Cultured Porcine Thyroid Cells Research Articles

SUN-LB129 Thyroglobulin Stimulates the Secretion of Thyroxine From Thyroid Epithelial Cells in Suspension Culture via Nuclear Factor-κB Signaling Pathway

The nuclear factor (NF)-κB signaling pathway controls a variety of biological functions such as cell growth and differentiation as well as immune and inflammatory responses. Two distinct pathways of NF-κB activation are known. NF-κB signaling via non-canonical pathway plays an important role in maintaining normal thyroid function, namely, thyroid cells survival and expression of thyroid-specific proteins, such as NIS, TPO and thyroglobulin (Tg). The primary function of thyroid cells is the production of thyroid hormones, which are cleaved out by various processing enzymes from the modified tyrosine residues of the Tg molecule. Although Tg is currently recognized as no more than a scaffold protein for thyroid hormone synthesis, our group has shown that Tg stimulates the proliferation of rat thyroid follicular FRTL-5 cells via PI3K pathway. The signaling pathways underlying various functions of thyroid cells have been extensively investigated but some discrepancies still exist, depending on the experimental model systems and the types of cells used. Recently, our group discovered that Tg may directly regulate the synthesis of thyroid hormones in thyroid cells. In this study, we performed suspension culture of porcine thyroid cells and aimed to elucidate the mechanism of the effect of Tg on thyroid cells. Porcine thyroid epithelial cells were prepared from thyroid gland by enzymatic digestion and cultured in monolayer or in suspension culture. Various concentrations of Tg were added to the medium and cultured for several days. Then, the conditioned medium was collected and the amount of thyroid hormone was measured by reversed phase chromatography; the cells were harvested and mRNA levels of hormone-processing enzymes, cathepsin B, K, L and dipeptidyl peptidase I, II (DPP I, II), were measured by quantitative PCR. The amount and activation of cell signaling molecules were also evaluated by western blotting. Tg stimulated the secretion of thyroid hormone, thyroxine, from porcine thyroid cells in suspension culture, however, no stimulation by Tg was observed in monolayer culture. The expression of mRNAs of cathepsin B, K and L were reduced and that of DPP II was increased by the treatment of Tg in suspension culture. Tg increased the amount of NF-κB p52 and Rel B dose dependently. On the other hand, TSH had little effects on the amount of these proteins. Tg and TSH both activated PDK1 and MAPK p44/42 but not Akt. These results suggest that Tg regulates thyroid hormone synthesis in totally different way from TSH by altering the expression levels of hormone-processing enzymes in thyroid cells. This stimulatory effect might be mediated by NF-κB signaling pathway, whereas the proliferative effect of Tg under these conditions might be exerted via MAPK signaling pathway. The detailed mechanisms of these effects of Tg on thyroid cells are under investigation.

Prostacyclinと甲状腺: 甲状腺細胞培養下で, 培地に加えたTSHはPGI2を選択的に増加させ, そのPGI2はcAMPを増加させ, ヨード代謝を充進させる

Prostacyclinと甲状腺: 甲状腺細胞培養下で, 培地に加えたTSHはPGI2を選択的に増加させ, そのPGI2はcAMPを増加させ, ヨード代謝を充進させる

Significance of thyroglobulin antibodies cross-reactive with thyroperoxidase (TGPO antibodies) in individual patients and immunized mice.

Thyroglobulin (TG) and thyroperoxidase (TPO), both involved in thyroid hormone synthesis, represent major autoantigens in thyroid autoimmune disease. Despite numerous studies, the emergence, pathophysiological significance and role of autoantibodies to TG and TPO remain elusive. The recent identification of a new category of thyroid-specific autoantibody interacting with both TG and TPO (TGPO autoantibodies) offers a new opportunity in the study of thyroid autoimmunity. To gain a better insight into the significance of these TGPO autoantibodies, measurement in individual samples appeared necessary. The unique property of TGPO autoantibodies, simultaneous binding to TG and TPO, was used to set up a sandwich method which combined coated TG and radio-iodinated TPO. This method was found to be strictly specific for TGPO autoantibodies and sensitive enough to assay TGPO autoantibodies in serum. In humans, TGPO autoantibodies were found in most of the sera with high TG and TPO autoantibody titres, but not in sera negative for TG autoantibodies, whatever the TPO autoantibody titre. Furthermore, high TGPO autoantibody titres were found in sera strongly cytotoxic for cultured porcine thyroid cells. However, significant correlation of TGPO autoantibody titre was observed neither with TG and TPO autoantibody titres (n = 48) nor with complement-dependent cytotoxicity (n = 50). TGPO antibody assay was also performed in individual plasma of CBA/J mice immunized with either human TG (n = 6) or human TPO (n = 6). Immunization with TG induced high levels of not only TG but also TGPO antibodies, which exhibited a strong reactivity for TPO and whose binding to TG and TPO was fully inhibited by TG. In contrast, immunization with TPO induced high levels of only specific TPO antibodies accompanied by low levels of specific TG antibodies. In this case TGPO antibodies were not detected. Of note, TG- and TPO-immunized mice mounted an immune response against their own TG, but did not exhibit histological signs of thyroiditis. Large panels of TG and TPO MoAbs were also investigated with this method: 18/25 TG MoAbs and only 1/13 TPO MoAbs were found cross-reactive. Taken together, these data provide evidence that TGPO antibodies are effectively present in individual patients and TG-immunized mice, are different from specific TG and TPO antibodies, and may derive from natural B cell repertoire by autoimmune processes involving TG and not TPO.

Hexamethylene bisacetamide (HMBA) increases thyroglobulin levels in porcine thyroid cells without increasing cyclic-AMP.

The polar planar compound hexamethylene bisacetamide (HMBA) is an inducer of terminal differentiation which has been extensively studied in the murine erythroleukemia cells (MELC). We have tested this compound in normal porcine thyroid cells in primary culture where it either activates or inhibits the major tissue specific functions of these cells: it induces the reorganization of cells into follicles, prevents the loss of thyrotropin sensitivity in monolayer cells, activates cell growth but inhibits their iodide metabolism. In this paper, we demonstrate that HMBA acts on the total thyroglobulin levels measured in cell layers plus media. This specific marker of thyroid tissue is increased by HMBA both in kinetics and in concentration-response experiments. HMBA per se does not increase the total cyclic AMP measured either during the first hours after stimulation or in the following days when compared to controls. As expected, cyclic AMP in the same experiment increased rapidly within minutes after the cells were challenged by TSH (positive control). Altogether, the results show that the drug HMBA mimics thyrotropin effects on thyroglobulin levels measured in porcine thyroid cells in culture. This modulation cannot be explained by an increase in cyclic AMP, indicating that despite similarities between TSH and HMBA effects, the mechanism of the mode of action of these two molecules is very different.

DIDS (4,4′-diisothiocyanatostilbene-2,2′-disulfonic acid) increases iodide trapping, inhibits thyroperoxidase and antagonizes the TSH-induced apical iodide efflux in porcine thyroid cells

4,4′-Di-isothiocyanatostilbene-2,2′-disulfonic acid (DIDS), an inhibitor of several anionic channels and transporters including the band 3 protein of the red blood cell membrane was tested on iodide metabolism in cultured porcine thyroid cells. We used three experimental cell culture models: (i) forskolin-stimulated correctly inside-in polarized follicle-associated thyroid cells cultured onto plastic support (ii) suspensions of isolated cells derived from such cultures (iii) polarized monolayers in bicameral chambers. DIDS was observed to increase free-iodide trapping in all conditions. Organification of iodide by follicle-associated cell cultures incubated for 6 h decreased as a function of DIDS concentration with an IC 50 of 5×10 −5 M. This block in organification is accounted for a block in thyroperoxidase activity as in vitro both purified lactoperoxidase and purified porcine thyroperoxidase were inhibited by DIDS with a similar dose-dependency the IC 50 being also of 5×10 −5 M. Both control and DIDS-treated cells in suspension, actively trapped iodide and reached a steady concentration in about 50 min; however the plateau was 4.4-fold higher in (10 −3 M) DIDS-treated cells. Acute TSH-stimulation at this plateau of 125I-preloaded cells in suspension in the presence of 2 mM methimazole (MMI) induced a fast release of iodide from these cells as expected (first step of the TSH-biphasic effect). This TSH-induced iodide efflux was however completely inhibited by DIDS (10 −3 M). Furthermore, addition of DIDS to the apical compartment of TSH-prestimulated cell monolayers in bicameral chambers resulted in an increase in intracellular-iodide concentration and in an inhibition of iodide efflux into the apical medium. Taken together, the present results demonstrate that DIDS mainly interacts with two main components of the thyroid apical cell membrane: thyroperoxidase and a cAMP-sensitive iodide channel.

Protein tyrosine phosphorylation influences adhesive junction assembly and follicular organization of cultured thyroid epithelial cells.

The follicular histoarchitecture of the thyroid forms the anatomical basis for thyroid physiology and is commonly disturbed in diseases of the thyroid. We have used cultured porcine thyroid cells to study thyroid epithelial morphogenesis and its regulation. When cultured in the presence of TSH, freshly isolated thyroid cells reorganize to form follicles within three-dimensional cell aggregates. However, when established follicles are washed into TSH-free medium, thyroid cells spread and migrate to convert follicles into confluent epithelioid monolayers, activating morphogenetic mechanisms, such as cell locomotility, that may be relevant to thyroid inflammation and tumor invasiveness. The phenomenon of follicle to monolayer conversion, therefore, provides an opportunity to identify morphogenetic mechanisms that 1) must be tonically inhibited to maintain follicular organization and 2) may contribute to pathogenetic disturbances of follicular architecture when functioning aberrantly. In this study we found that follicle to monolayer conversion is associated with an increase in cellular phosphotyrosine. This was particularly evident at nascent focal adhesions (cell-substrate adhesive junctions) and later at cell-cell junctions. Focal adhesion assembly was accompanied by reorganization of the actin cytoskeleton, with the appearance of prominent stress fibers. Genistein, a potent inhibitor of protein tyrosine kinases, inhibited the accumulation of phosphotyrosine, focal adhesion assembly, and follicle to monolayer conversion. We conclude that tyrosine phosphorylation exerts an important influence on thyroid epithelial organization in culture, at least partly mediated through regulation of focal adhesion assembly.

Oncostatin M: a new potent inhibitor of iodine metabolism inhibits thyroid peroxidase gene expression but not DNA synthesis in porcine thyroid cells in culture.

The functions of thyroid cells are regulated by a number of cytokines and growth factors in addition to TSH. Recent studies have revealed that several cytokines including interleukin (IL)-6 are involved in thyroid dysfunction. Oncostatin M (OSM) is a glycoprotein belonging to the same family of cytokines as IL-6, to which it is related by sequence and structural homology and the use of the signal-transducing receptor component gp130. We, therefore, studied the effect of OSM on iodide uptake and DNA synthesis by porcine thyroid cells in culture. OSM increased c-fos and c-jun mRNA levels but did not stimulate DNA synthesis. OSM inhibited iodide uptake stimulated by TSH; while IL-6 also inhibited iodide uptake, it was only about one-tenth as potent. IL-6 had about the same potency as OSM when it was added with soluble IL-6 receptor. OSM had no effect on cAMP production but inhibited iodide uptake stimulated by 8-bromo-cAMP and forskolin. These findings suggest that OSM exerts its inhibitory effects at the post-cAMP production step(s). OSM also inhibited thyroid peroxidase mRNA levels but had little effect on thyroglobulin mRNA levels. Investigations of the signal transduction system showed that gp130 and leukemia inhibitory factor (LIF) receptor beta subunit mRNA were detectable in porcine thyroid cells by reverse transcription (RT)-polymerase chain reaction (PCR). Together with the report that serum OSM and IL-6 concentrations are elevated to the same levels in patients with sepsis, these results suggest that OSM may contribute to the thyroid dysfunction in this condition.

Effects of bile acids on iodide uptake and deoxyribonucleic acid synthesis in porcine thyroid cells in primary culture.

The effects of bile acids on iodide uptake and DNA synthesis were studied in cultured porcine thyroid cells. All five bile acids, which are commonly found in serum, chenodeoxycholic acid (CDCA), cholic acid (CA), deoxycholic acid (DCA), lithocholic acid (LCA), and ursodeoxycholic acid (UDCA) dose-dependently inhibited both basal and TSH-induced iodide uptake at concentrations of 25-250 microM. Since CDCA is one of the two major primary endogenous bile acids, were studied mainly the effects of CDCA. The inhibitory effect of CDCA was detected after 24 h treatment of thyroid cells, and was dependent on the time of exposure up to 72 h. Treatment of thyroid cells with CDCA for 72 h inhibited cAMP production stimulated by 50 mU/L TSH or 0.5 mg/L forskolin and also inhibited iodide uptake induced by 0.5 mM 8-bromo cAMP or 0.5 mg/L forskolin. These results suggest that CDCA inhibits iodide uptake by decreasing cAMP production as well as post-cAMP generation. Bile acids except LCA stimulated [3H]thymidine incorporation into the thyroid cells by itself, indicating that the inhibitory effect of bile acids on iodide uptake is not due to cytotoxic effect. In conclusion, these findings suggest that the direct inhibition of thyroid function by bile acids might cause hypothyroidism in chronic liver disease.

Evidence for a TSH-Controlled Ectophosphotyrosine Phosphatase in Pig Thyroid Cultured Cells

In porcine thyroid cells in primary culture, thyrotropin (TSH) provokes important morphological changes associated with specific thyroidal function recovery. TSH influences cell–cell interactions and follicular morphogenesis. In the present report, we identify an ectotyrosine phosphatase activity controlled by chronic treatment with TSH. Specific substrates and various inhibitors allowed us to characterize this activity. This tyrosine phosphatase is located at the outer surface of thyroid cells as demonstrated by phosphotyrosylhistone hydrolysis. Control of cell viability and trypsin treatment confirm this extracellular localization. These data show that TSH activates ectotyrosine phosphatase activity, suggesting a role for surface protein phosphorylation in regulating specific functions of porcine thyroid cells in suspension.

Effects of activin A on deoxyribonucleic acid synthesis, iodine metabolism, and cyclic adenosine monophosphate accumulation in porcine thyroid cells.

We have recently shown the presence of activin A in human thyroid cells. To determine whether activin A affects the growth and function of the thyroid, we investigated its effects on DNA synthesis, iodine metabolism, and cAMP accumulation in cultured porcine thyroid cells. Activin A increased DNA synthesis. This effect was abolished by addition of follistatin but additively enhanced by epidermal growth factor. In contrast, activin A significantly reduced uptake and release of iodide by the thyroid and also TSH-induced cAMP accumulation but did not inhibit the cAMP accumulation induced by forskolin. These data indicate that activin A stimulates thyroid growth irrespective of cAMP accumulation and inhibits thyroid function.

Effects of transforming growth factor α (TGF-α) on DNA synthesis and thyrotropin-induced iodine metabolism in cultured porcine thyroid cells

Transforming growth factor alpha (TGF-alpha) is a potent mitogen that is similar structurally to epidermal growth factor (EGF). As EGF is a potent growth stimulator and an inhibitor of iodine metabolism in cultured thyroid cells of several species, we studied whether TGF-alpha has similar effects using porcine thyroid cells in culture. Recombinant human TGF-alpha dose-dependently stimulated DNA synthesis of thyroid cells, with maximal stimulation (eight- to ninefold above basal) occurring at 2 nmol/l. The potency was approximately 50% that of mouse EGF and correlated with the ability to compete with EGF for receptor binding, suggesting that the action of TGF-alpha is mediated by interaction with EGF receptors. When thyroid cells were cultured for 3 days with thyrotropin (TSH) in the presence of TGF-alpha, TSH-induced iodide uptake was inhibited in a dose-dependent manner. The potency of TGF-alpha again was approximately 50% that of EGF. Transforming growth factor alpha did not inhibit TSH-stimulated cAMP production. Moreover, iodide uptake stimulated by either forskolin or 8-bromo-cAMP also was inhibited by TGF-alpha. Thus, we conclude that TGF-alpha inhibits TSH-induced iodine metabolism largely by acting at the steps distal to cAMP production. Northern blot analysis revealed expression of TGF-alpha mRNA in porcine thyroid cells. These observations suggest that TGF-alpha acts as an autocrine modulator of growth and differentiated functions in porcine thyroid cells.

Chloride Channel Blockers Inhibit the Na+/I− Symporter in Thyroid Follicles in Culture

Porcine thyroid cells in culture are able to reorganize into well-polarized follicle-like structures in the presence of cAMP analogs. These follicles exhibit on their basolateral membrane domain the Na+/I− symporter which allows iodide to accumulate in the thyrocytes. The initial rate of iodide influx through the Na+/I− symporter is inhibited up to 98% by the chloride channel blockers. 5 nitro-2(3-phenylpropylamino)benzoic acid and 3′,5-Dichlorodiphenylamine-2-carboxylic acid are the most effective inhibitors, with a K0.5 value of 60 μM. This inhibition is not secondary to inhibition of chloride transport. Other chloride transporter blockers have been studied but showed lesser activities.

The effects of hydrocortisone and RU486 (mifepristone) on iodide uptake in porcine thyroid cells in primary culture.

The effects of hydrocortisone on iodide uptake and DNA synthesis were studied in porcine thyroid cells cultured in phenol red-free medium supplemented with low concentrations (0-1%) of charcoal-stripped fetal calf serum. Hydrocortisone dose-dependently stimulated TSH-induced iodide uptake at physiological concentrations (1-1000 nM), and the minimum detectable dose was 33 nM hydrocortisone. Treatment of thyroid cells with hydrocortisone for 72 h increased cAMP production stimulated by TSH. In addition, this stimulatory effect of hydrocortisone was observed when iodide uptake was induced with 0.25 mM 8-bromo-cAMP. These results suggest that hydrocortisone stimulates iodide uptake, influencing cAMP production and post-cAMP pathways. The synthetic glucocorticoid antagonist RU486 alone had no effect on iodide uptake in porcine thyroid cells; however, along with TSH, RU486 a weak agonist activity. As a glucocorticoid antagonist, RU486 inhibited the stimulatory actions of hydrocortisone on iodide uptake in combination with TSH and also with 8-bromo-cAMP, suggesting a specific effect of hydrocortisone mediated by a glucocorticoid receptor. The effect of hydrocortisone on thyroid cell multiplication was also studied. Hydrocortisone decreased [3H]thymidine incorporation into DNA slightly but not significantly when the cells were treated with 100 ng/ml insulin-like growth factor-I and hydrocortisone. In summary, it has been demonstrated that hydrocortisone directly stimulated the function of porcine thyroid cells at physiological concentrations, by using a glucocorticoid receptor and by affecting cAMP pathways. The data that RU486 inhibited iodide uptake induced by hydrocortisone and TSH propose that monitoring of thyroid function may be necessary if RU486 is been used for a long time.

The effects of hydrocortisone and RU486 (mifepristone) on iodide uptake in porcine thyroid cells in primary culture

The effects of hydrocortisone and RU486 (mifepristone) on iodide uptake in porcine thyroid cells in primary culture

Interaction of endothelin-1 with porcine thyroid cells in culture: a possible autocrine factor regulating iodine metabolism.

Although endothelins were originally discovered as peptides with vasoconstrictor activity, recent studies have indicated a number of endothelin (ET)-induced hormonal functions in various tissues. We have studied the interaction of endothelins with porcine thyroid cells in culture. Specific binding of 125I-labelled ET-1 was demonstrated in porcine thyroid cells. The binding was displaced equally by unlabelled ET-1 and ET-2, but receptor affinity for ET-3 was lower than that for ET-1 and -2. Scatchard analysis of the data revealed a single class of high-affinity ET-1 receptors with a Kd of 0.45 nmol/l and a binding capacity of 2100 sites/cell. SDS-PAGE and autoradiography of 125I-labelled ET-1 cross-linked with thyroid cell membranes demonstrated ET-1 binding sites with an apparent molecular weight of 50 kDa. These results indicated that ET-1 receptors in thyroid cells are type A ET receptors. In association with the presence of ET-1 receptors, porcine thyroid cells responded to ET-1 and ET-2 with an increase in c-fos mRNA expression. Although ET-1 did not affect DNA synthesis stimulated by either EGF or IGF-I, it dose-dependently inhibited TSH-induced iodide uptake and also inhibited iodide uptake stimulated by forskolin and 8-bromo-cAMP. ET-1 had no effect on TSH-stimulated cAMP production. Thus, ET-1 inhibited TSH-induced iodine metabolism by acting at the steps distal to cAMP production. In agreement with a recent report, immunoreactive ET-1 was detected in medium conditioned by porcine thyroid cells. Antibody to ET-1 was found to increase TSH-induced iodide uptake.(ABSTRACT TRUNCATED AT 250 WORDS)

Differential expression of thrombospondin, collagen, and thyroglobulin by thyroid‐stimulating hormone and tumor‐promoting phorbol ester in cultured porcine thyroid cells

In the present study, we have investigated the potential regulation of thyroglobulin (Tg) and extracellular matrix components synthesis by thyroid-stimulating hormone (TSH) and tetradecanoyl phorbol-13-acetate (TPA) on thyroid cells. Porcine thyroid cells isolated by trypsin-EGTA digestion of thyroid glands were maintained in serum containing medium on poly (L-lysine)-coated dishes. Cells differentiated into follicular or vesicular-like structures were distinguished by their ability to organify Na[125I] and to respond to TSH stimulation. After an incubation of the cells with radiolabeled proline or methionine, two major proteins were identified, p450-480 and p290 (so named because of their molecular masses). Tg (p290) synthesis was demonstrated by the synthesis of [131I]-labeled polypeptides with electrophoretic properties identical to those of authentic Tg molecules. P450-480 resolved to M(r) 190,000 under reducing sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) conditions. It was identified as thrombospondin by its reactivity with a monoclonal anti-human thrombospondin and by peptide sequencing of some of its tryptic fragments that displayed identity to thrombospondin I. Collagen synthesis was demonstrated by the formation of radioactive hydroxyproline and by the synthesis of pepsin-resistant polypeptides ranging from M(rs) 120,000 to 200,000. When the cells were cultured in the presence of 100 nM TPA, the culture medium contents of thrombospondin and collagen were increased by 2.7 and 1.6-fold, respectively, whereas Tg content was decreased by a factor 3.9. In contrast, the acute treatment of control cells with TPA induced a decrease in both Tg and collagen content by factors 3.0 and 1.5, respectively, and an increase in thrombospondin content by a factor 2.5. In the presence of 100 nM TPA, TSH (1 mU/ml) did not counteract the stimulating effect of TPA on extracellular matrix components synthesis. In contrast, when cells were cultured in the presence of TSH alone at concentrations higher than 0.1 mU/ml, collagen and thrombospondin in the medium were decreased by a factor 2.0 and 1.9, respectively, and TSH preferentially activated Tg synthesis. However, no acute response to TSH was observed in cells incubated for 2 days without effectors (control cells). On TSH differentiated cells, TPA decreased both collagen and Tg accumulation by factors 1.2 and 1.8, respectively, whereas it increased the one of thrombospondin by a factor 2. These results, together with the stimulating effect of TPA on TSH mediated cell proliferation, argue for a role of thrombospondin in cell adhesion and migration events within the thyroid epithelium.

Cyclic AMP regulation of annexins I, II, V synthesis and localization in cultured porcine thyroid cells

Porcine thyrooid cells cultured in the presence of TSH (0.1 mU/ml) or forskolin (10 −5M) for 4 days display an increased annexin I, II, V biosynthesis when compared with unstimulated cells. Annexin I mostly accumulates in the cytosolic fraction and annexins II and V in the particulate fraction. TSH and forskolin affect in the same manner annexin biosynthesis and localization. In the TSH and forskolin treated cells PGE 2 production is very low in comparison with the very high PLA 2 activity observed in the dedifferentiated control cells. A strong inhibition of the PGE 2 production is observed in control cells incubated with a purified annexin V preparation. These results suggest the existence, in porcine thyroid cells, of a cross-talk between the adenylyl cyclase system and the phospholipase A 2 mediated pathways. Annexins' biosynthesis and localization are under the control of the adenylyl cyclase system and participate in this cross-talk.

Production of thyroid stimulation blocking antibody without TSH receptor binding activity in rabbits with experimental autoimmune thyroiditis.

When rabbits were immunized with porcine thyroid plasma membrane, some cases of produced antibodies showed the blocking activity for TSH stimulated cAMP production in cultured porcine thyroid cells in spite of negative TSH binding inhibitory immunoglobulin (TBII) activity. The inhibitory effect of these thyroid stimulation blocking antibodies (TSBAbs) on cAMP increase by forskolin and GTP gamma S in porcine thyroid cells was observed in 1 and 3 rabbits, respectively. When the blocking activity of these antibodies for stimulated cAMP production by forskolin, GTP gamma S and NaF was examined in the isolated porcine thyroid membrane, no blocking activity for these 3 stimulators except in 1 case was found. The blocking activity of these antibodies could be absorbed significantly by incubation with porcine thyroid plasma membrane as antigen. The blocking activity was not observed in rabbits immunized with porcine thyroglobulin. The present experiment demonstrated that the produced antibody in rabbits against porcine thyroid membrane had the blocking activity for TSH stimulation to thyroid cells without affecting TSH binding to its receptor. These facts suggest that this type of blocking antibody may be produced against any antigen of thyroid membrane origin except the TSH receptor.

Iodine Regulation of Endothelin-1 Gene Expression in Cultured Porcine Thyroid Cells: Possible Involvement in Autoregulation of the Thyroid

We studied the regulation of endothelin (ET)-1 gene expression in porcine thyroid cells in culture. First, we demonstrated prepro-ET-1 mRNA in porcine thyroid cells. The level of the mRNA was increased by phorbol 12-myristate 13-acetate (TPA), a protein kinase C stimulator, but was decreased by TSH (1 mU/mL). However, transforming growth factor-beta and interleukin-1 beta had no effect. The amount of immunoreactive (ir)-ET-1 secreted from the cells was also increased by TPA and was decreased by TSH. Next, we studied the effect of iodide, as iodide has various effects on thyroid cells. NaI (100 microM) increased the prepro-ET-1 mRNA level. The effect of NaI was attenuated by 1 mM methimazole (MMl). The amount of ir-ET-1 released from the cells was also increased by the NaI treatment and the increase was also attenuated by MMl. These observations indicate that ET-1 gene expression is induced by organified iodine compounds in thyroid cells in a manner very similar to the inhibitory actions of iodide on thyroid cell function. The protein synthesis inhibitor, cycloheximide, superinduced prepro-ET-1 mRNA within 4 h, but NaI did not. The difference between cycloheximide and NaI suggests that the iodine effect on the gene expression is not due to nonspecific inhibition of protein synthesis. Together with our previous findings that porcine thyroid cells have ET-1 receptors and that ET-1 modulates iodine metabolism, we speculate that ET-1 produced by thyroid cells is involved in thyroid autoregulation including thyroid blood flow.

Chloride conductance of apical membrane in cultured porcine thyroid cells activated by cyclic AMP

The thyroid epithelium transports fluid bidirectionally using active transport of Na + ions from apical to basal poles and active transport of Cl - in the reverse direction. In these studies we sought evidence for cyclic AMP activated Cl - channels on the apical membranes of thyroid cells in monolayer culture. A Cl --dependent basal-positive short-circuit current (I sc) was demonstrated in bicameral chambers after blocking Na + transport with phenamil, and responded to prostaglandin (PG) E 2 with a spike of 5–10 min duration followed by a plateau. The onset of the spike coincided with an increase in the conductance of the epithelium. Application of an external Cl - concentration gradient, by replacing the medium in the apical compartment with Cl --free medium, resulted in an increase in I sc after, but not before, addition of PGE 2. Forskolin and thyroid-stimulating hormone (TSH), but not A23187, also stimulated Cl - transport. In conjunction with previous observations that Cl - transport was mediated by a bumetanidesensitive NaKCl 2 symporter on the basal membrane, these observations indicated the presence of a cyclic AMP activated Cl - conductance in the apical membrane of thyroid cells.