[Show abstract][Hide abstract] ABSTRACT: Thyroid dysfunction is a global health concern, causing defects including neurodevelopmental disorders, dwarfism and cardiac arrhythmia. Here, we show that the potassium channel subunits KCNQ1 and KCNE2 form a thyroid-stimulating hormone-stimulated, constitutively active, thyrocyte K+ channel required for normal thyroid hormone biosynthesis. Targeted disruption of Kcne2 in mice impaired thyroid iodide accumulation up to eightfold, impaired maternal milk ejection, halved milk tetraiodothyronine (T4) content and halved litter size. Kcne2-deficient mice had hypothyroidism, dwarfism, alopecia, goiter and cardiac abnormalities including hypertrophy, fibrosis, and reduced fractional shortening. The alopecia, dwarfism and cardiac abnormalities were alleviated by triiodothyronine (T3) and T4 administration to pups, by supplementing dams with T(4) before and after they gave birth or by feeding the pups exclusively from Kcne2+/+ dams; conversely, these symptoms were elicited in Kcne2+/+ pups by feeding exclusively from Kcne2-/- dams. These data provide a new potential therapeutic target for thyroid disorders and raise the possibility of an endocrine component to previously identified KCNE2- and KCNQ1-linked human cardiac arrhythmias.
[Show abstract][Hide abstract] ABSTRACT: Absorption of dietary iodide, presumably in the small intestine, is the first step in iodide (I(-)) utilization. From the bloodstream, I(-) is actively taken up via the Na(+)/I(-) symporter (NIS) in the thyroid for thyroid hormone biosynthesis and in such other tissues as lactating breast, which supplies I(-) to the newborn in the milk. The molecular basis for intestinal I(-) absorption is unknown. We sought to determine whether I(-) is actively accumulated by enterocytes and, if so, whether this process is mediated by NIS and regulated by I(-) itself. NIS expression was localized exclusively at the apical surface of rat and mouse enterocytes. In vivo intestine-to-blood transport of pertechnetate, a NIS substrate, was sensitive to the NIS inhibitor perchlorate. Brush border membrane vesicles accumulated I(-) in a sodium-dependent, perchlorate-sensitive manner with kinetic parameters similar to those of thyroid cells. NIS was expressed in intestinal epithelial cell line 6, and I(-) uptake in these cells was also kinetically similar to that in thyrocytes. I(-) downregulated NIS protein expression and its own NIS-mediated transport both in vitro and in vivo. We conclude that NIS is functionally expressed on the apical surface of enterocytes, where it mediates active I(-) accumulation. Therefore, NIS is a significant and possibly central component of the I(-) absorption system in the small intestine, a system of key importance for thyroid hormone biosynthesis and thus systemic intermediary metabolism.
No preview · Article · Feb 2009 · AJP Cell Physiology
[Show abstract][Hide abstract] ABSTRACT: In T cells anergy may be evoked by an unbalanced stimulation of the T-cell receptor in the absence of costimulation. Anergic T cells are unresponsive to new antigen receptor engagement and do not produce interleukin 2. We present evidence that anergizing stimuli induce changes in histone acetylation, which mediates transcriptional repression of interleukin 2 expression. In response to calcium signaling, anergic T cells up-regulate the expression of Ikaros, a zinc finger transcription factor essential for lymphoid lineage determination. Ikaros binds to the interleukin 2 promoter where it induces histone deacetylation. Confirming the role of Ikaros in the induction of T-cell anergy, cells with reduced Ikaros activity show defective inactivation in response to an anergizing stimulus. We propose a model in which tolerizing stimuli induce epigenetic changes on the interleukin 2 locus that are responsible for the stable inhibition of the expression of this cytokine in anergic T cells.
[Show abstract][Hide abstract] ABSTRACT: The sodium/iodide symporter (NIS) is a plasma membrane glycoprotein that mediates iodide (I-) transport in the thyroid, lactating breast, salivary glands, and stomach. Whereas NIS expression and regulation have been extensively investigated in healthy and neoplastic thyroid and breast tissues, little is known about NIS expression and function along the healthy and diseased gastrointestinal tract.
Thus, we investigated NIS expression by immunohistochemical analysis in 155 gastrointestinal tissue samples and by immunoblot analysis in 17 gastric tumors from 83 patients.
Regarding the healthy Gl tract, we observed NIS expression exclusively in the basolateral region of the gastric mucin-producing epithelial cells. In gastritis, positive NIS staining was observed in these cells both in the presence and absence of Helicobacter pylori. Significantly, NIS expression was absent in gastric cancer, independently of its histological type. Only focal faint NIS expression was detected in the direct vicinity of gastric tumors, i.e., in the histologically intact mucosa, the expression becoming gradually stronger and linear farther away from the tumor. Barrett mucosa with junctional and fundic-type columnar metaplasia displayed positive NIS staining, whereas Barrett mucosa with intestinal metaplasia was negative. NIS staining was also absent in intestinalized gastric polyps.
That NIS expression is markedly decreased or absent in case of intestinalization or malignant transformation of the gastric mucosa suggests that NIS may prove to be a significant tumor marker in the diagnosis and prognosis of gastric malignancies and also precancerous lesions such as Barrett mucosa, thus extending the medical significance of NIS beyond thyroid disease.
[Show abstract][Hide abstract] ABSTRACT: We report an extensive characterization of the Na(+)/monocarboxylate transporter (SMCT), a plasma membrane protein that mediates active transport of monocarboxylates such as propionate and nicotinate, and we show that SMCT may play a role in colorectal cancer diagnosis. SMCT, the product of the SLC5A8 gene, is 70% similar to the Na(+)/I(-) symporter, the protein that mediates active I(-) uptake in the basolateral surface of thyrocytes and other cells. SMCT was reported in the apical surface of thyrocytes and formerly proposed also to transport I(-) and was called the apical I(-) transporter. However, it is now clear that SMCT does not transport I(-). Here we demonstrate a high-affinity Na(+)-dependent monocarboxylate transport system in thyroid cells, which is likely to be SMCT. We show that, whereas thyroidal Na(+)/I(-) symporter expression is thyroid-stimulating hormone (TSH)-dependent and basolateral, SMCT expression is TSH-independent and apical not only in the thyroid but also in kidney and colon epithelial cells and in polarized Madin-Darby canine kidney cells. We determine the kinetic parameters of SMCT activity and show its inhibition by ibuprofen (K(i) = 73 +/- 9 microM) in Xenopus laevis oocytes. SMCT was proposed to be a tumor suppressor in colon cancer. Significantly, we show that higher expression of SMCT in colon samples from 113 colorectal cancer patients correlates with longer disease-free survival, suggesting that SMCT expression may be a favorable indicator of colorectal cancer prognosis.
Full-text · Article · Jun 2006 · Proceedings of the National Academy of Sciences