[The iodine pathways within the thyroid gland: physiological aspects].
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Humans↗
Biomedical subjects
B Rousset
Publications and source records attributed to B Rousset.
Signaling from epithelial to dendritic cells of the thyroid gland: evidence for thyrocyte-derived factors controlling the survival, multiplication, and endocytic activity of dendritic cells.
Intrathyroidal dendritic cells (DC) isolated at the same time and then cultured with thyrocytes in the presence of thyrotropin (TSH) keep a phenotype of immature DC (Croizet et al, 2000). As DC from other sources are known to undergo a rapid maturation in vitro, we hypothesized that the maintenance of thyroid-derived DC in an immature state might be caused by thyrocytes-DC interactions. In this study, we investigated whether thyroid-derived DC could change their phenotype in response to TSH stimulation of thyrocytes. Over an 8-day period of culture, the population of DC increased 2- to 3-fold in the presence of TSH and decreased by more than 75% in the absence of TSH. The increase in the DC population was related to DC proliferation, whereas the reduction of the number of DC was secondary to a loss of cell-substrate adhesion and subsequent cell death. In the presence of TSH, DC acquired and maintained a high capacity for internalizing labeled ligands, expressed the mannose receptor, and exposed MHC class II molecules at the cell surface. On the contrary, DC cultured without TSH were devoid of endocytic activity and mannose receptor and, after 2 days, no longer exposed MHC class II molecules at the cell surface. Using conditioned media and enriched DC populations, we show that thyrocytes, in response to TSH, produce soluble factors capable of activating proliferation and endocytic activity of DC. Exogenous granulocyte/macrophage-colony stimulating factor and transforming growth factor-beta, known to be produced by thyrocytes, reproduced the effects of conditioned media. These data, giving evidence of a hormone-regulated signaling process between epithelial and dendritic cells in vitro, suggest that thyrocytes could promote the maintenance of a population of immature DC within the thyroid gland.
Animals↗
The expression of the sodium/iodide symporter is up-regulated in the thyroid of fetuses of iodine-deficient rats.
Is the fetal thyroid already capable to increase its iodide uptake in response to iodine deficiency? To answer this question, we analyzed the expression of the Na(+)/I(-) symporter and several other genes in the thyroid of rat fetuses at 21 d of gestation from control mothers presenting a mild or more severe iodine deficiency. Female rats were placed on a low iodine diet, not supplemented, or supplemented with iodide or perchlorate for 3 months. The maternal and fetal thyroidal iodide uptake was measured 24 h after injection of 10 microCi Na (125)I into the dams. The absolute iodide uptake of the maternal thyroid was unchanged in a low iodine diet, not supplemented, compared with one supplemented with iodide. In contrast, the fetal thyroid absolute iodide uptake of a low iodine diet, not supplemented, and one supplemented with perchlorate was decreased by 70% and 95% compared with that supplemented with iodide. Na(+)/I(-) symporter mRNA was detected in the fetal thyroid of supplemented with iodide and increased about 2- and 4- fold in the thyroid of fetuses from a low iodine diet, not supplemented, and one supplemented with perchlorate, respectively. Na(+)/I(-) symporter expression was induced in the fetal side of the placenta in both a low iodine diet, not supplemented, and one supplemented with perchlorate; in contrast, Na(+)/I(-) symporter mRNA was never detected in the maternal side of the placenta. Fetal thyroid thyroglobulin and type I deiodinase mRNA contents were only significantly increased with a diet supplemented with perchlorate. Glucose transporter 4 mRNA was decreased in the fetal thyroid of both a low iodine diet, not supplemented, and one supplemented with perchlorate compared with one supplemented with iodide. In conclusion, although the up-regulation of Na(+)/I(-) symporter expression in fetal thyroid and placenta in the low iodine diet, not supplemented group did not lead to restoration of a normal absolute iodide uptake, our data show that all adaptive and/or defending mechanisms against iodine deficiency are already present in the fetus.
Animals↗
Connexin 32 fused to the green fluorescent protein retains its ability to control the proliferation of thyroid cells.
Cell-to-cell exchanges of signaling molecules are thought to be involved in the control of cell proliferation. Connexins, which are encoded by a family of genes expressed in a cell type-specific manner, are considered as tumor suppressors. Thyroid epithelial cells co-express connexin 32 (Cx32) and connexin 43 (Cx43) that form distinct and delocalized gap junctions in vivo. The communication-deficient rat thyroid-derived cell lines, FRTL-5 and FRT, stably transfected with the Cx32 cDNA, have a reduced proliferation rate related to a prolonged G1 cell cycle phase. To determine whether Cx32-gap junctions exert the same regulatory role in vivo, we have undertaken a program of production of transgenic mice over-expressing Cx32 specifically in thyrocytes. To this purpose, we designed a vector in which the Cx32 cDNA was fused to the gene encoding the enhanced green fluorescent protein (EGFP) and placed under the control of a strong and thyroid-specific promoter, the thyroglobulin gene promoter (pTg). In stably transfected FRTL-5 cells, the Cx32/EGFP chimeric protein forms functional gap junction channels and induces the same proliferation slowdown as native Cx32. The pTg-Cx32/EGFP construct should thus allow us to obtain the thyroid-targeted over-expression of Cx32 in the mouse to investigate the involvement of Cx32-gap junctions in thyroid growth, functional activity and propensity to form tumors.
Animals↗
Culture of dendritic cells from a nonlymphoid organ, the thyroid gland: evidence for TNFalpha-dependent phenotypic changes of thyroid-derived dendritic cells.
Because they are sparsely distributed in tissues, dendritic cells (DC) present in nonlymphoid organs are difficult to isolate. Only DC from skin and lung have been successfully studied in culture. The objective of the present work was to investigate the possibility of isolating and culturing DC from an endocrine organ, the thyroid gland, which is particularly susceptible to the development of autoimmune processes. The study was conducted on pig thyroid glands to have sufficient amounts of starting material. This choice required the characterization of immunological reagents capable of recognizing DC markers in the pig species. Using a discontinuous trypsinization procedure, a DC population representing 2% to 3% of the thyroid cell suspension was reproducibly obtained. Isolated DC quantitatively attached to tissue culture-treated dishes and segregated from thyrocytes. DC identified as cells expressing major histocompatibility complex class II molecules, the mannose receptor, and the S100 protein were found to have a high capacity to internalize labeled ligands, dextran, and mannosylated albumin. These cells had a phenotype of immature DC. Secondarily, a fraction of DC detached from culture dishes, and floating DC had low or no endocytic activity, a characteristic of mature DC. Treatment of DC/thyrocytes cocultures with tumor necrosis factor alpha (TNFalpha) activated the transformation of immature DC into mature DC. These data show that DC isolated from the thyroid gland can be maintained immature or activated to undergo maturation in primary culture. The procedure of cell isolation and culture should be adaptable to human thyroid tissue for in vitro analyses of DC-mediated immune responses.
Animals↗
Formation of three-dimensional thyroid follicle-like structures by polarized FRT cells made communication competent by transfection and stable expression of the connexin-32 gene.
Pig thyrocytes, either in the intact gland or cultured under conditions leading to thyroid follicle reconstitution, coexpress two gap junction proteins, connexin-32 (Cx32) and connexin-43 (Cx43). As thyrocytes cultured in the form of a monolayer only express Cx43, we hypothesized that Cx32 could play a role in thyroid folliculogenesis. In the present work, we analyzed the ability of polarized FRT cells (that are gap junction deficient) to form follicle-like structures after stable transfection with either Cx32 or Cx43 genes. Wild-type and transfected FRT cells, while growing, showed the capacity to form three-dimensional structures corresponding to domes that result from the accumulation of fluid underneath limited areas of the cell layer. The number of domes formed by FRT cells expressing Cx32 (FRT-Cx32) was 2- to 3-fold higher than that obtained with either wild-type or Cx43-transfected FRT cells (FRT-Cx43). Domes generated by FRT-Cx32 cells were stable (beyond 3 weeks of culture), whereas those formed from wild-type or FRT-Cx43 cells were transient, disappearing when cells reached confluence. Inspection of the cell organization within domes formed from FRT-Cx32 cells by phase contrast and confocal microscopy revealed a progressive transition from domes toward closed structures with a lumen. The tightness of the lumen was demonstrated by the retention of a fluorescent probe, lucifer yellow, introduced by microinjection. Electron microscope examinations showed that the neoformed follicle-like structures had an inside-out polarity. Analyses of cell motion and division with time, by fluorescence video microscopy, indicated that the transformation of domes into inside-out follicles brings into play the migration of cells and, to a lesser extent, cell multiplication underneath the domes. In conclusion, FRT cells forced to express Cx32 give rise to domes that transform into closed inside-out follicles. This gain of function appears Cx specific, as FRT-Cx43 cells did not form similar structures. Our data suggest that the formation and/or functioning of Cx32 gap junctions might represent a key event in thyroid epithelium morphogenesis, i.e. formation of a lumen from a tight epithelial cell layer.
Animals↗
Hormonal regulation of radioiodide uptake activity and Na+/I- symporter expression in mammary glands.
The observation that radioiodide uptake (RAIU) activity, mediated by the Na+/I- symporter (NIS), is significantly increased in lactating breast suggests that RAIU and NIS expression in mammary gland are modulated by hormones involved in active lactation. We showed that both the NIS expression level and RAIU in rat mammary gland are maximal during active lactation compared to those in the mammary glands of virgin and pregnant rats as well as the involuting mammary gland. In the lactating mammary gland, NIS is clustered on the basolateral membrane of alveolar cells as a lesser glycosylated form than NIS in thyroid. The RAIU of lactating mammary gland was partially inhibited by treatment with a selective oxytocin antagonist or bromocriptine, an inhibitor of PRL release. These findings suggest that RAIU and NIS expression in mammary gland are at least in part modulated by oxytocin and PRL. Indeed, we showed that NIS messenger ribonucleic acid level was increased in a dose-dependent manner by oxytocin and PRL in histocultured human breast tumors.
Animals↗
Different functions for the thyroid hormone receptors TRalpha and TRbeta in the control of thyroid hormone production and post-natal development.
The biological activities of thyroid hormones are thought to be mediated by receptors generated by the TRalpha and TRbeta loci. The existence of several receptor isoforms suggests that different functions are mediated by specific isoforms and raises the possibility of functional redundancies. We have inactivated both TRalpha and TRbeta genes by homologous recombination in the mouse and compared the phenotypes of wild-type, and single and double mutant mice. We show by this method that the TRbeta receptors are the most potent regulators of the production of thyroid stimulating hormone (TSH). However, in the absence of TRbeta, the products of the TRalpha gene can fulfill this function as, in the absence of any receptors, TSH and thyroid hormone concentrations reach very high levels. We also show that TRbeta, in contrast to TRalpha, is dispensable for the normal development of bone and intestine. In bone, the disruption of both TRalpha and TRbeta genes does not modify the maturation delay observed in TRalpha -/- mice. In the ileum, the absence of any receptor results in a much more severe impairment than that observed in TRalpha -/- animals. We conclude that each of the two families of proteins mediate specific functions of triiodothyronin (T3), and that redundancy is only partial and concerns a limited number of functions.
Animals↗
Effectiveness of a manual disinfection procedure in eliminating hepatitis C virus from experimentally contaminated endoscopes.
BACKGROUND: Transmission of hepatitis C virus (HCV) through endoscopy has been reported, but the implications as a public health concern remain controversial. This study investigated the degree to which a thorough manual cleaning-washing-disinfection procedure can decontaminate all channels of a flexible submersible endoscope experimentally contaminated with HCV. METHODS: To assess the accuracy of the method currently in use, the initial investigation focused on sampling effectiveness. Nine endoscopes were contaminated with high-titer HCV-positive plasma and flushed with 150 mL of sampling solution (distilled water) before disinfection. To assess the effectiveness of the disinfection procedure, the following sequence was performed on another 10 endoscopes: inoculation, disinfection, and sampling. After concentration residual viruses were detected by means of RNA amplification with commercial assays. RESULTS: The study showed that sampling alone can reduce viral titer to one-fourth its original value. Within the limits of this method, HCV RNA was never detected by means of polymerase chain reaction after disinfection, whereas all internal amplification controls were positive. This reduction to less than 1/100,000 of original titer exceeds the criterion expected for the virucidal activity of disinfectants. CONCLUSIONS: The results of this in vitro experiment provided evidence that patient-to-patient endoscopic transmission HCV can be reduced, if not eliminated, with the current mechanical cleaning-washing-disinfection procedure.
Disinfectants↗
Differential actions of the dopamine agonist bromocriptine on growth of SMtTW tumors exhibiting a prolactin and/or a somatotroph cell phenotype: relation to dopamine D2 receptor expression.
Dopamine (Da) and Da agonists are known to inhibit secretion and proliferation of normal and tumoral PRL cells, through receptors of D2 subtype. Because of the lack of an experimental model, the relationship between bromocriptine (BR) sensitivity and D2 receptor expression is poorly documented. Such a relationship was analyzed using five lineages of spontaneous transplantable rat pituitary tumors (SMtTW) exhibiting different PRL/GH phenotypes. From plasma PRL and GH concentrations of rats bearing the tumors and tumor messenger RNA contents, tumors were classified as PRL (SMtTW2), somatotroph (SMtTW10), or somatomammotroph (SMtTW5) tumors. Two lineages (SMtTW3 and SMtTW4) represented variants producing PRL and GH but with a high predominance of PRL. With the exception of SMtTW4 tumors, which were malignant, all the tumors were benign and differed in their growth rate. Hormone production and growth of tumors with a PRL or a somatomammotroph phenotype were reduced by about 90% under BR treatment, whereas somatotroph tumors and the PRL malignant tumors were totally insensitive to BR. D2 receptor messenger RNA was present in all BR-sensitive tumors and was not detected in BR-resistant tumors. In conclusion, using five lineages of SMtTW tumors that are representative of the most frequent tumors encountered in human pituitary pathology, we found a full concordance between tumor responses to BR and the expression of D2 receptor by the tumors. The identification of a tumor lineage with a malignant phenotype, secreting high amounts of PRL and presenting a resistance to BR, supports the idea that Da-resistant prolactinomas are aggressive tumors.
Animals↗
Regulation of the three-dimensional organization of thyroid epithelial cells into follicle structures by the matricellular protein, thrombospondin-1.
Thyroid epithelial cells in primary culture have the capacity to organize into thyroid-specific three-dimensional structures, the follicles, in response to TSH. We studied whether thrombospondin 1 (TSP1), which represents, besides thyroglobulin, the main protein secreted by thyroid cells, could play a role in the process of folliculogenesis. TSH promoted follicle formation and inhibited TSP1 production. On the contrary, the phorbol ester, 12-O-tetradecanoyl-phorbol 13-acetate (1-100 nM) prevented TSH-induced follicle formation and strongly increased the synthesis of TSP1. Activation of TSP1 synthesis was dependent upon messenger RNA synthesis. Transforming growth factor-beta, like 12-O-tetradecanoyl-phorbol 13-acetate, increased TSP1 synthesis and prevented TSH-induced follicle formation. Thus, signaling molecules that depressed or conversely activated TSP1 production, respectively promoted or prevented thyroid folliculogenesis. TSP1, purified from platelets, was devoid of effect on cell substratum attachment, but exerted a concentration-dependent inhibition of the TSH-activated reconstitution of thyroid follicles (half-inhibition at 40 microg/ml). TSP1 exhibited the same effect when added to thyroid cell aggregates representing primitive follicle structures. Our data suggest that the control of thyroid follicle formation may operate at least in part through regulation of the production of the matricellular protein TSP1, which acts as a negative modulator of the cell-cell adhesion process involved in thyroid follicle morphogenesis.
Animals↗
Susceptibility of differentiated thyrocytes in primary culture to undergo apoptosis after exposure to hydrogen peroxide: relation with the level of expression of apoptosis regulatory proteins, Bcl-2 and Bax.
Thyrocytes, that generate and use hydrogen peroxide (H2O2) to synthesize thyroid hormones, undergo apoptosis, as do most cell types, when exposed in vitro to H2O2. We have studied 1) the kinetics and the amplitude of the apoptotic response to H2O2 and 2) the relationship between the extent of the apoptosis-inducing effect of H2O2, the H2O2 degradation activity, and the level of expression of apoptosis regulatory proteins, Bcl-2 and Bax, in pig thyrocytes in primary culture. Cells were seeded at high density to obtain confluent monolayers and were cultured in the presence of TSH to maintain the expression of differentiation. H2O2 (10-300 microM) induced the appearance of cells with fragmented DNA (terminal transferase deoxy-UTP-fluorescein isothiocyanate nick end labeling-positive cells) at a maximum of 3-4 h after H2O2 addition and then the detachment of apoptotic cells from the cell monolayer. The proportion of detached cells increased with H2O2 concentration and amounted to up to 30% of the initial cell number after 24 h. The transient effect of H2O2 was related to its rapid degradation by cells and culture medium components (rate constant, approximately 0.1 min(-1)). Iterative additions of H2O2 produced cumulative apoptotic waves. The amplitude of the apoptotic response of thyrocytes to H2O2 progressively increased with the time of culture, up to 4-fold from days 1-8. This was not related to a change in the capacity of thyrocytes to degrade H2O2. During the same period of culture, the Bcl-2 cell content progressively decreased, whereas that of Bax concomitantly increased; thus, the Bcl-2/Bax ratio varied from about 6 on day 1 to 0.5 on day 10. These data show that the susceptibility of thyrocytes to undergo apoptosis increases with the time of culture and that the pronounced changes in the apoptotic status ofthyrocytes might be linked to coordinate modifications of the level of expression of pro- and antiapoptotic regulatory proteins.
Animals↗
Identification of thyroid hormone residues on serum thyroglobulin: a clue to the source of circulating thyroglobulin in thyroid diseases.
Thyroglobulin (Tg) present in the serum of normal individuals and patients with thyroid disorders could be partly newly synthesized non-iodinated Tg and partly Tg containing iodine and hormone residues originating from the lumen of thyroid follicles. With the aim of examining the contribution of the latter source of Tg to the elevation of serum Tg concentration in thyroid pathophysiological situations, we devised a procedure to identify thyroxine (T4) and tri-iodothyronine (T3) residues on Tg from unfractionated serum. A two-step method, basedon (i)adsorption of Tg on an immobilized anti-human Tg (hTg) monoclonal antibody (mAb) and (ii)recognition of hormone residues on adsorbed Tg by binding of radioiodinated anti-T4 mAb and anti-T3 mAb, was used to analyze serum Tg from patients with either Graves' disease (GD), subacute thyroiditis (ST) or metastatic differentiated thyroid cancer (DTC). Purified hTg preparations with different iodine and hormone contents were used as reference. Adsorption of purified Tg and serum Tg on immobilized anti-hTg mAb ranged between 85 and 90% over a wide concentration range. Labeled anti-T4 and anti-T3 mAbs bound to adsorbed purified Tg in amounts related to its iodine content. Tg adsorbed from six out of six sera from ST exhibited anti-T4 and anti-T3 mAb binding activities. In contrast, significant mAb binding was only observed in one out of eight sera from untreated GD patients and in 1 out of 13 sera from patients with DTC. The patient with DTC, whose serum Tg contained T4 and T3, represented a case of hyperthyroidism caused by a metastatic follicular carcinoma. In conclusion, we have identified, for the first time, T4 and T3 residues on circulating Tg. The presence of Tg with hormone residues in serum is occasional in GD and DTC but is a common and probably distinctive feature of ST.
Antibodies, Monoclonal↗
Expression of alpha- and beta-subunits and activity of Na+K+ ATPase in pig thyroid cells in primary culture: modulation by thyrotropin and thyroid hormones.
Na+ K+ ATPase located at the basolateral pole of thyroid epithelial cells, contributes to thyroid hormone synthesis by generating the driving force for the uptake of the substrate, iodide. We have investigated whether the expression of the alpha- and beta-subunits and activity of Na+ K+ ATPase were subjected to variations in response, (a) to TSH, that controls the expression of differentiation in thyroid cells and (b) to thyroid hormones as potential autocrine factors. Studies were carried out on pig thyroid cells cultured (a) without TSH to obtain thyroid cell monolayers (TCM) in basal state or (b) with TSH in the form of cell monolayers (TCM-T) or as reconstituted thyroid follicles (RTF). Iodide uptake activity, thyroperoxidase protein and thyroglobulin mRNA taken as parameters of thyroid cell differentiation were 6 to 25-fold higher in RTF and TCM-T than in TCM. Western blot analyses of Na+ K+ ATPase subunits revealed that the alpha-subunit (105 kDa) content of TCM-T and RTF was similar but 8-fold higher than that of TCM. In contrast, the beta-subunit (50 kDa) content of TCM-T and RTF was only about twice that of TCM. Similar relative variations were observed at the mRNA level for both alpha- and beta-subunits. Na+ K+ ATPase activity was only 40% higher in RTF and TCM-T than in TCM. A 48 h treatment of RTF by either T4 or T3 (1-100 nM) induced a 3-fold increase of the alpha-subunit but did neither alter the beta-subunit nor the Na+ K+ ATPase activity. In conclusion, Na+ K+ ATPase activity and the level of expression of its beta-subunit, known to control the assembly and targetting of alpha-beta oligomers and thus the amount of functional sodium pump at the plasma membrane, are only moderately altered when thyroid cells undergo major changes in their differentiation status. Our data show that the expression of the alpha-subunit of Na+ K+ ATPase by thyroid cells is up-regulated by TSH and thyroid hormones.
Animals↗
Analyses of the molecular forms of serum thyroglobulin from patients with Graves' disease, subacute thyroiditis or differentiated thyroid cancer by velocity sedimentation on sucrose gradient and Western blot.
Serum thyroglobulin (Tg) concentration increases in diverse thyroid pathophysiological situations. We examined whether Tg molecules appearing in the serum of patients with Graves' disease (GD), subacute thyroiditis (ST) or differentiated thyroid cancer (DTC) have distinctive biochemical properties. We used ultracentrifugation on sucrose gradient and Western blot to analyze structural parameters of immunoreactive Tg in complete serum from 40 patients with GD, ST or DTC. Purified human Tg was used as reference. Immunoreactive Tg from ST or DTC sera sedimented in a single, rather symmetrical peak as purified 19S Tg. In GD sera without detectable anti-Tg autoantibodies (TgaAb), about 80% of immunoreactive Tg was recovered in a Tg dimer peak that often split into two components; the remaining Tg immunoreactivity (10-30%) sedimented faster and was polydispersed. In GD sera containing TgaAb, immunoreactive Tg was recovered in a peak sedimenting faster than 19S Tg corresponding to immune complexes identified by protein A adsorption. Using a Western blot procedure, optimized to detect 0.1 ng Tg in serum. a single band of Tg, migrating as the intact Tg subunit, was always found in non-reducing conditions; the intensity of the band correlated with the immunoassayable Tg concentration. In reducing conditions, the Tg band obtained with GD or ST sera was decreased by up to 70% compared with that of purified Tg or serum Tg from patients with DTC. In conclusion, serum Tg from DTC is remarkably homogeneous and in the form of dimers dissociable into uncleaved monomers. In contrast, serum Tg from GD or ST is heterogeneous with respect to its sedimentation properties and/or the structural integrity of its polypeptide chains. These data provide information on the processes whereby Tg is released into the circulation.
Antibodies↗
H2O2 induces apoptosis of pig thyrocytes in culture.
Apoptosis might be involved in the reduction of the thyroid cell population in physiopathological situations such as goitre involution and autoimmune deleterious processes. Up to now, little attention has been paid to the apoptotic phenomenon in the normal thyroid gland the specialized metabolism of which is expected to generate reactive oxygen species. Indeed, thyroid cells have the capacity to synthesize H2O2. In this study, we have analyzed the capacity of H2O2 to trigger apoptosis of pig thyrocytes in culture to try to determine whether thyrocytes exhibit a particular resistance to apoptosis induced by an oxidative stress. We show that exposure of thyrocytes cultured as monolayers to exogenous H2O2 induced cell death with characteristics of apoptosis. The effect of H2O2 was concentration-dependent; apoptotic cells were already observed after exposure to 50 micro M H2O2. At high concentrations (millimolar range), H2O2 exerted toxic effects leading to rapid cell disruption. Within the first hour after the onset of exposure to 50-300 micro M H2O2, early signs of apoptosis, i.e. DNA fragmentation, appeared in a low (0.1-1%) but definite fraction of thyrocytes. The proportion of adherent cells exhibiting DNA fragmentation remained fairly constant after 6, 15 and 24 h. During the 24-h period, an increasing number of cells detached from the culture dish and up to 30-40% of cells in suspension displayed apoptotic features. The fraction of cells that lost contact with the culture dish amounted to up to 25% 24 h after addition of 300 micro M H2O2. In conclusion, as reported for other cell types, low H2O2 concentrations are capable of triggering apoptosis in thyrocytes cultured as monolayers. Thyrocytes that undergo apoptosis secondarily lose contact with neighbour cells and the substratum; cell detachment from the monolayer probably happens within 1-2 h after initiation of DNA fragmentation. Our data show that the apoptotic commitment can take place many hours after initiation of the oxidative stress.
Animals↗
Restoration of cell-to-cell communication in thyroid cell lines by transfection with and stable expression of the connexin-32 gene. Impact on cell proliferation and tissue-specific gene expression.
Normal thyroid epithelial cells coexpress connexin-32 and connexin-43, which form distinct gap junctions. In primary culture, connexin-43 is expressed by thyrocytes in monolayers or reorganized into follicles, whereas the expression of connexin-32 is dependent upon the reconstitution of follicles. To study the functional impact of connexin-32 gap junctions in thyroid cells, we transfected connexin-32 cDNA in two thyroid-derived communication-deficient cell lines, FRT and FRTL-5. The selected clones, which stably expressed connexin-32 at high levels and exhibited high gap junction-mediated dye-coupling, presented a reduced proliferation rate as compared with that of the corresponding wild-type FRT and FRTL-5 cells; the mean population doubling time was increased by approximately 35%. The proliferation of connexin-32-transfected FRTL-5 cells remained thyrotropin-dependent; the range of thyrotropin concentrations that stimulated growth was the same in transfected and control cells. The expression of connexin-32 led to an increase of thyroglobulin gene expression in FRTL-5 cells. The expression of two other tissue-specific proteins, thyroid transcription factor-1 and Pax-8, was unchanged. These findings provide evidence that connexin-32 gap junction-mediated cell-to-cell communication participates in the control of growth and differentiation of thyroid cells.
Animals↗