Death-associated protein 3 is overexpressed in human thyroid oncocytic tumours.

BACKGROUND: The human death-associated protein 3 (hDAP3) is a GTP-binding constituent of the small subunit of the mitochondrial ribosome with a pro-apoptotic function. METHODS: A search through publicly available microarray data sets showed 337 genes potentially coregulated with the DAP3 gene. The promoter sequences of these 337 genes and 70 out of 85 mitochondrial ribosome genes were analysed in silico with the DAP3 gene promoter sequence. The mitochondrial role of DAP3 was also investigated in the thyroid tumours presenting various mitochondrial contents. RESULTS: The study revealed nine transcription factors presenting enriched motifs for these gene promoters, five of which are implicated in cellular growth (ELK1, ELK4, RUNX1, HOX11-CTF1, TAL1-ternary complex factor 3) and four in mitochondrial biogenesis (nuclear respiratory factor-1 (NRF-1), GABPA, PPARG-RXRA and estrogen-related receptor alpha (ESRRA)). An independent microarray data set showed the overexpression of ELK1, RUNX1 and ESRRA in the thyroid oncocytic tumours. Exploring the thyroid tumours, we found that DAP3 mRNA and protein expression is upregulated in tumours presenting a mitochondrial biogenesis compared with the normal tissue. ELK1 and ESRRA were also showed upregulated with DAP3. CONCLUSION: ELK1 and ESRRA may be considered as potential regulators of the DAP3 gene expression. DAP3 may participate in mitochondrial maintenance and play a role in the balance between mitochondrial homoeostasis and tumourigenesis.

[Spermatozoon mitochondrial DNA]. / ADN mitochondrial du spermatozoïde.

Mitochondria play a primary role in cellular energetic metabolism, homeostasis and death. In spermatozoa, in particular, mitochondria produce the ATP necessary for motility. Mitochondrial functions depend, at least partially, on mitochondrial DNA (mtDNA). The mitochondrial genome, the transmission of which is exclusively maternal contributes to cytoplasmic heredity. Qualitative and quantitative mtDNA abnormalities have been associated with male infertility. This review focuses on the role of mtDNA in human fertility.

[Energy metabolism of the cancer cell: example of mitochondria-rich endocrine tumors]. / Métabolisme énergétique de la cellule cancéreuse: exemple des tumeurs endocrines riches en mitochondries. Conférence donnée lors de la réunion annuelle du GTE Angers--17 novembre 2005.

Most solid tumours preferentially develop glycolytic metabolism, often accompanying tumor aggressiveness. Increase in nucleic acid synthesis is associated with cell proliferation and glucose shunting to the pentose phosphate pathway. High glucose consumption is more associated with a metabolic adaptation than with a mitochondrial defect. Tumor cells do not present specific genetic modifications but adapt their metabolic capacities to their priority needs. However their metabolisms depend on oncogene expression more specifically expressed in this context. The glycolytic pathway is favored by tumor proliferation under hypoxia. Stabilization of HIF1 factor may explain the glycolytic metabolism of the tumors in an anaerobic environment. We demonstrate in two types of mitochondrial rich tumors, that specific defects induce completely different metabolic directions: when familial paragangliomas present a glycolytic metabolism, thyroid oncocytic tumors develop a specific oxidative metabolism.

[An OPA3 gene mutation is responsible for the disease associating optic atrophy and cataract with extrapyramidal signs]. / Atrophie optique, cataracte et signes extra-pyramidaux par mutation du gène OPA3.

INTRODUCTION: In 1961, Garcin et al. described a family with several members affected with optic atrophy associated with cataract, and neurological symptoms. The authors believed this condition to be distinct from other diseases known at that time, e.g. the Behr syndrome, Marinesco-Sjogren syndrome and Friedreich's ataxia. METHOD: This family was followed over a period of 40 years and genes known to be responsible for optic atrophy were sequenced. RESULTS: The G277A mutation of OPA3 gene was responsible for this familial disease. DISCUSSION: A new clinical entity is identified: autosomal dominant optic atrophy and cataract, due to a heterozygous mutation of the OPA3 gene, a nuclear gene encoding a mitochondrial protein.

Defective mitochondrial ATP synthesis in oxyphilic thyroid tumors.

Oxyphilic tumors (oncocytomas or Hürthle cell tumors) form a rare subgroup of thyroid tumors characterized by cells containing abundant mitochondria. The relationship between the mitochondrial proliferation and the pathogenesis of these tumors is unknown. We have assessed the expression of the mitochondrial ND2 and ND5 (subunits of the nicotinamide adenine dinucleotide dehydrogenase complex) genes and the nuclear UCP2 (uncoupling protein 2) gene in 22 oxyphilic thyroid tumors and matched controls. The consumption of oxygen in mitochondria from tumors was determined by polarography. ATP assays were used to explore the mitochondrial respiratory chain activity and the oxidative phosphorylation coupling in seven fresh thyroid tumors and controls. Adenosine triphosphate synthesis was significantly lower in all the tumors, compared with controls, suggesting that a coupling defect in oxidative phosphorylation may be a cause of mitochondrial hyperplasia in oxyphilic thyroid tumors.

Analysis of Tg transcripts by real-time RT-PCR in the blood of thyroid cancer patients.

Serum Tg (sTg) assays are sometimes unsatisfactory for monitoring thyroid cancer because interference caused by anti-Tg antibodies may reduce the sensitivity of the tests during thyroid hormone therapy. We have therefore developed a complementary method using real-time quantitative RT-PCR based on the amplification of Tg mRNA. Two different pairs of primers were used for the determination of the frequency of one of the variants of the alternative splicing of Tg mRNA. The frequency of this variant was as high in patients (n = 40) as in controls (n = 30), accounting for about 33% of the total Tg mRNA. Using appropriate primers, we observed that Tg mRNA values in controls varied according to the volume of thyroid tissue and the TSH concentration. The Tg mRNA values allowed the definition of a positive cutoff point at 1 pg/microg total RNA. This cutoff point, tested on the group of patients treated for thyroid cancer, produced fewer false negative results than those obtained with sTg assays. The standardized, highly sensitive real-time RT-PCR technique may therefore prove useful as a complement to sTg assays, particularly for patients with recurrent thyroid cancer receiving T(4) therapy.

mtDNA haplogroup J: a contributing factor of optic neuritis.

Optic neuritis frequently occurs in multiple sclerosis (MS), and shares several similarities with the optic neuritis of Leber's hereditary optic neuropathy (LHON), which is mainly due to maternally transmitted mitochondrial DNA (mtDNA) mutations. Our report shows for the first time that a mitochondrial DNA background could influence the clinical expression of MS. One European mtDNA haplogroup was found only in MS patients with optic neuritis but not in MS patients without visual symptoms. Therefore, we hypothesize that mtDNA haplogroup J might constitute a risk factor for optic neuritis occurrence when it is coincidentally associated with MS, but not be a risk factor for developing MS per se as suggested previously.

Epitope mapping of human thyroglobulin reveals a central immunodominant region.

Thyroglobulin is the thyroid hormone precursor and the major antigen frequently involved in autoimmune diseases. The primary structure of human thyroglobulin is known but the spatial structure remains largely undetermined. By using fusion protein produced in prokaryotic system we have characterized seven short immunoreactive peptides carrying at least one epitope. None of them includes hormonogenic sites, but five are concentrated in the central part of the monomeric molecule, which thus emerges as the major immunogenic region of this protein.

Precursor-product relationship between the 26-kDa and 18-kDa fragments formed by iodination of human thyroglobulin.

At moderate iodination levels (20 iodine at atoms/molecule), human thyroglobulin (hTgb) produces after reduction a thyroxinyl-peptide of 26 kDa which represents the N-terminal part of the protein. At higher iodination levels, the 26-kDa peptide is accompanied by another T4-containing peptide of 18 kDa. A precursor-product relationship between the 26- and 18-kDa fragments was demonstrated by the study of the tryptic fragments of both hormonopeptides. In addition, comparison with the protein sequence deduced from the nucleotide sequence of the 5'-end of hTgb mRNA demonstrated that the N-terminal region of Htgb from which are issued the 26-kDa peptide and its 18-kDa derivative is especially sensitive to proteolysis. This character is possibly related with a facilitated release of thyroid hormones in vivo.

Thyroglobulin structure and function: recent advances.

Thyroglobulin is a large-size iodoglycoprotein specific to thyroid tissue and is the substrate for the synthesis of thyroid hormones, thyroxine and 3,5,3'-triiodothyronine. Recent studies, which greatly benefited from recombinant DNA methodologies, improved the knowledge of several structural features of this dimeric protein and permitted insights into some structure-function relationships. Analysis-function of the primary structure of the human thyroglobulin monomer revealed several main characteristics: 1) 3 types of internal homologies; 2) extensive homology with the bovine thyroglobulin monomer and known partial sequences in the thyroglobulins of other mammalian species; 3) significant homologies with 2 other non-thyroid proteins (acetylcholinesterase and the invariant chain of the Ia class II histocompatibility antigen); 4) a terminal localization of the hormonogenic sites at both ends of the monomer. Current studies aim at determining conformational characteristics, understanding the molecular mechanisms of thyroid hormone formation and unraveling those interactions which in the thyroid cell and the thyroid follicle will permit this large pro-hormone to synthesize and release a few small thyroid hormone molecules. A more precise knowledge of this molecule in higher vertebrates and during evolution would impart valuable information concerning thyroid pathology, since thyroglobulin has been implicated in some genetic and in autoimmune thyroid diseases.

Possible involvement of the dopamine D3 receptor locus in subtypes of bipolar affective disorder.

The dopamine D3 receptor gene is of potential interest in the physiopathology of affective disorder because of its expression pattern in brain structures controlling various aspects of behaviour, cognition and emotions. Moreover, it encodes for a receptor protein that is a target for psychotropic drugs, which turn out to be efficient in the treatment of this disorder. Two polymorphisms have been described at this locus (the Bal I and the Msp I Restriction Fragment Length Polymorphisms) that are useful in genetic studies. We therefore researched these polymorphisms in 60 patients suffering from bipolar affective disorder who were compared with 60 healthy volunteers. No statistical difference was observed between the whole patient sample versus the controls. However, one subgroup [homozygous for the (2-2) Bal I polymorphism] exhibits a characteristic clinical pattern consisting of: manic monopolar form of bipolar disorder, low age of onset and initiation by an acute delusional episode. A gender distribution difference for the Bal I polymorphism (chi 2 = 6.61, degrees of freedom = 1, P = 0.01) was then noted, the bipolar females being preferentially heterozygous, and the males homozygous. These results could involve the dopamine D3 receptor locus as a minor effect gene in the manic depression condition.

Mitochondrial activity in XTC.UC1 cells derived from thyroid oncocytoma.

Thyroid oncocytoma is characterized by the presence of oncocytes containing abnormally large numbers of mitochondria. However, the relationship between the abundance of mitochondria and the pathogenesis of the tumors is unknown. Recently, a new cell line, named XTC.UC1, has been derived from a metastasis of thyroid oncocytoma. We have studied the metabolism and the gene expression profile of the mitochondria in XTC.UC1 cells, using B-CPAP cells as controls. There were no signs of mitochondrial respiratory chain defects or uncoupling between the respiratory chain and adenosine triphosphate (ATP) production. In XTC.UC1 cells, mtDNA transcripts were increased more than fivefold than in controls, in parallel with a 3.6-fold increase in mtDNA content. Finally, in spite of the glycolytic metabolism induced by the culture medium, the mitochondria of XTC.UC1 cells possess the phenotype of oncocytic cells with hypertrophic mitochondria, higher respiratory enzyme activity and higher mtDNA content than in controls. XTC.UC1 cells may therefore offer a useful model for investigating the coordination of the nuclear and mitochondrial genomes, in the context of thyroid tumors.

No evidence of thyrotropin receptor and G(s alpha) gene mutation in high iodine uptake thyroid carcinoma.

Usually, thyroid carcinoma presents as a cold nodule on radioiodine scintigraphy. High-uptake nodules on iodine thyroid scans are associated with an exceedingly low incidence of malignancy. Only 29 cases of carcinomas appearing as hot or warm nodules have as yet been reported. From 1993 to 1999, we have observed eight similar cases (4 hot and 4 warm thyroid nodules) suggesting that thyroid carcinomas may not be as rare as usually considered in these circumstances. Four tumors were available for molecular analysis on paraffin-embedded sections. Because no mutations were found in the whole coding portions of thyrotropin-receptor (TSH-R) gene and fragments encompassing the mutational hot spots of the G(s alpha) gene, it is unlikely that activating mutations of the TSH-R or G(s alpha) genes were involved in these carcinomas.

Effects of changes in water compartments on physiology and metabolism.

There is paramount evidence to suggest the importance of cell volume changes for the regulation of cell function, including protein metabolism. Among many other effects, cell swelling inhibits proteolysis and stimulates protein synthesis. However, most of the data pertinent to this theory relate to in vitro experiments. This paper reviews the evidence about the relevance of cell swelling and changes in water compartments to regulation of metabolism at the whole body level in animals and humans. Protein metabolism is most likely regulated by cellular hydration in health and disease. Cellular hydration appears to bear no effect on energy metabolism. The relationship between cellular hydration and lipolysis deserves to be verified. There appears to be a possible weak effect on glucose metabolism. Further studies are therefore necessary to challenge the cell swelling theory. If confirmed, strategies to modify cellular hydration could be used to improve metabolic orientations especially in the critically ill.

Effect of the nonenzymatic glycosylation of high density lipoprotein-3 on the cholesterol ester transfer protein activity.

This study examines the relationship between high density lipoprotein-3 (HDL-3) glycation and cholesteryl ester transfer mediated by cholesteryl ester transfer protein (CETP). HDL-3 were glycated with various glucose concentrations (0-200 mM) for 3 d at 37 degrees C with sodium cyanoborohydride as reducing agent and antioxidants. About 47% of the lysine residues were glycated in the presence of 200 mM glucose, resulting in an increase in the cholesterol ester (CE) transfer of about 30%. Apparent kinetic parameters [expressed as maximal transfer (appT(max)) and CE concentration at half of T(max)(appK(H))] of CETP activity with glycated HDL-3 showed conflicting and paradoxical data: an increase in CETP activity associated with a decrease of CETP affinity. These alterations were not due to a change in HDL-3 lipid and protein composition nor to a peroxidative process but were associated with an increase in HDL-3 electronegativity and a decrease of HDL-3 fluidity. This study suggests that glycation modifies the apolipoprotein's conformation and solvation which are major determinants of interfacial properties of HDL-3. These modifications in turn affect CETP reactivity.

[Thyroid hormones and obesity]. / Hormones thyroïdiennes et obésité

Although the stimulating effect of thyroid hormones on energy metabolism has been recognized for more than a century, the relation between thyroid function and weight control and obesity remains unclear. We review here the effects of thyroid hormones, hyperthyroidism, and hypothyroidism on body composition and the parameters of energy metabolism.

Microarray analysis refines classification of non-medullary thyroid tumours of uncertain malignancy.

Conventional histology failed to classify part of non-medullary thyroid lesions as either benign or malignant. The group of tumours of uncertain malignancy (T-UM) concerns either atypical follicular adenomas or the recently called 'tumours of uncertain malignant potential'. To refine this classification we analysed microarray data from 93 follicular thyroid tumours: 10 T-UM, 3 follicular carcinomas, 13 papillary thyroid carcinomas and 67 follicular adenomas, compared to 73 control thyroid tissue samples. The diagnosis potential of 16 selected genes was validated by real-time quantitative RT-PCR on 6 additional T-UM. The gene expression profiles in several groups were examined with reference to the mutational status of the RET/PTC, BRAF and RAS genes. A pathological score (histological and immunohistochemical) was estimate for each of the T-UM involved in the study. The correlation between the T-UM gene profiles and the pathological score allowed a separation of the samples in two groups of benign or malignant tumours. Our analysis confirms the heterogeneity of T-UM and highlighted the molecular similarities between some cases and true carcinomas. We demonstrated the ability of few marker genes to serve as diagnosis tools and the need of a T-UM pathological scoring.