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Biomedical subjects

C Ledent

Publications and source records attributed to C Ledent.

At least 73 records · Page 4Linked to original sources
PubMed1997

Costimulation of adenylyl cyclase and phospholipase C by a mutant alpha 1B-adrenergic receptor transgene promotes malignant transformation of thyroid follicular cells.

Proliferation of thyroid follicular cells is controlled by three intra-cellular cascades [cAMP, inositol 1,4,5-triphosphate (IP3)/Ca2+/diacylglycerol (DAG), and tyrosine kinases] that are activated by distinct extracellular signals and receptors. We had previously generated a transgenic mouse model in which the cAMP cascade was permanently stimulated in thyroid cells by an adenosine A2a receptor (Tg-A2aR model). In the present work, we have generated a transgenic model characterized by the chronic stimulation of both adenylyl cyclase and phospholipase C in thyroid follicular cells. The bovine thyroglobulin gene promoter was used to direct the expression of a constitutively active mutant of the alpha 1B adrenergic receptor, which is known to couple to both cascades in transfected cell lines. The expression of the transgene resulted, as expected, in the activation of phospholipase C and adenylyl cyclase, as demonstrated by the direct measurement of IP3 and cAMP in thyroid tissue. The phenotype resulting from this dual stimulation included growth stimulation, hyperfunction, cell degeneracy attributed to the overproduction of free radicals, and the development of malignant nodules invading the capsule, muscles, and blood vessels. Differentiated metastases were found occasionally in old animals. The development of malignant lesions was more frequent and of earlier onset than in our previous Tg-A2aR model, in which only the cAMP cascade was stimulated. These observations demonstrate that the cAMP and IP3/Ca2+/DAG cascades can cooperate in vivo toward the development of thyroid follicular cell malignancies.

Adenylyl Cyclases↗
PubMed1997

[Accelerated desensitization for hymenoptera venom allergy in 30 hours: efficacy and safety in 150 cases].

In this study, we performed 150 desensitizations in 139 Hymenoptera venom allergic patients (109 Yellow jacket allergic patients, 19 Honey bee allergic patients and 11 patients sensitized to both insects, who received a dual desensitization). We used a rush protocol, allowing injection of a total cumulated dose of 125,1 (Honey bee) to 175,1 (Yellow jacket) microgram of venom in 30 hours. Patients were hospitalized, with all emergency precautions for treating systemic reactions. The protocol was well tolerated in 147/150 cases; 3 patients had a benign systemic reaction. Patients received monthly maintenance doses of 100 micrograms venom. 39 patients experienced a field sting during immunotherapy; 2 of them (5%) had a benign systemic reaction. Thus, our rush desensitization protocol seems to be safe and effective.

Adolescent↗
PubMed1996

Early occurrence of metastatic differentiated thyroid carcinomas in transgenic mice expressing the A2a adenosine receptor gene and the human papillomavirus type 16 E7 oncogene.

We report here the characterization of a transgenic mouse model (Tg-A2aR/Tg-E7) resulting from the coexpression of two oncogenic transgenes in the thyroid. The two transgenes (Tg-A2aR and Tg-E7) were placed under control of the thyroid specific thyroglobulin gene promoter, and directed the expression of either the A2a adenosine receptor that constitutively activates the cAMP pathway, or the E7 protein of the human papillomavirus type 16, that binds and inactivates the retinoblastoma susceptibility gene product (Rb1). Transgenic mice expressing both transgenes were generated by interbreeding the Tg-A2aR and Tg-E7 transgenic lines, generated and characterized previously (Ledent et al., 1992, 1995). These mice develop a larger goiter than that of the two parental lines, and a severe hyperthyroidism comparable to that observed in the Tg-A2aR parental line. The main feature of the Tg-A2aR/Tg-E7 mice is the rapid occurrence of malignant lesions, and the dissemination of malignant thyroid tissue through the blood stream, generating multiple differentiated and functional metastases in the lung. These metastases appeared as early as 2 months after birth and their frequency increased to 75% over 3 months. They were associated with the presence of large vascular lakes in the thyroid. Electron microscopy of the malignant cells revealed nuclear features similar to those of human thyroid papillary carcinoma. These mice, in which two oncogenes are co-expressed in the thyroid, represent the first genetic animal model developing metastatic differentiated carcinomas of the thyroid with a high frequency.

Animals↗
PubMed1996

Thyroid pathologies in transgenic mice expressing a human activated Ras gene driven by a thyroglobulin promoter.

Four transgenic mice carrying the human activated c-Ha-Ras gene, the expression of which was driven into the thyroid gland by a bovine thyroglobulin promoter, have been produced. The M1 and M2 mice developed papillary thyroid carcinomas and the M2 mouse also developed a lung carcinoma, however none of them transmitted the transgene. Both the M3 and the M4 mice gave rise to transgenic lines. M3 progeny mice develop a goitre with morphological aspects of hyperplasia as well as a thymus hyperplasia. M4 developed a papillary thyroid carcinoma and a lung carcinoma. Lung tumors but not thyroid tumors were observed in M4 adult transgenic progeny. In this M4 line, thyroid dysgenesis leading to growth retardation and premature death was observed upon serial backcross that enhanced the DBA/2J genetic background. The development of thyroid tumors in M1, M2, M4 transgenic mice demonstrates the oncogenic potential of activated Ras gene in the thyroid gland. The M4 line raises interesting questions relative to the interference between the Ras-mediated signal transduction pathway and thyroid morphogenesis.

Animals↗
PubMed1996

Transgenic models for proliferative and hyperfunctional thyroid diseases.

Mouse transgenic models that develop thyroid diseases were generated. All transgenes were driven by the thyroid specific promoter of the thyroglobulin gene. The tissue specificity of the promoter was investigated by using the bacterial chloramphenicol acetyl transferase gene as reporter. The expression of an adenosine A2a receptor resulted in the permanent activation of the cAMP cascade. As a consequence, the transgenic mice developed severe hyperthyroidism and a large goiter, demonstrating in vivo the role of the cAMP cascade in the promotion of both function and proliferation of the thyroid cell. These mice constitute a model for autonomous hyperfunctional adenoma and non-autoimmune familial hyperthyroidism, where mutant thyrotropin receptors stimulate the cAMP cascade constitutively. In another transgenic model, the function of the retinoblastoma susceptibility gene product RB1 (and of related proteins) was inhibited by expression of the E7 oncoprotein of human papillomavirus type 16. The result was the development of a differentiated and normofunctional colloid goiter, with the progressive development of differentiated malignant lesions. This model suggests the essential role of RB1 and related proteins in the negative control of proliferation that characterizes thyroid cells in the adult. Other transgenic models of thyroid diseases are discussed.

Adenoma↗
PubMed1996

Targeted expression of the ret/PTC1 oncogene induces papillary thyroid carcinomas.

The ret/PTC oncogene, a rearranged form of the ret proto-oncogene, has been found to be restricted to human papillary thyroid carcinomas. This report shows that transgenic mice with thyroid-targeted expression of the ret/PTC1 oncogene developed thyroid carcinomas with considerable similarities to human papillary thyroid carcinomas, particularly in the nuclear cytologic features and the presence of local invasion. Our findings indicate that ret/PTC2 is not only a biomarker associated with papillary thyroid carcinomas, but is also the only proven specific genetic event leading to the development of papillary thyroid carcinoma.

Animals↗
PubMed1996

[Asthma to green coffee of environmental origin].

A case of rhinitis and environmental asthma caused by unroasted coffee has been reported in an adolescent living in a building in which there is an installation for roasting coffee. The diagnosis, suggested by the case history, is confirmed by the presence of specific IgE, by the positive result of the skin test using unroasted coffee extract and also of a broncho-provocation test entailing the manipulation of dust from the coffee roasting room. An amelioration of the room and work conditions is recommended.

Adolescent↗
PubMed1996

[Transgenic models of human thyroid pathologies: hyperfunctional adenoma, anaplastic cancer, differentiated cancer, hypothyroidism].

Bovine thyroglobulin gene upstream regulatory sequences were used as a tissue specific promoter in order to direct the expression of different genes specifically to the thyroid gland. Transgenic models of thyroid diseases have been generated, by directing the expression of specific oncogenes to the thyroid cell. In one of these models (TgAgT), the sv40 large T antigen promoted the development of an aggressive undifferentiated tumor mimicking the phenotype of the human anaplastic carcinoma. In the second model (TgA2aR), the expression of the adenosine A2 alpha receptor, acting as a constitutive activator of adenylyl cyclase, resulted in the development of a hyperfunctioning goiter, and in old animals to the formation of malignant foci. Transgenic lines expressing the E6 oncogenic (TgE6) from type 16 human papillomavirus appeared to be asymptomatic. In contrast, the thyroid cells of mice expressing E7 oncogene divide very rapidly, but remain differentiated, resulting in the development of huge colloid goiters. Signs of malignancy appear late in the development. The molecular properties of E6 and E7 oncogenes are to bind, and inactivatc, the tumor suppressor gene producers p53 (E6), or RB (E7). Our transgenic models indicate that the RB protein (and/or related proteins) are essential factors in the negative control of thyroid cell proliferation. On the contrary, inactivation of p53 seems to play a minor role, at least in the early steps of tumor formation. In the last model (Tg alpha 1B), the expression of a mutant of the alpha 1B adrenergic receptor reported to activate both CAMP and sigma P3-CA-cascades, resulted in growth stimulation, hyperfunction, cell degeneracy attributed to the overproduction of free radicals and malignancy.

Animals↗
PubMed1995

Differentiated carcinomas develop as a consequence of the thyroid specific expression of a thyroglobulin-human papillomavirus type 16 E7 transgene.

The oncogenic properties of the high risk human papillomaviruses (HPV) E7 protein are attributed to its interaction with the retinoblastoma susceptibility gene product RB1 and other related proteins. We report here the generation of a transgenic model expressing the E7 oncogene of HPV16 in thyroid follicular cells, under control of the bovine thyroglobulin gene promoter. Transgenics develop differentiated and functionally regulated thyroid goitres, due to thyroid cell proliferation and accumulation of colloid. On the background of this colloid goitre, the mice develop foci of more actively proliferating cells that become invasive and ultimately tend to loose their differentiation. Old mice display secondary tumour nodules that mimic the various histological aspects of the human differentiated thyroid cancers: the follicular and papillary carcinomas. The development of totally undifferentiated carcinoma is in contrast exceptional. We conclude that RB1, and/or related proteins, are responsible for the strict negative control of proliferation that characterizes the thyroid cell of the adult. Inactivation of these proteins results in a continuous growth of the thyroid, without affecting its differentiation, function and regulation. Given the high frequency of progression to highly malignant phenotypes, the retinoblastoma susceptibility and related genes are good candidates as targets for mutations or deletions in early steps of human thyroid carcinogenesis. The search for such mutations in human thyroid cancers will test if this hypothesis holds true.

Animals↗
PubMed1994

Molecular genetics of thyroid diseases.

Over the past 20 years, recombinant deoxyribonucleic acid technology has led to the cloning of three major thyroid specific protein genes (thyroglobulin, thyroperoxidase and thyrotrophin receptor), which happen to be also the main thyroid autoantigens implicated in thyroid diseases. In this context, the impact that molecular genetics has had on the understanding of aetiopathogeny and diagnosis of thyroid diseases is summarized, with special emphasis on a recently discovered genetic mechanism responsible for toxic nodules. One fruitful outcome of the basic research on thyroid-specific gene expression has been the possibility of targeting the expression of a series of genes to the thyroid in transgenic mice. The result is the availability of mouse models mimicking human thyroid diseases such as destructive hypothyroidism, hyperactive thyroid adenomas and thyroid cancers exhibiting varying levels of differentiation.

Animals↗
PubMed1992

Expression of members of the putative olfactory receptor gene family in mammalian germ cells.

A series of genomic and complementary DNA clones encoding new putative members of G protein-coupled receptors were isolated using homology cloning and low-stringency polymerase chain reaction. Among the unidentified receptors ('orphan receptors'), a human genomic clone (HGMP07) was characterized by the presence of its transcripts in the testis and by its belonging to a large subfamily of genes sharing extensive sequence similarities. Sequence comparison demonstrated that this gene subfamily is the human counterpart of the putative rat olfactory receptors cloned recently. Another 48 members of the family were cloned. Northern blotting further demonstrated the presence of olfactory receptor transcripts in germ cells. Our finding suggests that a common receptor gene family encodes olfactory receptors and sperm cell receptors that could be involved in chemotaxis during fertilization.

Amino Acid Sequence↗
PubMed1992

Thyroid expression of an A2 adenosine receptor transgene induces thyroid hyperplasia and hyperthyroidism.

Cyclic AMP (cAMP) is the major intracellular second messenger of thyrotropin (TSH) action on thyroid cells. It stimulates growth as well as the function and differentiation of cultured thyrocytes. The adenosine A2 receptor, which activates adenylyl cyclase via coupling to the stimulating G protein (Gs), has been shown to promote constitutive activation of the cAMP cascade when transfected into various cell types. In order to test whether the A2 receptor was able to function similarly in vivo and to investigate the possible consequences of permanent adenylyl cyclase activation in thyroid cells, lines of transgenic mice were generated expressing the canine A2 adenosine receptor under control of the bovine thyroglobulin gene promoter. Thyroid-specific expression of the A2 adenosine receptor transgene promoted gland hyperplasia and severe hyperthyroidism causing premature death of the animals. The resulting goitre represents a model of hyperfunctioning adenomas: it demonstrates that constitutive activation of the cAMP cascade in such differentiated epithelial cells is sufficient to stimulate autonomous and uncontrolled function and growth.

Adenosine↗