Degree of catecholamine hypersecretion is the most important determinant of intra-operative hemodynamic outcomes in pheochromocytoma

Pheochromocytoma resection is often complicated by intra-operative hypertension and post-resection hypotension. Factors associated with these hemodynamic alterations are not well defined. The aim of this study was to analyse the clinical-laboratory features associated with hemodynamic parameters during pheochromocytoma resection. Twenty-seven patients submitted to tumor resection - either open (no.=18) or video laparoscopic - between 1978-2007 were included. Nineteen received pre-operative alpha-blockers. Intra-operative hemodynamic data analysed were: maximum and minimum mean arterial blood pressure (MABP), no. of severe hypertensive (systolic BP >200 mmHg) and hypotensive episodes (MABP <60 mmHg), maximum and minimum heart rate (HR), no. of episodes of tachycardia and bradycardia, need to receive iv intra-operative treatment for hypertension and hypotension and the volume of fluids administered during surgery. Patients were 39.4+/-14.4-yr-old, 66% women. Intra-operative hemodynamic parameters were not different in patients submitted to open or video laparoscopic resection. Maximum intraoperative HR and the percentage of patients with HR>100 beats/min were higher in patients without pre-operative alpha- blocker treatment (no.=8). Pre-operative urinary vanylmandelic acid was positively associated with intra-operative maximum MABP (r=0.535, p=0.047) and with maximum transoperative systolic BP (r=0.805, p=0.016). Pre-operative urinary catecholamine (Pearson correlation r=0.575, p=0.03) and vanylmandelic acid (Pearson correlation r=0.605, p=0.04) levels were associated with maximum intra- operative MABP, adjusted for the presence of pheochromocytoma symptoms, surgical approach and pre-operative alpha-blockers. In conclusion, the degree of pre-operative catecholamine secretion was the most important aspect of transoperative BP control.

H-RAS gene expression in human multinodular goiter

The RAS protooncogene has an important, although not yet established role in thyroid neoplasia. In this study, we evaluated the H-RAS mRNA and protein levels in human samples of nontoxic and toxic multinodular goiter samples, according to serum TSH levels. The mean of H-RAS mRNA levels in nodules of nontoxic nodular goiter were significantly increased compared to nonnodular tissue (1.49+/-1.21 vs. 0.94+/-0.81 AU, P=0.016). Nine of the 18 specimens (50%) of nontoxic multinodular goiter exhibited increased levels of H-RAS mRNA. The increased H-RAS mRNA levels were paralleled by inRAcreased H-Ras protein levels in about 90% of the cases. Interestingly, no differences were observed in H-RAS expression between nodules and adjacent nonnodular tissue in toxic nodular goiters (0.58+/-0.27 vs. 0.58+/-0.20 AU, P=0.88). None of the 10 samples from toxic multinodular goiters exhibited overexpression of H-RAS. The H-RAS expression was positively correlated with thyroglobulin expression (r2=0.51; P=0.04). In conclusion, we demonstrated increased levels of H-RAS mRNA and protein in samples of nontoxic multinodular goiter, indicating that it might be involved in goiter pathogenesis. In contrast, H-RAS overexpression was not detected in any of the samples of toxic multinodular goiter, suggesting different mechanisms for cell proliferation in nodular goiter according to thyroid status.

The presence of allele D of angiotensin-converting enzyme polymorphism is associated with diabetic nephropathy in patients with less than 10 years duration of Type 2 diabetes

AIM

To investigate the association between angiotensin-converting enzyme gene I/D polymorphism and diabetic nephropathy (DN) in patients with Type 2 diabetes mellitus (DM) taking into consideration the known duration of DM.

METHODS

Cross-sectional study with 982 patients categorized according to urinary albumin excretion (UAE) into normoalbuminuria (UAE < 20 microg/min or < 17 mg/l, 24-h timed urine or spot random sterile urine, respectively), incipient DN (UAE 20-199 microg/min or 17-174 mg/l) and overt DN (UAE > 200 microg/min or > 174 mg/l or dialysis). Patients were further grouped regarding presence of the D allele (DD/ID vs. II) and DM duration (< or = 10 years or > 10 years).

RESULTS

Incipient DN was diagnosed in 17.3% (n = 170), and 20.7% (n = 203) had overt DN (macroalbuminuria, n = 129; dialysis, n = 74). Genotype distribution (DD/ID/II) was similar in patients with incipient (49/92/29) or overt DN (77/89/37) if compared with patients without DN (181/308/120, P = 0.172). In patients with DM < or = 10 years, having the D allele (DD/ID) resulted in an odds ratio (OR) of 2.66 (95% CI: 1.12-6.58, P = 0.015) for incipient DN, and 3.19 (95% CI: 1.18-9.30, P = 0.012) for overt DN. In patients with longer DM duration, the D allele did not increase the risk for incipient (OR 0.68, 95% CI 0.36-1.29, P = 0.206) or overt DN (OR 0.67, 95% CI 0.39-1.17, P = 0.138).

CONCLUSION

The DD/ID genotypes were associated with incipient or overt DN in patients with DM < or = 10 years.

Hypothyroidism induces type 2 iodothyronine deiodinase expression in mouse heart and testis

In the present study we show the expression profiles of both type 1 and type 2 iodothyronine deiodinases (D1 and D2) in a wide spectrum of mouse tIssues, and D2 regulation by thyroid status. A characteristic tIssue-specific expression for each isoform was observed. D2 transcripts were detected in most tIssues with variable levels of expression. The observed D2 mRNA tIssue distribution was similar to that described in rats and is in agreement with the view of different patterns of expression between rodents and humans. However, it is interesting to note that despite the low levels of D2 transcripts in mouse heart and testis in the euthyroid state, the induction of hypothyroidism caused a significant increase in D2 activity in these tIssues. Similar results were also obtained in adult rats. These results suggest a previously unrecognized role for type 2 deiodinase in controlling intracellular triiodothyronine levels in rodent heart and testis during states of thyroid hormone deficiency.

Regulation of human endometrial transforming growth factor beta1 and beta3 isoforms through menstrual cycle and medroxyprogesterone acetate treatment

The progesterone-induced differentiation of endometrial tissue from proliferative into secretory and decidua seems to be modulated by locally produced hormones and cytokines. Transforming growth factor beta (TGFbeta). a cytokine produced by endometrial cells, has been shown to modulate endometrial cell proliferation in vitro. Our aim was to evaluate the effects of medroxyprogesterone acetate (MPA) and the influence of menstrual cycle on the expression of TGFbeta1 and TGFbeta3 in human endometrium in vivo. In a double-blind, placebo-controlled trial, 46 healthy women with regular menstrual cycles received either MPA (10 mg/day) or placebo during 10 days. Endometrial and blood samples were collected 8-12 hours after the last MPA or placebo administration. Patients were classified into three groups according to biopsy dating and treatment: proliferative [tissue]/placebo, secretory [tissue]/placebo and secretory [tissue]/MPA. The immunohistochemical distribution of TGFbeta1 and TGFbeta1 mRNA was similar in all groups. Immunoreactive TGFbeta3 was present in the epithelium in 9.1% of proliferative samples, in 41.2% of secretory/placebo samples and in 87.5% of secretory/MPA samples (p=0.001). In the stroma, the frequency of TGFbeta3 staining was markedly increased after treatment with MPA (62.5%) compared to placebo (proliferative: 9.1%; secretory: 5.9%; p=0.005). The levels of TGFbeta3 mRNA increased during the secretory phase and were higher in the MPA-treated group, being directly correlated with morphological endometrial differentiation. It is concluded that MPA administration to healthy women increased TGFbeta3 but did not change TGFbeta1 gene and protein expression in the endometrium. This finding suggests that TGFbeta3 may be a local factor mediating progesterone- and progestogen-induced endometrial differentiation.

The effect of methimazole pretreatment on the efficacy of radioactive iodine therapy in Graves' hyperthyroidism: one-year follow-up of a prospective, randomized study

The effect of antithyroid drugs on the efficacy of radioiodine (131I) treatment is still controversial. This study evaluated the effect of methimazole pretreatment on the efficacy of 131I therapy in Graves' hyperthyroidism. Sixty-one untreated patients were randomly assigned to receive 131I alone (32 patients) or 131I plus pretreatment with methimazole (30 mg/d; 29 patients). 131I was administered 4 d after drug discontinuation. The calculated 131I dose was 200 microCi/g thyroid tissue as estimated by ultrasound, corrected by 24-h radioiodine uptake. Serum TSH, T4, and free T4 were measured 4 d before 131I therapy, on the day of treatment, and then monthly for 1 yr. Considering cure as euthyroidism or hypothyroidism, based on free T4 measurement, approximately 80% of patients from both groups were cured 3 months after beginning 131I treatment. After 1 yr the groups were similar in terms of persistent hyperthyroidism (15.6% vs. 13.8%), euthyroidism (28.1% vs. 31.0%), or hypothyroidism (56.3% vs. 55.2%). Relapsed patients presented larger thyroid volume (P = 0.002), higher 24-h radioiodine uptake (P = 0.022), and T3 levels (P = 0.002). Multiple logistic regression analysis identified T3 values as an independent predictor of therapy failure. In conclusion, pretreatment with methimazole had no effect on either the time required for cure or the 1-yr success rate of 131I therapy.

Histoplasmosis of the thyroid

Fungal infection of the thyroid is rare. Most reported cases have involved Aspergillus, Coccidioides, and Candida species in the setting of disseminated disease. Infection of the thyroid with Histoplasma capsulatum is rarely reported as part of disseminated disease, even in geographic areas where histoplasmosis is endemic. We report a 52-year-old woman with a previous Hashimoto's disease and non-Hodgkin's lymphoma in which a diffuse enlarged thyroid gland with a large nodule was the only apparent locus of histoplasmosis. Fine-needle aspiration of the thyroid was an important diagnostic tool in establishing the diagnosis of histoplasmosis of the thyroid. The patient was initially treated with itraconazole (400 mg/day) for the fungal infection and six cycles of chemotherapy for the lymphoma. At a 6-month follow-up examination, the patient was doing well on suppressive therapy of itraconazole (200 mg/day), with no symptoms and with regression of the thyroid nodule and cervical adenopathy.

Effect of methimazole pretreatment on serum thyroid hormone levels after radioactive treatment in Graves' hyperthyroidism

Radioiodine (131I) is the preferred definitive treatment for Graves' hyperthyroidism. Pretreatment with antithyroid drugs is often used to avoid thyroid hormone discharge after 131I ablation. However, this may represent an unnecessary increase in risk and costs. Fifty-one patients with Graves' disease were randomly assigned to receive 131I alone (28 patients) or 131I plus pretreatment with methimazole (30 mg/day; 23 patients). Methimazole was interrupted 4 days before 131I therapy. Serum T4, free T4 (FT4), and T3 were measured on days -4 and -1, on the day of treatment, and on days 2, 5, 7, 14, 20, and 30. In patients receiving 131I alone, mean serum T4 levels did not change after therapy. Mean serum FT4 and T3 levels decreased significantly 5 days after 131I administration (15% and 18%, respectively). Serum T3 reached its lowest level on day 30 (38%). With pretreatment, mean serum T4, FT4, and T3 levels increased (38%, 39%, and 70%, respectively) after methimazole discontinuation and before 131I administration. After 131I, serum T4 levels peaked on day 7 (23% vs. treatment day; 70% vs. baseline); FT4 levels peaked on day 14 (53% vs. treatment day; 107% vs. baseline). The serum T3 concentration increased 9% on day 2 (85% vs. baseline) and decreased from day 14 (15%) to day 30 (21%). We conclude that interruption of antithyroid drugs causes a short term increase in serum thyroid hormone levels in patients with Graves' hyperthyroidism receiving 131I. Thyroid hormone levels stabilize or decrease during the first 30 days after 131I therapy.

Diagnosing dementia and normal aging: clinical relevance of brain ratios and cognitive performance in a Brazilian sample

The main objective of the present study was to evaluate the diagnostic value (clinical application) of brain measures and cognitive function. Alzheimer and multi-infarct patients (N = 30) and normal subjects over the age of 50 (N = 40) were submitted to a medical, neurological and cognitive investigation. The cognitive tests applied were Mini-Mental, word span, digit span, logical memory, spatial recognition span, Boston naming test, praxis, and calculation tests. The brain ratios calculated were the ventricle-brain, bifrontal, bicaudate, third ventricle, and suprasellar cistern measures. These data were obtained from a brain computer tomography scan, and the cutoff values from receiver operating characteristic curves. We analyzed the diagnostic parameters provided by these ratios and compared them to those obtained by cognitive evaluation. The sensitivity and specificity of cognitive tests were higher than brain measures, although dementia patients presented higher ratios, showing poorer cognitive performances than normal individuals. Normal controls over the age of 70 presented higher measures than younger groups, but similar cognitive performance. We found diffuse losses of tissue from the central nervous system related to distribution of cerebrospinal fluid in dementia patients. The likelihood of case identification by functional impairment was higher than when changes of the structure of the central nervous system were used. Cognitive evaluation still seems to be the best method to screen individuals from the community, especially for developing countries, where the cost of brain imaging precludes its use for screening and initial assessment of dementia.

Progestin modulation of c-fos and prolactin gene expression in the human endometrium

OBJECTIVE

To evaluate the influence of the menstrual cycle and the effects of medroxyprogesterone acetate (MPA) on the expression of the protooncogene c-fos and of prolactin (PRL) in the human endometrium in vivo.

DESIGN

Double-blind, placebo-controlled trial.

SETTING

Healthy volunteers in an academic research environment.

PATIENT(S)

Regularly cycling women who were not taking hormonal medication.

INTERVENTION(S)

Medroxyprogesterone acetate (10 mg/d) or placebo was given for 10 days. Endometrial and blood samples were collected 8-12 hours after the last dose.

MAIN OUTCOME MEASURE(S)

Immunohistochemical localization of PRL and c-fos in the endometrium, PRL and c-fos messenger RNA levels in the endometrium, and E2 and progesterone levels in the serum.

RESULT(S)

Immunoreactive c-fos was concentrated in the nucleus of stromal cells and was observed in a higher proportion of proliferative endometrial specimens compared with secretory specimens from placebo or MPA-treated patients. The levels of c-fos messenger RNA were greatly reduced in the secretory endometrium regardless of treatment with placebo or MPA, compared with the proliferative endometrium. The c-fos gene expression correlated positively with the serum E2 levels (r = 0.56) and inversely with the progesterone/E2 ratio (r = -0.56). The endometrial PRL gene expression (messenger RNA and protein) was rare in the proliferative samples, increased from the early to the mid and late secretory samples, and was increased markedly after treatment with MPA compared with placebo.

CONCLUSION(S)

The differentiation of secretory endometrium is accompanied by decreased c-fos and increased PRL gene expression. The inhibition of c-fos gene expression may contribute to the antiproliferative effect of progestins on the endometrium.

Is there a negative TRE in the luciferase reporter cDNA?

Transient expression assays using a luciferase (LUC) reporter gene are often used in studies of positive and negative thyroid hormone response elements (TREs) or of wild-type and mutated thyroid hormone receptors (TRs). However, unliganded TR (the beta isoform > than the alpha) increases LUC expression from 2 different TK-LUC vectors in several cell types, especially JEG-3 cells, and 3,5,3'-triiodothyronine (T3) reduces that expression by as much as 80% in a TR-dependent manner. The TR effects require an intact TR DNA-binding domain and the results suggest that there may be a negative TRE in the LUC cDNA. We conclude that great care must be used in the interpretation of studies of thyroid hormone action using LUC expression plasmids especially when these are performed in JEG-3 cells.

Effect of 3,5,3'-Triiodothyronine (T3) administration on dio1 gene expression and T3 metabolism in normal and type 1 deiodinase-deficient mice

The type 1 deiodinase (D1) catalyzes the monodeiodination of T4 to produce T3, the active thyroid hormone. In the C3H mouse, hepatic D1 and the dio1 messenger RNA (mRNA) are only 10% that in the C57 strain, the common phenotype. Low activity cosegregated with a series of five GCT repeats located in the 5'-flanking region of the C3H dio1 gene that impaired C3H promoter potency and provided a partial explanation for the lower D1. The present studies were performed to search for additional explanations for low D1 activity in C3H mice. Previous studies have shown that T3 up-regulates the dio1 gene. Therefore, loss of the capacity to respond to endogenous T3 is a possible additional cause of the lower D1 levels in the C3H mice. The hepatic C3H dio1 mRNA increases 10- to 20 fold after T3 administration. The t3 effect occurs at a transplantation level and T3 does not alter the dio1 mRNA half-life. Despite the transcriptional response to T3, no functional thyroid response elements were identified in the 1.5-kilobase 5'-flanking region of either the C57 or C3H dio1 gene. After the same dose of exogenous T3, both dio1 mRNA and D1 of the C3H mouse respond to a greater extent than those of the C57 strain. This can be explained in part by the reduction in T3 clearance due to the lower D1 levels in C3H mice in which higher concentrations of circulating T3 are maintained. The decrease in serum T3 levels and T3 production observed in fasting and systemic illness in both human and experimental animals has been attributed in part to a decrease in hepatic D1. In contrast, despite markedly lower hepatic and renal D1 levels, serum T3 concentrations remain normal in C3H mice. The present studies suggest that the absence of stress-induced hypothalamic-pituitary suppression that allows T4 production to be maintained together with the reduced clearance of T3 and T4 via inner ring deiodination compensate for the D1 deficiency.

Type 3 lodothyronine deiodinase: cloning, in vitro expression, and functional analysis of the placental selenoenzyme

Type 3 iodothyronine deiodinase (D3) catalyzes the conversion of T4 and T3 to inactive metabolites. It is highly expressed in placenta and thus can regulate circulating fetal thyroid hormone concentrations throughout gestation. We have cloned and expressed a 2.1-kb human placental D3 cDNA which encodes a 32-kD protein with a Km of 1.2 nM for 5 deiodination of T3 and 340 nM for 5' deiodination of reverse T3. The reaction requires DTT and is not inhibited by 6n-propylthiouracil. We quantitated transiently expressed D3 by specifically labeling the protein with bromoacetyl [125I]T3. The Kcat/Km ratio for 5 deiodination of T3 was over 1,000-fold that for 5' deiodination of reverse T3. Human D3 is a selenoenzyme as evidenced by (a) the presence of an in frame UGA codon at position 144, (b) the synthesis of a 32-kD 75Se-labeled protein in D3 cDNA transfected cells, and (c) the presence of a selenocysteine insertion sequence element in the 3' untranslated region of the mRNA which is required for its expression. The D3 selenocysteine insertion sequence element is more potent than that in the type 1 deiodinase or glutathione peroxidase gene, suggesting a high priority for selenocysteine incorporation into this enzyme. The conservation of this enzyme from Xenopus laevis tadpoles to humans implies an essential role for regulation of thyroid hormone inactivation during embryological development.

A novel retinoid X receptor-independent thyroid hormone response element is present in the human type 1 deiodinase gene

We identified two thyroid hormone response elements (TREs) in the 2.5-kb, 5'-flanking region of the human gene encoding type 1 iodothyronine deiodinase (hdio1), an enzyme which catalyses the activation of thyroxine to 3,5,3'-triiodothyronine (T3). Both TREs contribute equally to T3 induction of the homologous promoter in transient expression assays. The proximal TRE (TRE1), which is located at bp -100, has an unusual structure, a direct repeat of the octamer YYRGGTCA hexamer that is spaced by 10 bp. The pyrimidines in the -2 position relative to the core hexamer are both essential to function. In vitro binding studies of TRE1 showed no heterodimer formation with retinoid X receptor (RXR) beta or JEG nuclear extracts (containing RXR alpha) and bacterially expressed chicken T3 receptor alpha 1 (TR alpha) can occupy both half-sites although the 3' half-site is dominant. T3 causes dissociation of TR alpha from the 5' half-site but increases binding to the 3' half-site. Binding of a second TR to TRE1 is minimally cooperative; however, no cooperativity was noted for a functional mutant in which the half-sites are separated by 15 bp, implying that TRs bind as independent monomers. Nonetheless, T3 still causes TR dissociation from the DR+15, indicating that dissociation occurs independently of TR-TR contact and that rebinding of a T3-TR complex to the 3' half-site occurs because of its slightly higher affinity. A distal TRE (TRE2) is found at bp -700 and is a direct repeat of a PuGGTCA hexamer spaced by 4 bp. It has typical TR homodimer and TR-RXR heterodimer binding properties. The TRE1 of hdio1 is the first example of a naturally occurring TRE consisting of two relatively independent octamer sequences which do not require the RXR family of proteins for function.

Effects of thyroid hormone on norepinephrine signaling in brown adipose tissue. I. Beta 1- and beta 2-adrenergic receptors and cyclic adenosine 3',5'-monophosphate generation

Brown adipose tissue (BAT) thermogenesis is activated by the sympathetic nervous system. BAT responses to norepinephrine are blunted in hypothyroidism and are rapidly restored by thyroid hormone. We examined in rats the effects of thyroid hormone on BAT beta 1- and beta 2-adrenergic receptors (AR) expression and capacity to generate cAMP in response to adrenergic stimulation. Both are reduced in hypothyroidism. The reduction in cAMP generation is equal to or greater than that in beta 1,2-AR; it is the same whether cAMP production is stimulated with norepinephrine, selective beta 3-AR agonists, or forskolin; and it is not affected by the inhibition of phosphodiesterase. Both beta 1,2-AR and the capacity to generate cAMP were slowly corrected by thyroid hormone. T3 normalized beta 1,2-AR between 1 and 2 days, whereas the improvement in cAMP generation lagged 1 or 2 days behind. Within 2 days of acclimation of athyreotic rats at 30 C, the number of beta 1,2-AR reached the euthyroid level, whereas exposure to 4 C decreased these receptors. We reached the following conclusions: 1) BAT beta 1,2-AR and capacity to generate cAMP are reduced in hypothyroidism; 2) the latter, however, is not explained by the reduction in beta 1,2-AR, but, rather, reflects a fault at the postreceptor level; 3) the reduction in beta 1.2-AR number is largely caused by the cold stress derived from the low metabolic rate of the hypothyroid state; and 4) the slow restoration of both receptor number and capacity to generate cAMP after T3 are not consistent with these defects being a significant factor in the previously reported blunted uncoupling protein responses to adrenergic stimulation in hypothyroidism.

Structural and functional differences in the dio1 gene in mice with inherited type 1 deiodinase deficiency

The type 1 deiodinase (D1) provides the major portion of the circulating T3 in vertebrates. In C3H and certain other inbred mice, liver and kidney D1 activity is 5- to 10-fold lower than in the common phenotype, C57. The lower D1 levels are paralleled by a decreased normal-sized dio1 mRNA and hyperthyroxinemia. Low activity cosegregates with a restriction fragment length variant (RFLV) in both inbred and recombinant strains, indicating it is due to differences in the dio1 gene. The exonic structure and the deduced amino acid sequences are identical for both strains and highly homologous to that of the rat. The RFLV is due to an approximately 150-base pair expansion of repetitive sequences in the second intron of the C3H gene, but this segment does not differentially affect the transient expression of a human GH gene. The promoter and 5'-flanking regions of the C3H and C57 dio1 genes are very similar and are GC rich without TATA or CCAAT boxes. However, functional assays of 1.5-kilobase 5'-flanking dio1-CAT constructs showed 2- to 3-fold higher activity of the C57-CAT constructs. Deletion mutants showed that sequences between -705 and -162 were the cause of this. In this region, the only major difference between the two genes is a 21-base pair insert containing five CTG repeats in the C3H promoter. This difference also cosegregates with low D1 activity and the intron RFLV in four other mouse strains. The correlation of the CTG repeat insert with both in vitro and in vivo expression and the absence of other significant sequence differences in the 5'-flanking region argue that this is the major explanation for the impaired expression of the dio1 gene and the resulting hyperthyroxinemia of the C3H mouse.

Hypothyroidism affects pulsatile LH secretion in pubertal orchiectomized rats

The present study evaluated the effect of hypothyroidism on the pituitary-testicular axis in rats rendered hypothyroid on the beginning of puberty. Rats were treated with propylthiouracil for 8 weeks and killed for determination of hormonal status and body parameters. For determination of pulsatile LH secretion other animals were orchiectomized two weeks before sampling. Analysis of the results led us to conclude that although the absolute weight of sex organs tended to decrease in hypothyroid animals, the relative weights were equal or higher than control, suggesting that the development of these organs were not affected by hypothyroidism; the androgenic activity of hypothyroid rat testes were preserved; basal plasma levels of pituitary hormones were similar in control and hypothyroid groups; the pulsatile LH secretion showed a decrease in the number of pulses, nadir mean and total LH secretion in hypothyroid animals. Our results demonstrate that although hypothalamic-pituitary axis of hypothyroid pubertal rats displays an abnormal pulsation LH release, no evidences of abnormalities in the reproductive system functions were found.

Cloning and nucleotide sequence of a specific DNA fragment from Paracoccidioides brasiliensis

We cloned and sequenced a species-specific 110-bp DNA fragment from Paracoccidioides brasiliensis. The DNA fragment was generated by PCR with primers complementary to the rat beta-actin gene under a low annealing temperature. Comparison of the nucleotide sequence, after excluding the primers, with those in the GenBank database identified approximately 60% homology with an exon of a major surface glycoprotein gene from Pneumocystis carinii and a fragment of unknown function in Saccharomyces cerevisiae chromosome VIII. By Southern hybridization analysis, the 32P-labelled fragment detected 1.0- and 1.9-kb restriction fragments within whole-cell genomic DNA of P. brasiliensis digested with HindIII and PstI, respectively, but failed to hybridize to genomic DNAs from Candida albicans, Blastomyces dermatitidis, Cryptococcus neoformans, Aspergillus fumigatus, Saccharomyces cerevisiae, Pneumocystis carinii, rat tissue, or humans under low-stringency hybridization conditions. Additionally, the specific DNA fragment from three different P. brasiliensis isolates (Pb18, RP18, RP17) was amplified by PCR with primers mostly complementary to nonactin sequences of the 110-bp DNA fragment. In contrast, there were no amplified products from other fungus genomic DNAs previously tested, including Histoplasma capsulatum. To date, this is the first species-specific DNA fragment cloned from P. brasiliensis which might be useful as a diagnostic marker for the identification and classification of different P. brasiliensis isolates.

Pituitary cells respond to thyroid hormone by discrete, gene-specific pathways

Type 1 iodothyronine deiodinase (D1) converts T4 to T3, the active thyroid hormone, by removal of the outer ring iodine. Previous studies in liver and thyroid cells have shown that T3 regulates Type 1 deiodinase (dio1) gene expression by a mechanism not requiring ongoing protein synthesis. For certain T3-regulated genes, such as rat GH, T3-induced transcription is blocked by protein synthesis inhibitors. Because the somatotrope tumor cell lines express both dio1 and GH, we compared these two positively T3-regulated genes to establish whether cycloheximide blockade of T3 effects is cell-type or gene specific. In these cells, the T3 stimulation of dio1 messenger RNA (mRNA) is not blocked by cycloheximide, whereas the T3 effect on GH mRNA synthesis is eliminated. Other differences between these two genes were also noted. Retinoic acid does not alter dio1 gene expression or the response to T3 but increases GH and synergizes with T3. Dexamethasone alone had no effect on dio1 mRNA but did enhance the effect of T3 on both dio1 and GH. These results point to distinct pathways for T3 induction of mRNA synthesis from different genes within the same cell.

Physiological and genetic analyses of inbred mouse strains with a type I iodothyronine 5' deiodinase deficiency

Inbred mouse strains differ in their capacity to deiodinate iododioxin and iodothyronines, with strains segregating into high or low activity groups. Metabolism of iododioxin occurs via the type I iodothyronine 5'deiodinase (5'DI), one of two enzymes that metabolize thyroxine (T4) to 3,5,3'-triiodothyronine (T3). Recombinant inbred strains derived from crosses between high and low activity strains exhibit segregation characteristic of a single allele difference. Hepatic and renal 5'DI mRNA in a high (C57BL/6J) and low (C3H/HeJ) strain paralleled enzyme activity and concentration, in agreement with a recent report. 5'DI-deficient mice had twofold higher serum free T4 but normal free T3 and thyrotropin. Brown adipose tissue 5'DII was invariant between the two strains. Southern analyses using a 5'DI probe identified a restriction fragment length variant that segregated with 5'DI activity in 33 of 35 recombinant inbred strains derived from four different pairs of high and low activity parental strains. Recombination frequencies using previously mapped loci allowed assignment of the 5'DI gene to mouse chromosome 4 and identified its approximate chromosomal position. We propose the symbol Dio1 to denote the mouse 5'DI gene. Conserved linkage between this segment of mouse chromosome 4 and human HSA1p predicts this location for human Dio1.

Substitution of cysteine for selenocysteine in type I iodothyronine deiodinase reduces the catalytic efficiency of the protein but enhances its translation

Type I iodothyronine 5' deiodinase (5'DI) contains selenocysteine, encoded by a UGA codon, and this amino acid is essential for maximum catalytic efficiency in this enzyme. We recently showed that translation of UGA as selenocysteine in this protein requires a specific sequence of about 250 nucleotides in the 3' untranslated region of the messenger RNA. Translation of a 5'DI cysteine mutant does not require the 3' untranslated region. To examine both the efficiency of UGA codon recognition and the relative catalytic efficiency of selenocysteine vs. cysteine in 5'DI, we used bromoacetyl 125I-T3 labeling to quantitate transiently expressed selenocysteine (wild type) and cysteine containing type I iodothyronine deiodinases in transfected COS-7 and JEG-3 cell lines. Kinetic analyses of the same cell sonicates were performed to determine the apparent maximum velocity and Michaelis-Menten constant values for reverse T3 5' deiodination. COS-7 cells express the cysteine mutant protein at about 20-fold and JEG-3 cells about 400-fold higher levels than the selenoenzyme. However, in both cell types, the apparent catalytic constant values were at least 100-fold higher for the wild-type enzyme, compared with the cysteine mutant. These results indicate that cell lines differ markedly in their capacity to translate UGA-containing messenger RNAs. The much higher catalytic constant values for the selenium-containing enzyme illustrate the biochemical advantage of this element as compared with sulfur in the catalysis of iodothyronine deiodination.