The properties of TSH-dependent iodide (I−) uptake are defined for a cloned, continuously growing, functioning rat thyroid cell line (FRTL-5 cells). Since these cells grow without a lumen and are therefore restricted in their ability to iodinate thyroglobulin, the FRTL-5 cells offer the opportunity to directly study transport processes across the membrane into the cell as well as the process whereby I− moves from the cell. FRTL-5 cells concentrate I− approximately 30-fold and exhibit many of the properties of I− uptake seen in thyroid tissue slice and primary cell culture systems. In these cells, accumulation of I− is consistent with a Na+-dependent carrier model for I− uptake, and effects on the infux and efflux processes can be dissociated. Because FRTL-5 cells can be maintained in culture indefinitely and can provide large quantities of a homogeneous functional thyroid cell preparation for study, these cells offer the unique opportunity to further define the mechanism and kinetics of I− transport in a ...

Iodide transport in a continuous line of cultured cells from rat thyroid.

Using a clonal line of TSH-dependent functional rat thyroid cells, the effects of TSH on cAMP production and cell growth, as measured by cell number and [14C]thymidine incorporation, were compared. The withdrawal of TSH from the medium stopped the growth of cells, as measured by cell number. After 24 h in TSH-free medium, an acute challenge with 1 × 10-11 M pure TSH caused a 40-fold increase in the cAMP level; this response increased to greater than 80-fold as TSH withdrawal from the culture system was prolonged over 10 days. In contrast to these acute effects on cAMP levels, an increase in [14C]thymidine incorporation required 20-fold higher TSH concentrations and waned to an unresponsive level after 10 days of TSH withdrawal. After withdrawal of TSH from the medium for 10 days, readdition of TSH could return cell growth to normal rates only after a 2-day lag period. In terms of the lag, the TSH effect on cell number was paralleled by its effect on thymidine incorporation, not cAMP levels; (Bu)2-cAMP at ...

The relationship of growth and adenylate cyclase activity in cultured thyroid cells: separate bioeffects of thyrotropin.

Pam Fredman Psychiatrie Research Centre, Department of Neurochemistry, University of Göteborg, St. Jörgen Hospital, S-422 03 HISINGS BACKA, Sweden A new anion exchange resin, Spherosil-DEAE-Dextran, built on porous glass beads covered with crosslinked DEAE-Dextran, has been compared with other resins, DEAE-Sephacel, DEAE-Sephadex and DEAESepharose, regarding its value in the isolation and separation of gangliosides from a crude ganglioside extract. In comparison with the best cornmercial resin, DEAE-Sepharose, Spherosil-DEAE-Dextran had higher binding capacity, higher binding specificity and gave a better separation of gangliosides with four and five sialic acids. The constant bed volume facilitated regeneration. Gangliosides were separated according to the number of sialic acids by stepwise elution with potassium acetate in methanol. The elution scheme was used for both large and small scale separation. Separation of gangliosides on anion exchange res ins according to their number of sialic acids results in a better discrimination and identification of the many closely allied gangliosides. This property is particularly important in the separation of gangliosides with a wide variation in the substitution of the sialic acid, N-acetyl, N-glycolyl or N,O-diacetyl groups. An N,O-diacetyl sialic acid will exhibit chemical properties very similar to those of a ganglioside with the N-acetyl sialic acid in lacton form, but they could be separated on the anion exchanger. 'his study was performed in collaboration with O. Nilsson and L. Svennerholm, Psychiatrie Research Centre, and J.L. Tayot, Institute Merieux, Lyon. It was supported by grants from the Swedish Medical Research Council (3X-627) and the Medical Faculty, University of Göteborg.

Structure and function of gangliosides

Gangliosides inhibit 125I-labeled thyrotropin binding to the thyrotropin receptors on bovine thyroid plas- ma membranes, on guinea pig retro-orbital tissue plasma membranes, and on human adipocyte membranes. This inhi- bition by gangliosides is critically altered by the number and location of the sialic acid residues within the ganglioside structure, the efficacy of inhibition having the following order: GDlb > GT1 > GM1 > GM2 = GM3 > GDla The inhibi- tion results from the interaction of thyrotropin and ganglios- ides, rather than the interaction of membrane and ganglios- ides. Fluorescence studies show that the inhibition is associ- ated with a distinct conformational change of the thyrotro- pin molecule and that the progression from a "noninhibitory conformation" to an "inhibitory conformation" arallels ex- actly the order of effectiveness in inhibiting 125I-Yabeled thy- rotropin binding. The ganglioside inhibition of 125I-labeled thyrotropin binding appears to be hormonally specific in that it is not affected by albumin, glucagon, insulin, prolactin, fol- licle-stimulating hormone, growth hormone, or corticotropin. The possibility that a ganglioside or ganglioside-like struc- ture is a component of the thyrotropin receptor is suggested by the finding that gangliosides more complex than N-acetyl- neuraminylgalactosylglucosylceramide are present in bovine thyroid membranes in much higher quantities than have been previously found in extraneural tissue. The finding that the B component of cholera toxin, which also interacts with gangliosides, has a peptide sequence in common with the : subunit of thyrotropin, suggests that thyrotropin and cholera toxin may be analogous in their mode of action on the mem- brane.

Thyrotropin-ganglioside interactions and their relationship to the structure and function of thyrotropin receptors (hormone mechanism/cholera toxin/luteinizing hormone/human chorionic gonadotropin/adenylate cyclase)

We recently demonstrated in an immortalized thyroid cell line that integrin stimulation by fibronectin (FN) simultaneously activates two signaling pathways: Ras/Raf/MAPK kinase (Mek)/Erk and calcium Ca2+/calcium calmodulin-dependent kinase II (CaMKII). Both signals are necessary to stimulate Erk phosphorylation because CaMKII modulates Ras-induced Raf-1 activity. In this study we present evidence that extends these findings to normal human thyroid cells in primary culture, demonstrating its biological significance in a more physiological cell model. In normal thyroid cells, immobilized FN-induced activation of p21Ras and Erk phosphorylation. This pathway was responsible for FN-induced cell proliferation. Concurrent increase of intracellular Ca2+ concentration and CaMKII activation was observed. Both induction of p21Ras activity and increase of intracellular Ca2+ concentration were mediated by FN binding to alphavbeta3 integrin. Inhibition of the Ca2+/CaMKII signal pathway by calmodulin or CaMKII inhibitors completely abolished the FN-induced Erk phosphorylation. Binding to FN induced Raf-1 and CaMKII to form a protein complex, indicating that intersection between Ras/Raf/Mek/Erk and Ca2+/CaMKII signaling pathways occurred at Raf-1 level. Interruption of the Ca2+/CaMKII signal pathway arrested cell proliferation induced by FN. We also analyzed thyroid tumor cell lines that displayed concomitant aberrant integrin expression and signal transduction. These data confirm that integrin activation by FN in normal thyroid cells generates Ras/Raf/Mek/Erk and Ca2+/CaMKII signaling pathways and that both are necessary to stimulate cell proliferation, whereas in thyroid tumors integrin signaling is altered.

Fibronectin-Induced Proliferation in Thyroid Cells Is Mediated by αvβ3 Integrin through Ras/Raf-1/MEK/ERK and Calcium/CaMKII Signals

When grown in the presence of thyrotropin, dog thyroid cells in culture form follicle-like structures, take up labeled iodide, and iodinate macromolecular components in the cell. When grown in the absence of thyrotropin, dog thyroid cells in culture form a monolayer, take up only 6% of the iodide of follicular cells, and do not iodinate macromolelcular components in the cell. The iodide uptake in monolayer cells does, however, reflect an incorporation process unique to thyroid cells because hepatocytes and fibroblasts do not have the capacity of the monolayer cells to take up iodide. Thyrotropin stimulation of monolayer cells for a prolonged period (3–8 days) causes the cAMP levels of these cells to return to levels identical to those in follicular cells. The increased cAMP levels are not due to the induction of an adenylate cyclase enzyme, because homogenates of monolayer cells have a thyrotropinstimulable adenylate cyclase activity. The low level of cAMP, thus, seems to be a problem of receptor coupling...

Effects of Thyrotropin on Iodine Metabolism of Dog Thyroid Cells in Tissue Culture

Synthesis of basement membrane components by differentiated thyroid cells

Messenger RNA properties of primary cultures of thyroid cells isolated from normal thyroid tissue and from patients with various thyroid diseases.

Effect of thyrotropin on the properties of messenger RNA from cultured human thyroid cells

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Effects of Thyrotropin on Iodine Metabolism of Dog Thyroid Cells in Tissue Culture

Synthesis of basement membrane components by differentiated thyroid cells

Messenger RNA properties of primary cultures of thyroid cells isolated from normal thyroid tissue and from patients with various thyroid diseases.

Effect of thyrotropin on the properties of messenger RNA from cultured human thyroid cells