Specific staining of the thyroid follicular cell apical membrane by nitroblue tetrazolium

Cloning of two human thyroid cDNAs encoding new members of the NADPH oxidase family

Two cDNAs encoding NADPH oxidases and constituting the thyroid H(2)O(2) generating system have been cloned. The strategy of cloning was based on the functional similarities between H(2)O(2) generation in leukocytes and the thyroid, according to the hypothesis that one of the components of the thyroid system would belong to the gp91(Phox)/Mox1 gene family and display sequence similarities with gp91(Phox). Screening at low stringency with a gp91(Phox) probe of cDNA libraries from thyroid cells in primary culture yielded two distinct human cDNA clones harboring open reading frames of 1551 (ThOX1) and 1548 amino acids (ThOX2), respectively. The encoded polypeptides display 83% sequence similarity and are clearly related to gp91(Phox) (53 and 47% similarity). The theoretical molecular mass of 177 kDa is close to the apparent molecular mass of 180 kDa of the native corresponding porcine flavoprotein and the protein(s) detected by Western blot in dog and human thyroid. ThOX1 and ThOX2 display sequence similarities of 53% and 61%, respectively, with a predicted protein of Caenorhabditis elegans over their entire length. They show along their first 500 amino acids a similarity of 43% with thyroperoxidase. The corresponding genes of ThOX1 and ThOX2 are closely linked on chromosome 15q15.3. The dog mRNA expression is thyroid-specific and up-regulated by agents activating the cAMP pathway as is the synthesis of the polypeptides they are coding for. In human thyroid the positive regulation by cAMP is less pronounced. The proteins ThOX1 and ThOX2 accumulate at the apical membrane of thyrocytes and are co-localized with thyroperoxidase.

NADPH-dependent H2O2 generation catalyzed by thyroid plasma membranes. Studies with electron scavengers

Hog thyroid plasma membrane preparations containing a Ca2+-regulated NADPH-dependent H2O2-generating system were studied. The Ca2+-dependent reductase activities of ferricytochrome c, 2,6-dichloroindophenol, nitroblue tetrazolium, and potassium ferricyanide were tested and the effect of these scavengers on H2O2 formation, NADPH oxidation and O2 consumption were measured, with the following results. 1. Thyroid plasma membrane Ca2+-independent cytochrome c reduction was not catalyzed by the NADPH-dependent H2O2-generating system. This activity was superoxide-dismutase-insensitive. 2. Of the three other electron scavengers tested, only K3Fe(CN)6 was clearly, but partially reduced in a Ca2+-dependent manner. 3. Though the NADPH-dependent reduction of nitroblue tetrazolium was very low and superoxide-dismutase-insensitive, nitroblue tetrazolium inhibited O2 consumption, H2O2 formation and NADPH oxidation, indicating that nitroblue tetrazolium inhibits the H2O2-generating system. We conclude that the thyroid plasma membrane H2O2-generating system does not or liberate O2- and that Ca2+ controls the first step (NADPH oxidation) of the H2O2-generating system.

Modulation of thyroglobulin release by dog thyroid slices

Nonbutanol-extractable 131I (NBE131I) release by dog thyroid slices in vitro has been shown previously to be primarily thyroglobulin (Tg); it is stimulated by TSH. NBE131I (Tg) release has therefore been considered as an in vitro model of thyroglobulin secretion and was further characterized in this work. TSH-stimulated NBE131I (Tg) release, like TSH-stimulated BE131I (T4, T3 and iodide) release was reproduced by forskolin, an activator of adenylate cyclase. TSH-, (Bu)2cAMP- and forskolin-stimulated NBE131I (Tg) release was inhibited by 10(-5) M carbamylcholine, an effect relieved by 10(-5) M atropine, but not by 10(-4) M 1-methyl-3-isobutylxanthine. NBE131I (Tg) release was observed in the presence of 2 mM methimazole and 2 mM perchlorate. Cooling the slices to 20 degrees C or addition of 10(-5) M monensin completely blocked the formation of apical pseudopods and BE131I release but not NBE131I (Tg) release. Inhibition by 500 microM chloroquine of intralysosomal Tg hydrolysis and BE131I release did not enhance NBE131I (Tg) release. Cytochalasin B induced a concentration-dependent increase in basal and TSH-stimulated NBE131I (Tg) release at concentrations which depressed TSH-stimulated BE131I release. Removal of Ca2+ from the medium and slices by 10(-3) M or 10(-4) M EGTA increased NBE131I (Tg) release. In conclusion, in dog thyroid slices, TSH-stimulated NBE131I (Tg) release was mediated by cAMP and inhibited by 10(-5) M carbamylcholine at a step beyond cAMP. It was not neosynthesized Tg. It did not seem to require the formation of apical pseudopods or to result from the escape from lysosomes of undegraded thyroglobulin.(ABSTRACT TRUNCATED AT 250 WORDS)

Relation between thyroid peroxidase, H2O2 generating system and NADPH-dependent reductase activities in thyroid particulate fractions

In thyroid gland, iodination takes place on the apical plasma membrane and requires the presence of the thyroid peroxidase and H2O2 generating system. H2O2 generation and NBT (nitro blue tetrazolium) reductase activity (both of which are NADPH-dependent) as well as peroxidase activity were compared for their respective orientations in membrane vesicles. The possible role of NADPH-NBT reductase activity in H2O2 generation was also examined. Results favor the conclusion that thyroid peroxidase is oriented towards the luminal side of the vesicles, whereas the NADPH site of NADPH oxidase-dependent H2O2 generation is located on the external side of the same or of different vesicles. Furthermore, it is shown that different NADPH-NBT reductase activities are present on both the outer and inner surfaces of the membrane vesicles, and that none of these activities is able to produce either H2O2 or O-2. The idea that a multi-component complex is involved in H2O2 generation is discussed, and a model is proposed which takes into account the possible spatial separation of the thyroid peroxidase site from the NADPH site of this H2O2 generation system on the apical membrane of the thyrocyte.

Cytochemical localization of hydrogen peroxide generating sites in the rat thyroid gland

Sites of H2O2 generation in lightly prefixed, intact thyroid follicles were studied by two cytochemical reactions: peroxidase-dependent DAB oxidation and cerium precipitation. In both cases reaction product accumulated on the apical surface of the follicle cell at the membrane-colloid interface. The former reaction was inhibited by the peroxidase inhibitor, aminotriazole; both reactions were blocked by the presence of catalase. NADH in the medium slightly increased the amount of cerium precipitation. The ferricyanide technique for oxidoreductase activity was also applied; reaction product again was associated with the apical surface. These results strongly imply that the follicle cells have a NADH oxidizing system generating H2O2 at the apical plasma membrane.

NADPH-dependent H2O2 generation and peroxidase activity in thyroid particular fraction

A NADPH-dependent H2O2 generating system associated with a thyroid particular fraction is described. H2O2 is measured by two different methods: iodination of NADPH itself when the system is supplemented with lactoperoxidase and [125I]iodide, and by the scopoletin method. It is shown that: H2O2 generation is inhibited by catalase and is dependent on NADPH or particulate protein concentration; radical scavengers of OH and of singlet oxygen have no effect while superoxide dismutase has only a marginal effect; disruption of the particular fraction by phospholipase A2 or digitonin treatment completely abolished H2O2 generation activity while thyroid peroxidase activity appears, suggesting different sites for the two activities in the membrane vesicles.

The effect of cell damage on the density and steroidogenic capacity of rat testis Leydig cells, using an NADH exclusion test for determination of viability

The ability of cells to exclude pyridine nucleotides was found to be a more sensitive index of cell viability than trypan blue. The three nucleated cell bands obtained by centrifugation of crude rat testis cells on Percoll density gradients contained different proportions of viable and damaged cells. Band III, the steroidogenically active Leydig cell band was mainly viable cells, whilst bands I and II contained 70 and 35% damaged cells respectively. Leydig cells damaged by freezing were shown to have a lower density than viable Leydig cells and did not produce testosterone after stimulation with LH. It is concluded that the methods used to prepare and purify rat testis Leydig cells contribute to the apparent Leydig cell "heterogeneity".