Molecular cloning of cDNA for rat L-type pyruvate kinase and aldolase B

Two double-stranded cDNA recombinant pBR322 plasmid libraries were constructed starting from high carbohydrate diet rat liver poly(A)+ mRNA, either fractionated by denaturing sucrose gradient centrifugation for the cloning of L-type pyruvate kinase cDNA, or nonfractionated for aldolase B. Both libraries were screened with single-stranded cDNA probes reverse transcribed from fasted or high carbohydrate diet rat liver mRNAs. mRNAs from fasted animals were also fractionated by sucrose gradient centrifugation and mRNAs from the fed animals were, in addition, further purified by high performance liquid gel filtration chromatography. Those clones hybridizing with the "positive" probe (from animals fed the high carbohydrate diet) and not with the "negative" one (from fasted animals) were preselected and their plasmid DNA was purified and analyzed by positive hybridization-selection. Thirty of 4500 bacteria colonies transformed by recombinant plasmids were preselected by differential screening for pyruvate kinase, and 8 of 864 colonies for aldolase B. Twenty-two recombinant plasmids for pyruvate kinase and two for aldolase B were shown to contain specific cDNA inserts by positive hybridization-selection. Plasmids DNAs of some pyruvate kinase and aldolase B clones (whose inserts ranged from 700 to 1050 bases in length) were labeled by nick translation and used as probes for Northern blot hybridization. The pyruvate kinase cDNA probes recognized mainly a 3400-base RNA species which was detected in high carbohydrate diet rat liver, but not in fasted rat liver and in tissues which do not synthesize L-type pyruvate kinase. In addition, some pyruvate kinase probes hybridized with minor RNA species of about 2000 bases in length, only observed after carbohydrate diet. For aldolase B, the recombinant plasmid DNA hybridized with a single RNA species of 1750 bases. This RNA, detected in kidney, small intestine and liver, was induced by a high carbohydrate diet and increased with liver development. The rat probe cross-hybridized with human aldolase B messenger RNA.     

Cloning and expression of mouse fatty acid synthase and other specific mRNAs. Developmental and hormonal regulation in 3T3-L1 cells

Mouse liver mRNA enriched in sequence coding for fatty acid synthase by sucrose density gradient centrifugation was used as template for cDNA synthesis. Double-stranded cDNA sequences were inserted into pBR322 and lambda gt10 and cloned. Clones containing putative cDNA sequences for fatty acid synthase were identified by differential hybridization with [32P] cDNAs synthesized from sucrose gradient-purified liver mRNA from mice fasted or fasted and refed a high carbohydrate diet. Thirteen out of 45 differentially expressed clones were found to contain sequences complementary to fatty acid synthase mRNA. Northern blot analysis revealed that, unlike in avian and rat tissues, a single 8.2-kilobase (kb) mRNA codes for fatty acid synthase in mice. In addition to the fatty acid synthase cDNA clones, cDNA clones to two specific mRNAs of 5.1 and 7.2 kb were selected to study nutritional, hormonal, and developmental regulation at the level of mRNA abundance in mouse liver and in 3T3-L1 cells. The induction of fatty acid synthase in the livers of previously fasted mice fed a high carbohydrate diet was controlled pretranslationally by modulation of the fatty acid synthase mRNA content. The level of the two mRNAs with sizes of 5.1 and 7.2 kb were also elevated dramatically in the liver of mice fasted and refed a high carbohydrate diet. A detectable, but very low level of fatty acid synthase mRNA was found in 3T3-L1 preadipocytes. During the differentiation to adipocytes, both the rate of synthesis and relative mRNA level for fatty acid synthase increased in a parallel fashion to a maximum of 17-fold. The levels of 5.1- and 7.2-kb mRNAs, coding for proteins possibly involved in lipogenesis, increased 45- and 25-fold, respectively, during differentiation of 3T3-L1 adipocytes. Treatment of mature 3T3-L1 adipocytes with insulin elicited a 3-fold increase in both rate of synthesis and mRNA content of fatty acid synthase, while treatment with dibutyryl cAMP caused a 60% decrease in fatty acid synthase mRNA and an 80% decrease in the rate of the enzyme synthesis, indicating pretranslational control of fatty acid synthase expression by the lipogenic and lipolytic hormones. Similarly, insulin caused a 2- to 3-fold increase in both 7.2- and 5.1-kb mRNAs and dibutyryl cAMP decreased the levels of 7.2- and 5.1-kb mRNAs to 10 and 20% of control levels, respectively.     

Effects of thyroid state on the expression of hepatic thyroid hormone transporters in rats

Liver uptake of thyroxine (T4) is mediated by transporters and is rate limiting for hepatic 3,3',5-triiodothyronine (T3) production. We investigated whether hepatic mRNA for T4 transporters is regulated by thyroid state using Xenopus laevis oocytes as an expression system. Because X. laevis oocytes show high endogenous uptake of T4, T4 sulfamate (T4NS) was used as an alternative ligand for the hepatic T4 transporters. Oocytes were injected with 23 ng liver mRNA from euthyroid, hypothyroid, or hyperthyroid rats, and after 3-4 days uptake was determined by incubation of injected and uninjected oocytes for 1 h at 25 degrees C or for 4 h at 18 degrees C with 10 nM [125I]T4NS. Expression of type I deiodinase (D1), which is regulated by thyroid state, was studied in the oocytes as an internal control. Uptake of T4NS showed similar approximately fourfold increases after injection of liver mRNA from euthyroid, hypothyroid, or hyperthyroid rats. A similar lack of effect of thyroid state was observed using reverse T3 as ligand. In contrast, D1 activity induced by liver mRNA from hyperthyroid and hypothyroid rats in the oocytes was 2.4-fold higher and 2.7-fold lower, respectively, compared with euthyroid rats. Studies have shown that uptake of iodothyronines in rat liver is mediated in part by several organic anion transporters, such as the Na+/taurocholate-cotransporting polypeptide (rNTCP) and the Na-independent organic anion-transporting polypeptide (rOATP1). Therefore, the effects of thyroid state on rNTCP, rOATP1, and D1 mRNA levels in rat liver were also determined. Northern analysis showed no differences in rNTCP or rOATP1 mRNA levels between hyperthyroid and hypothyroid rats, whereas D1 mRNA levels varied widely as expected. These results suggest little effect of thyroid state on the levels of mRNA coding for T4 transporters in rat liver, including rNTCP and rOATP1. However, they do not exclude regulation of hepatic T4 transporters by thyroid hormone at the translational and posttranslational level.     

Thyroid hormone stimulation of NADPH P450 reductase expression in liver and extrahepatic tissues. Regulation by multiple mechanisms.

The role of thyroid hormone in regulating the expression of the flavoprotein NADPH cytochrome P450 reductase was studied in adult rats. Depletion of circulating thyroid hormone by hypophysectomy, or more selectively, by treatment with the anti-thyroid drug methimazole led to a 75-85% depletion of hepatic microsomal P450 reductase activity and protein in both male and female rats. Thyroxine substantially restored P450 reductase activity at a dose that rendered the thyroid-depleted rats euthyroid. Microsomal P450 reductase activity in several extrahepatic tissues was also dependent on thyroid hormone, but to a lesser extent than in liver (30-50% decrease in kidney, adrenal, lung, and heart but not in testis from hypothyroid rats). Hepatic P450 reductase mRNA levels were also decreased in the hypothyroid state, indicating that the loss of P450 reductase activity is not a consequence of the associated decreased availability of the FMN and FAD cofactors of P450 reductase. Parallel analysis of S14 mRNA, which has been studied extensively as a model thyroid-regulated liver gene product, indicated that P450 reductase and S14 mRNA respond similarly to these changes in thyroid state. In contrast, while the expression of S14 and several other thyroid hormone-dependent hepatic mRNAs is stimulated by feeding a high carbohydrate, fat-free diet, hepatic P450 reductase expression was not increased by this lipogenic diet. Injection of hypothyroid rats with T3 at a supraphysiologic, receptor-saturating dose stimulated a major induction of hepatic P450 reductase mRNA that was detectable 4 h after the T3 injection, and peaked at approximately 650% of euthyroid levels by 12 h. However, this same treatment stimulated a biphasic increase in P450 reductase protein and activity that required 3 days to reach normal euthyroid levels. T3 treatment of euthyroid rats also stimulated a major induction of P450 reductase mRNA that was maximal (12-fold increase) by 12 h, but in this case no major increase in P450 reductase protein or activity was detectable over a 3-day period. Together, these studies establish that thyroid hormone regulates P450 reductase expression by pretranslational mechanisms. They also suggest that other regulatory mechanisms, which may involve changes in P450 reductase protein stability and/or changes in the translational efficiency of its mRNA, are likely to occur.     

Upregulation of Slc39a10 gene expression in response to thyroid hormones in intestine and kidney

A novel zinc transporter has been purified and cloned from rat renal brush border membrane. This transporter was designated as Zip10 encoded by Slc39a10 gene and characterized as zinc importer. Present study documents the impact of thyroid hormones on the expression of Zip10 encoded by Slc39a10 gene in rat model of hypo and hyperthyroidism. Serum T(3) and T(4) levels were reduced significantly in hypothyroid rats whereas these levels were significantly elevated in hyperthyroid rats as compared to euthyroid rats thereby confirming the validity of the model. Kinetic studies revealed a significant increase in the initial and equilibrium uptake of Zn(++) in both intestinal and renal BBMV of hyperthyroid rats in comparison to hypothyroid and euthyroid rats. By RT-PCR, Slc39a10 mRNA expression was found to be significantly decreased in hypothyroid and increased in hyperthyroid as compared to euthyroid rats. These findings are in conformity with the immunofluorescence studies that revealed markedly higher fluorescence intensity at periphery of both intestinal and renal cells isolated from hyperthyroid rats as compared to hypothyroid and euthyroid rats. Higher expression of Zip10 protein in hyperthyroid group was also confirmed by western blot. These findings suggest that expression of zinc transporter protein Zip10 (Slc39a10) in intestine and kidney is positively regulated by thyroid hormones.     

Expression of myosin heavy chains during thyroid hormone-induced cardiac growth

The expression of mRNAs for two cardiac myosins has been studied in the ventricles of hypo- and hyperthyroid rabbits by using cloned cDNA sequences corresponding to the mRNAs of the alpha- and beta-myosin heavy chains (HCs). The temporal change in relative levels of the alpha and beta HC mRNAs after triiodothyronine (T3) treatment of hypothyroid rabbits was determined by nuclease S1 mapping. In the hypothyroid state, only NC beta-mRNA was expressed in the ventricles. The HC alpha-mRNA was first detectable 4 h after administration of T3 (200 micrograms/kg) to hypothyroid animals. By 12, 24, and 72 h, HC alpha-mRNA represented 20, 50, and 90% of total myosin mRNA. The relationship between the relative mRNA levels and relative synthesis rates of myosin HCs was evaluated in 5- to 6-wk-old normal and thyrotoxic rabbits. Myosin synthesis rates were determined by labeling of protein in vivo with [2H]leucine. The V1 (HC alpha) and V3 (HC beta) isomyosins were separated by immune affinity chromatography and the HCs were isolated electrophoretically. In a normal euthyroid group of animals and in animals 12 and 24 h after administration of 200 micrograms of thyroxine, the relative mRNA levels and relative synthesis rates of the alpha and beta HCs were not significantly different. Our results show that, first, thyroid hormone causes a rapid accumulation of HC alpha-mRNA and loss of HC alpha-mRNA, and second, in normal and thyrotoxic rabbits, the relative synthesis rates of HC alpha and HC beta reflect the relative abundance of their respective mRNAs. These data are consistent with the thyroid hormones regulating synthesis of ventricular myosin at steps that precede translation of its message.     

Changes in the rates of synthesis and messenger RNA levels of hepatic glucose-6-phosphate and 6-phosphogluconate dehydrogenases following induction by diet or thyroid hormone

The lipogenic capacity of rat liver is increased in animals fed a high carbohydrate, fat-free diet or by the administration of 2,2',5'-triiodo-L-thyronine. Underlying this change is a generalized induction of the enzymes involved in lipogenesis, including glucose-6-phosphate dehydrogenase, 6-phosphogluconate dehydrogenase, and malic enzyme, which together serve to generate the additional NADPH required for increased fatty acid synthesis. This report presents evidence indicating that induction of the hexose-shunt dehydrogenases involves increased enzyme synthesis secondary to elevated enzyme specific mRNA levels, as has previously been shown for malic enzyme. Activities of specific mRNAs, estimated by cell-free translation of hepatic poly(A)-containing RNA in the mRNA dependent rabbit reticulocyte lysate, were compared with enzyme specific activities and relative rates of specific enzyme synthesis. The 2-fold increase in glucose-6-phosphate dehydrogenase specific activity in hyperthyroid rats and the 13-fold increase in rats fed a high carbohydrate, fat-free diet, relative to euthyroid, chow-fed controls were paralleled by comparable increases in the synthetic rates and mRNA levels of this enzyme. Similarly, consonant changes in the rate of enzyme synthesis and concentration of 6-phosphogluconate dehydrogenase mRNA accompanied the 2.5- and 3-fold increases in specific activity of this enzyme observed in response to hormonal and dietary induction, respectively. Thus, both thyroid hormone and carbohydrate feeding appear to induce glucose-6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase primarily by increasing the effective cellular concentrations of their respective mRNAs and, consequently, their rates of synthesis.     

The use of intramuscularly administered methyl-TRH to evaluate the pituitary-thyroid axis.

The present study was carried out to evaluate the effectiveness of intramuscular administration of methyl-TRH, a potent analogue of thyrotropin-releasing hormone, for assessing pituitary reserve of TSH and prolactin and for distinguishing euthyroid, hypothyroid and hyperthyroid individuals. Serum samples were taken for 24 hours after intramuscular injection of methyl-TRH, 200 microgram, in 19 euthyroid subjects, 9 hypothyroid men and 9 hyperthyroid men. The mean serum prolactin and TSH concentrations were significantly elevated over baseline levels at 30 min in the euthyroid individuals and remained elevated for 3 to 4 hours. The serum TSH, T3 and T4 responses after intramuscular methyl-TRH in euthyroid subjects were clearly distinguishable from those of hyperthyroid and hypothyroid patients. Significant elevation of the serum T3 and T4 concentrations at 24 hours after intramuscular injection of methyl-TRH shows the sustained effect of this TRH analogue in euthyroid subjects.     

Rapid synergistic interaction between thyroid hormone and carbohydrate on mRNAS14 induction

Recent studies have shown that hepatic mRNAS14 responds rapidly to thyroid hormone administration. Moreover, this mRNA is known to increase in mass with the administration of a high carbohydrate fat-free diet. Therefore, it appears to share many of the same properties of the known hepatic lipogenic enzymes. Because the lipogenic enzymes display a synergistic interaction between thyroid hormones and carbohydrates, we investigated the kinetics of response of mRNAS14 to carbohydrate feeding, as well as its interaction with triiodothyronine (T3). We found that mRNAS14 responds rapidly to the dietary administration of sucrose in euthyroid rats, with a 2-fold increase within 30 min, and a 25-fold increase by 4 h. On the other hand, when given to hypothyroid rats, sucrose ultimately lead to only a 2-3-fold increase in the level of mRNAS14, attaining a level less than that found in starved euthyroid rats. The diminished response of mRNAS14 to sucrose in hypothyroidism could not be enhanced by insulin administration. However, administration of replacement doses of T3 (400 ng/100 g of body weight) immediately restored the rapid response to sucrose feeding. The response of sucrose and T3 was synergistic. Dose-response studies with T3 indicated that the rapid interaction between T3 and sucrose was limited by the occupancy of the T3 nuclear receptor. A similar synergistic response to T3 and glucose was noted in primary hepatocyte cultures, thus indicating that the synergism between these two stimuli is not due to changes in extrahepatic hormones or metabolites. Our data are most consistent with the hypothesis that the T3-nuclear receptor complex multiplies a signal generated by carbohydrate metabolism to induce hepatic mRNAS14. The interaction does not appear to require the preliminary induction of carbohydrate-metabolizing enzymes and their mRNAs.     

Molecular cloning of cDNA for rat acyl-CoA oxidase

Poly(A+) RNA was prepared from hepatic free polysomes of rats which had been fed di(2-ethylhexyl) phthalate for the induction of peroxisomal beta-oxidation enzymes. This preparation was enriched for the mRNAs of these enzymes by sucrose density gradient centrifugation, and used for the synthesis of double-stranded cDNA. Recombinant plasmids were constructed from the cDNA and pBR322 by dG X dC-tailing method and used for the transformation of an Escherichia coli strain, chi 1776. By differential colony hybridization using [32P]cDNA of partially purified liver poly(A+) RNA from induced and noninduced rats as probes, and then by hybridization-selected translation, we obtained two clones with cDNA inserts which specifically selected acyl-CoA oxidase mRNA. On Northern blotting, both cDNA inserts hybridized to 3.8-kilobase RNA which was increased about 10-fold by di(2-ethylhexyl) phthalate treatment of the rats. The cleavage maps of the cDNA inserts showed they overlap with each other. We conclude that the above two recombinant plasmid clones contain cDNA sequences for rat acyl-CoA oxidase.     

Thyroid hormone may induce changes in the concentration of the mitochondrial calcium uniporter

We explored the possibility that the hormone 3,3',5-tri-iodothyronine can regulate the biosynthesis of the mitochondrial calcium uniporter. To meet this objective experiments on Ca(2+) transport, and binding of the specific inhibitor Ru(360) were carried out in mitochondria isolated from euthyroid, hyperthyroid and hypothyroid rats. It was found that V(max) for Ca(2+) transport increased from 11.67+/-0.8 in euthyroid to 14.36+/-0.44 in hyperthyroid, and decreased in hypothyroid mitochondria to 8.62+/-0.63 nmol Ca(2+)/mg/s. Furthermore, the K(i) for the specific inhibitor Ru(360), depends on the thyroid status, i.e. 18, 19 and 13 nM for control, hyper- and hypothyroid mitochondria, respectively. In addition, the binding of 103Ru(360) was increased in hyperthyroid and decreased in hypothyroid mitochondria. Scatchard analysis for the binding of 103Ru(360) showed the following values: 28, 40 and 23 pmol/mg for control, hyper- and hypothyroid mitochondria, respectively. The K(d) for 103Ru(360) was found to be 30.39, 37.03 and 35.71 nM for controls, hyper- and hypothyroid groups, respectively. When hypothyroid rats were treated with thyroid hormone, mitochondrial Ca(2+) transport, as well as 103Ru(360) binding, reached similar values to those found for euthyroid mitochondria.     

Flow cytometry phenotypization of thyroidal lymphoid infiltrate and functional status in Hashimoto's thyroiditis

OBJECTIVE: To evaluate the thyroidal lymphoid infiltrate (TLI) in thyroidal functional status (TFS) for differences among patients with Hashimoto's thyroiditis (HT). STUDY DESIGN: Flow-cytometry (FC) was applied to thyroidal fine-needle cytology samples in 57 patients. TLI was analyzed using a fluorescence-activated cell sorter (FACS) scan and fluorescence antibodies CD3, CD4, CD5, CD8, CD10, and CD19 and kappa and lambda light chains. TFS was determined by serum thyroid-stimulating hormone (TSH), FT3 and FT4 immunoassays, in specific clinical settings, to classify the cases as hyperthyroid, euthyroid and hypothyroid. FC assessment was then compared with the corresponding TFS. RESULTS: B-lymphocytes were present in 44 cases (77%). T-lymphocytes were present in all the cases; CD4/CD8 = 2:1 ratio was observed in 16 euthyroid, 1 hyperthyroid and 3 hypothyroid; CD4/CD8 > or = 3:1 ratio in 22 euthyroid, 2 hyperthyroid and 2 hypothyroid cases; CD4/CD8 < or = 1:1 ratio in 1 euthyroid, 3 hyperthyroid and in 7 hypothyroid cases. Grouping hyperthyroid and hypothyroid cases, a significant association was observed with the CD4/CD8 < or = 1:1 ratio (p < 0.01). CONCLUSION: Intrathyroidal CD4/CD8 < 1:1 ratio might be the expression of intense apoptosis in the early phases of HT, generally followed by the restoration of CD4/CD8 balance; persistence of increased intrathyroidal CD8 might be related to intense thyroidal damage and thus an increasing risk of hypothyroidism.     

Thyroid hormone differentially affects mRNA levels of Ca-ATPase isozymes of sarcoplasmic reticulum in fast and slow skeletal muscle

mRNA levels for the type I and type II isoforms of sarcoplasmic reticulum (SR) Ca-ATPase were determined in soleus (SOL) and extensor digitorum longus (EDL) muscle of euthyroid (normal), hypothyroid, and hyperthyroid rats. Total Ca-ATPase mRNA content of hyperthyroid muscle was 1.5-fold (EDL) and 6-fold (SOL) higher compared to hypothyroid muscle, with corresponding increases in total SR Ca-ATPase activity. EDL contained only type II Ca-ATPase mRNA. In SOL type I mRNA was the major form in hypothyroidism (98%), but the type II mRNA content was stimulated 150-fold by T3, accounting for 50% of the Ca-ATPase mRNA in hyperthyroidism.     

Synthesis and cloning of DNA complementary to mRNA of the bovine mammary gland

Poly(A+)mRNA from bovine mammary glands was used to synthesize double-stranded cDNAs that were subsequently inserted into the plasmid vector pBR322 at the Pst1 site by means of oligo(dG)-oligo(dC) tailing. After transfection of Escherichia coli JC5183, recombinant plasmid library containing 5400 clones was screened by serial rounds of colony hybridization in situ to total [23P] poly(A+)mRNA and electrophoretically homogenious [32P]16SmRNA of mammary glands. Then hybrid selection of mRNA and subsequent in vitro translation of selected mRNAs were performed. In this manner, recombinant clones coding for alpha S1- beta-, kappa-casein were identified. cDNA clones range in size from 35% for beta-casein, 65% for alpha S1-casein to about 95% for kappa-casein, in comparison with their respective mRNAs.     

Effect of thyroid state on susceptibility to oxidants and swelling of mitochondria from rat tissues

The effects of the thyroid state on oxidative damage, antioxidant capacity, susceptibility to in vitro oxidative stress and Ca(2+)-induced permeabilization of mitochondria from rat tissues (liver, heart, and gastrocnemious muscle) were examined. Hypothyroidism was induced by administering methimazole in drinking water for 15 d. Hyperthyroidism was elicited by a 10 d treatment of hypothyroid rats with triiodothyronine (10 micro g/100 g body weight). Mitochondrial levels of hydroperoxides and protein-bound carbonyls significantly decreased in hypothyroid tissues and were reported above euthroid values in hypothyroid rats after T(3) treatment. Mitochondrial vitamin E levels were not affected by changes of animal thyroid state. Mitochondrial Coenzyme Q9 levels decreased in liver and heart from hypothyroid rats and increased in all hyperthyroid tissues, while Coenzyme Q10 levels decreased in hypothyroid liver and increased in all hyperthyroid tissues. The antioxidant capacity of mitochondria was not significantly different in hypothyroid and euthyroid tissues, whereas it decreased in the hyperthyroid ones. Susceptibility to in vitro oxidative challenge decreased in mitochondria from hypothyroid tissues and increased in mitochondria from hyperthyroid tissues, while susceptibility to Ca(2+)-induced swelling decreased only in hypothyroid liver mitochondria and increased in mitochondria from all hyperthyroid tissues. The tissue-dependence of the mitochondrial susceptibility to stressful conditions in altered thyroid states can be explained by different thyroid hormone-induced changes in mitochondrial ROS production and relative amounts of mitochondrial hemoproteins and antioxidants. We suggest that susceptibilities to oxidants and Ca(2+)-induced swelling may have important implications for the thyroid hormone regulation of the turnover of proteins and whole mitochondria, respectively.