the proximal left circumflex coronary arteriovenous pedicle were performed in open chest anaesthetised dogs. Twenty eight dogs were randomly allocated to receive acebutolol (3 mg X kg-1 twice daily) or placebo given blindly by mouth for five days; a control group of 14 dogs without any pretreatment underwent the same procedure. Coronary ligations in the randomised study were performed during seven consecutive days, and four dogs were operated on each day. This schedule was chosen in order to measure acebutolol plasma concentrations just before ligation from 60 to 540 min after the last dose of the drug. Long term oral treatment with acebutolol protected against postischaemic ventricular fibrillation and significantly reduced the incidence of both early phase (0-10 min postocclusion) ventricular arrhythmias and ventricular fibrillation. As a result the outcome was significantly improved after 60 min of ischaemia in acebutolol compared with placebo treated animals. The results in the control animals were similar to those in the placebo treated dogs. The protective effect of long term oral treatment with acebutolol lasted for nine hours and was apparently independent of the plasma concentrations of the drug. These data show that improved outcome in this canine model is due to the prevention of ischaemia induced ventricular fibrillation by long term beta adrenoceptor blockade, which is able to overcome the effect, if any, of partial agonist activity of acebutolol. A direct myocardial anti-ischaemic effect might explain the effectiveness of long term oral treatment, which is independent of plasma concentrations of the drug.

Triiodothyronine binding to liver nuclear solubilized proteins in vitro.

Nuclear proteins extracted from purified nuclei with 0.4M KCl at pH 7.4 OR 8.5 are able to bind L-triiodothyronine (T3) giving rise to nuclear thyroid hormone binding protein-T3 (NTBP-T3) complexes. Binding is maximum in 3 h at 20 C. It is thermolabile even at 36 C, inhibited by p-hydroxymercuribenzoate and markedly enhanced by dithiothreitol. Optimum pH is between 7.8 and 8.5. Divalent cations are not necessary. The NTBP-T3 complex exhibits similar anodal electrophoretic migration in polyacrylamide gel at pH 8.5, whether formed in vivo or in vitro. Scatchard plots obtained with various amounts of T3 from 0.15 nM TO 0.15 MUM and either unlabeled nuclear proteins or in vivo formed NTBP-[125I]-T3 complexes, give apparent association constants K-a of 0.2 X 10-10 M minus at pH 7.4 and 0.8 X 10-10 M minus 1 at pH 8.5. Capacity is about 0.5 pmol T3 per mg protein or 800 pg/g liver. The presence of dithiothreitol markedly enhances the Ka. The nuclear binding sites are not highly specific for L-T3 since they are able to bind D-T3 with almost equal affinity and triiodothyroacetic acid with a higher affinity. L-thyroxine (T4) can also displace L-T3 but with about 10-fold lesser effectiveness. Nuclear binding proteins of low capacity and high affinity have been demonstrated in vitro. The NTBP-T3 complexes formed in vivo, with whole nuclei, or in vitro are indistinguishable.

Triiodothyronine binding to isolated liver cell nuclei.

Nuclei of euthyroid rat liver have been prepared from homogenates by sedimentation through 2.3M sucrose with or without a 0.25% Triton wash. Triiodothyronine is accumulated by these nuclei during incubation in vitro in solutions containing 0.32M sucrose, 1mM MgCl2 and 0.02M Tris-Cl buffer at pH 7.4 or 7.85. Specific T3 binding sites occupied at 10-1,000 pM T3 are saturated by excess unlabeled T3 (0.15 muM). Specific T3 binding at 20 C is maximal at 203 hr nad is proportional to amount of nuclei. Calcium ion enhances nuclear integrity by reduces T3 accumulation. EDTA and phosphate ion cause nuclear damage but increase T3 accumulation. Binding is unaffected by inhibition of energy dependent reactions or of RNA synthesis. It is markedly increased under certain conditions by addition of dithiothreitol (DDT). Binding does not require mediation of a cytosol protein. T3 binding is not prevented by RNAse or DNAse, but is obliterated by pronase. Te binds to a nuclear iodothyronine binding protein (NTBP) to form an NTBP-T3 complex similar to that form-d after in vivo administration of the hormone. The complex can be extracted from the nuclei by 0.4M KC-. T3 present in the NTBP-T3 complex resists accumulation by anion exchange resin at 0-2C, but is bound by resin after 20 min at 37C or after addition of 0.1 mM p-hydroxymercuribenzoate. At pH 7.85 and with 5 mM DTT, the apparent Ka for isolated nuclei is 0.2 times 10-10M-1 and the capacity is 508 pg T3/g wet tissue or 53 times 10-15 moles T3/100 mug DNA. The data may not represent total capacity, but rather the amount of T3 dissociated during the period of incubation so that NTBP-T3 can be exchanged with labeled T3. Among analogues tested, triiodothyroacetic acid appears to bind with four times the affinity of L-TX, D-T3 binds with equal affinity, and L-T4 with one-fourth the affinity of T3.

Nuclear triiodothyronine receptor in differentiating preadipocytes cloned from obese and lean mice.

The nuclear T3 receptor was characterized in two T3-responsive preadipocyte cell lines cloned from the epididymal fat pads of ob/ob adult mice (ob 17 cells) and their lean counterpart (HGFu cells). Isolated nuclei from confluent or differentiating cells bound [125I]T3 to one class of high affinity sites exhibiting kinetic properties, stereospecificity, and salt extractibility of the nuclear T3 receptor. The solubilized T3 binding sites behave like the hepatic nuclear T3 receptor considering physicochemical and DNA binding properties. At confluence, no significant difference could be detected in equilibrium apparent affinity constant (Ka) and maximum binding capacity (MBC) for T3 whether nuclei were prepared from cells originating from ob/ob mice [Ka: 1.7 +/- (SE) 0.5 X 10(10) M-1; MBC: 432 +/- 29 fmol/mg DNA] or from lean mice (Ka: 1.6 +/- 0.2 X 10(10) M-1; MBC: 487 +/- 39 fmol/mg DNA). MBC values were in the range found in several T3-responsive tissues. This suggests that the primary defect in ob/ob mice is probably not at the level of the nuclear T3 receptor. Furthermore, during differentiation into adipose cells in both cell series, and roughly paralleling the amplifying effect of T3 on several lipogenic enzymes in the course of their development, the nuclear T3 receptor concentration significantly increased, attaining about twice the initial values after completion of the differentiation without any significant change in the affinity for T3.

Triiodothyronine (T3)-induced down-regulation of the nuclear T3 receptor in mouse preadipocyte cell lines.

As previously reported, preadipocytes cloned from the epididymal fat of lean or genetically obese mice (HGFu and ob 17, respectively) contain the nuclear T3 receptor. The number of receptor sites was similar in confluent cells of both lines and approximately doubled during adipocyte differentiation. T3 added to the culture medium increased triacylglycerol synthesis. T3 also increased fatty acid synthase specific activity, relative synthesis rate, and relative mRNA content (1.5- to 2.5-fold). Optimal responses were obtained at 1.5 nM. This study shows that under the same culture conditions in both cell lines, 1.5 nM T3 decreased the receptor concentration with no significant change in the affinity for T3. The receptor depletion was time dependent, rapid, stable in the presence of T3, and reversible in less than 24 h after its withdrawal. Receptor depletion was also dependent on T3 concentration and close to maximum at 1.5 nM T3 [45.1 +/- 2.7% (+/- SE) of the data values without T3; n = 14]. A linear relationship was observed between receptor occupancy by T3 and receptor loss. T4 and triiodothyroacetic acid also decreased the T3 receptor content, as expected from their own affinity for the receptor. These last two observations suggest that the receptor reduction is related to its occupancy by T3. The reported results, also observed in several other cell types, indicate that down-regulation of the nuclear T3 receptor by thyroid hormones is probably a generalized event in T3 target cells at least in vitro. Interpretation of its significance in preadipocyte cell lines requires further studies of rapid nuclear events following T3 receptor occupancy.

Retinoic acid decreases nuclear triiodothyronine receptor expression and impairs an early step of adipose differentiation in the thyroid hormone-sensitive mouse Ob 17 preadipocyte cell line.

In the murine preadipocyte cell line Ob 17, T3 is known to be necessary at an early step of adipose differentiation for the expression of late phenotypes [lipogenic enzymes such as malic enzyme, glycerol-3-phosphate dehydrogenase (GPDH), etc.] and not necessary for the expression of lipoprotein lipase (LPL), which emerges earlier, at growth arrest. These cells contain nuclear T3 receptors, which mainly belong to products of the c-erbA alpha gene and are down-regulated by T3. In this work, retinoic acid (RA) added to Ob 17 cells at growth arrest impaired morphological differentiation and the development of both late (malic enzyme and GPDH) and early (LPL) phenotypes regardless of whether T3 was added. T3 sensitized the cells to the inhibitory action of RA; the ED50 for GPDH activity was shifted from 0.5 microM to 3 nM in cells cultured with 1.5 nM T3. Later addition of RA (6 days after growth arrest) did not inhibit the differentiation. RA also brought out a marked and fast decrease in nuclear T3 receptors. This was observed whatever the stage of cell development and related to both a rapid decrease in the relative abundance of c-erbA alpha-related mRNA species and an increased disappearance rate, suggesting the involvement of pre- and posttranslational events. RA and T3 acted additively in decreasing the T3 receptor and c-erbA alpha mRNA levels. The effects of RA on T3 receptors were rapidly reversed after RA withdrawal; the reversal was large (75%) when RA was introduced at growth arrest and total when introduced later. The cell sensitivity to RA, considering the T3 receptors, was higher at growth arrest (ED50 for RA, 0.2 and 1.5 microM in assays with RA added at growth arrest and 5 days later, respectively). The results suggest intricated regulatory pathways between RA and T3 at an early step of adipose differentiation and also suggest that among different mechanisms through which RA may impair this differentiation, a decreased level of nuclear T3 receptors at an early period should play a role.

Calcitriol down-modulates the 3,5,3' triiodothyronine (T3) receptors and affects, in a biphasic manner, the T3-dependent adipose differentiation of Ob 17 preadipocytes.

In previous reports, we showed that T3 is required for terminal differentiation of the murine Ob 17 preadipocytes, and that it partially down-modulates the abundance of its own nuclear receptor sites (T3R). We also reported that a profound depletion of the T3R was produced by all-trans-retinoic acid at concentrations that inhibit adipose differentiation. Here, we report that calcitriol (VD), which activates a nuclear receptor (VDR) closely related to the T3R and retinoid receptors, also markedly affects nuclear T3 binding and T3-induced differentiation of Ob 17 cells. Within a nearly physiological concentration range (0.1-2.5 nM), calcitriol profoundly down-modulated T3R abundance without altering the affinity for T3. The T3R depletion was a fast event, sustained under VD and reversed within 48 h of VD withdrawal. The order of efficient concentration ranges of VD and analogs suggests an involvement of the VDR. The T3R-depleting effect of VD was observed at every stage of adipose differentiation and was additive to the depleting effect of T3. Within the 0.1-2.5 nM VD concentration range, the c-erbA alpha and -alpha 1 messenger RNA levels (only c-erbA alpha gene products were detected in these cells) were poorly decreased; VD also did not alter a protein band specifically detected with specific anti-c-erbA alpha 1 antibodies in Western blots of nuclear extracts. VD accelerated the T3R disappearance rate; the results suggest that this would probably involve sequestration, rather than degradation, events. Interestingly, calcitriol added to the culture medium of Ob 17 preadipocytes markedly influenced the adipose differentiation, exerting a clear-cut stimulation at levels of 0.25 nM or less and profound inhibition at concentrations above 0.25 nM. Both effects were observed provided that VD was added within an early critical period of the differentiation process, as we previously reported for T3. The stimulations caused by low concentrations of VD and 1.5 nM T3 were additive. Increasing the VD concentration produced a progressive attenuation, then a suppression, of the stimulating effect of T3. Comparative analyses of VD-related changes in adipose differentiation and T3R abundance suggest that a correlation may exist between optimal differentiation and a partial depletion of the T3R, whereas a profound depletion of the T3R occurred at inhibitory concentrations of VD. The present results sustain the concept that T3R play a role in the differentiation of Ob 17 preadipocytes. Moreover, the results suggest that there may be a T3 receptor site concentration optimal for efficient differentiation. A regulation of this concentration involves ligands of other closely related receptors and, thus, probably the interplays that exist between these receptors.

Transient expression of c-erbAbeta1 messenger ribonucleic acid and beta1 thyroid hormone receptor early in adipogenesis of Ob 17 cells.

In the murine Ob 17 preadipocyte cell line, the thyroid hormone T3 is an adipogenic factor necessary at an early stage for differentiation into adipocyte. We demonstrate here that this T3 dependence may involve a transient expression (at both the messenger RNA and the protein levels) of c-ErbA beta-type receptors (T3R), although a large body of T3R remained the product of the c-erbAalpha gene, as previously described. c-ErbAbeta1 (and not beta2) expression emerged significantly at growth arrest, peaked 2 days later, and almost disappeared in maturing adipocytes. This expression is related to the presence of T3, as total deprivation of culture medium from T3 prevented it, and the addition of 1.5 nM T3 to preconfluent cultures was able to restore it. When cells were cultured in the presence of T3 and thus were able to differentiate, the c-erbAbeta peak was accompanied by sequential rapid increases in CAAT/enhancer-binding protein-delta(C/EBPdelta), peroxisome proliferator-activated-gamma receptor (PPARgamma), and C/EBPalpha gene expressions. On the contrary, under thyroid hormone-deprived culture conditions that result in nondifferentiation of the preadipocytes, c-erbAbeta1, PPARgamma, and the large C/EBPalpha expressions were blunted, and a moderate early increase in c-erbAalpha1 transcripts was sustained for a longer period. Addition of T3 to T3-deprived preconfluent cells restored PPARgamma and C/EBPalpha expressions. Taken together, the results highlight the important role of T3 in the adipogenesis of Ob 17 cells through the involvement of both beta1 and alpha1 T3R subtypes.

Production of rat Spot14 protein in Escherichia coli.

Hormonal, nutritional and developmental factors modulate, in rat lipogenic tissues, the transcription of the mRNA coding for a protein of unknown function, called Spot14 (S14). The corresponding protein has never been purified from tissues. In this paper, we describe the production of S14 in Escherichia coli. In the absence of available antibodies (Ab) directed against S14 protein, our strategy was to produce this protein by constructing two different recombinant expression vectors. The first recombinant plasmid produced a S14::protein A fusion which was easily purified and then rabbit Ab could be raised against it. The second expression vector directly produced S14. This expression was demonstrated by specific binding of polyclonal Ab directed against the fusion protein. These Ab also recognized a rat-liver protein sharing characteristics of S14.

Nuclear factors specifically favor thyroid hormone binding to c-ErbA alpha 1 protein (thyroid hormone receptor alpha) over-expressed in E. coli.

A recombinant rat thyroid hormone receptor alpha (TR alpha or c-ErbA alpha 1) was produced in E. coli as a non-mutated, nonfusioned protein and obtained as an efficient DNA and T3 binding protein that could be easily handled in a buffer-soluble state (rec-TR alpha). It was found that nuclear extracts (NE) added to rec-TR alpha markedly amplified not only DNA binding, which has been well documented, but also T3 binding (increased binding site concentration), which has not yet been reported. This T3 binding amplifying effect on rec-TR alpha occurs at low NE protein concentrations that produce no or minimal endogenous TR with respect to rec-TR, while similar concentrations of other proteins (e.g. ovalbumin or cytosol) only moderately enhanced T3 binding. The T3 binding amplifying nuclear factors, which are partly heat-labile, appeared as necessary auxiliaries in the analyses of partially purified rec-TR alpha. A protective effect of NE against a loss of affinity for T3 under the action of antibodies directed to certain sequences in the TR alpha D domain suggests that nuclear factors help rec-TR alpha to acquire and/or stabilize a conformation that allows the high affinity T3 binding. The nature of this nuclear amplifying factor is still unknown: RXR alpha which, produced in vitro, could amplify binding of the rec-TR alpha to a DNA thyroid response element, was unable to display such a rescue of high affinity binding sites.

Heterogeneous distribution of nuclear triiodothyronine receptors in liver and preadipose cells as evidenced by their reactivity to antibodies against different protein products of erb A oncogenes.

Polyclonal antibodies raised in rabbits against bacterially produced peptides in the C-terminal region of v-erb A or human c-erb A alpha oncogenes recognize the nuclear triiodothyronine (T3) receptors in the T3-sensitive Ob 17 mouse preadipocyte cell line and not in mouse or rat liver. The results confirm the existence of different T3 receptors in different tissues. The results also suggest a heterogeneous receptor distribution within the preadipose cell line, with a predominance of c-erb A alpha-type species. Antibodies raised against domain 149 227, but not against domain 245-325, impair T3 binding, suggesting a role for this domain in ligand binding.

Cloning and initial characterization of human and mouse Spot 14 genes.

The intricate regulation of Spot 14 expression in rat lipogenic tissues has provided a useful tool in studying nutritional and hormonal factors involved in transcription. To gain insight into its function and its possible involvement in human lipid disorders, we cloned human and mouse Spot 14 genes that shared with the rat gene a strong homology concerning the deduced amino acid sequence (81 and 94%, respectively) as well as the promoter region. The mouse promoter was characterized by transfection studies, while quantitative RT-PCR and in situ hybridization experiments showed that Spot 14 is expressed in human liver and, at a high level, in multiple symmetric lipomatosis nodules.

Bretylium tosylate in patients with acute myocardial infarction.

Experience with bretylium tosylate accumulated during a period of over 10 years, during which time greater than 1,500 patients with acute myocardial infarction were treated, is summarized. On the diagnosis of acute infarction, the agent was given by continuous intravenous drip at a rate of 10 mg/kg/24 hours for 5 to 7 days for prophylaxis of ventricular fibrillation. Bretylium administration prevented primary ventricular fibrillation in about 99% of these patients. No undesirable side effects were observed with this protocol, which lessens the initial sympathomimetic effect of the drug while allowing sufficient time for the adrenergic neuronal blocking effect to develop. The beneficial effects of the drug are believed to be due, in part, to a direct electrophysiologic effect on both normal and ischemic myocardium. This effect equalizes the duration of both the effective refractory periods and the ventricular action potentials, and it creates conditions capable of blocking reentrant pathways. Bretylium stabilizes the duration of electrical systole in patients with acute myocardial infarction. Hemodynamic studies during bretylium treatment further confirm the effectiveness of this drug and have prompted additional studies to evaluate its potential as an agent capable of decreasing impedance in acute myocardial infarction.