The Pervasive Effects of ER Stress on a Typical Endocrine Cell: Dedifferentiation, Mesenchymal Shift and Antioxidant Response in the Thyrocyte.

The endoplasmic reticulum stress and the unfolded protein response are triggered following an imbalance between protein load and protein folding. Until recently, two possible outcomes of the unfolded protein response have been considered: life or death. We sought to substantiate a third alternative, dedifferentiation, mesenchymal shift, and activation of the antioxidant response by using typical endocrine cells, i.e. thyroid cells. The thyroid is a unique system both of endoplasmic reticulum stress (a single protein, thyroglobulin represents the majority of proteins synthesized in the endoplasmic reticulum by the thyrocyte) and of polarized epithelium (the single layer of thyrocytes delimiting the follicle). Following endoplasmic reticulum stress, in thyroid cells the folding of thyroglobulin was disrupted. The mRNAs of unfolded protein response were induced or spliced (X-box binding protein-1). Differentiation was inhibited: mRNA levels of thyroid specific genes, and of thyroid transcription factors were dramatically downregulated, at least in part, transcriptionally. The dedifferentiating response was accompanied by an upregulation of mRNAs of antioxidant genes. Moreover, cadherin-1, and the thyroid (and kidney)-specific cadherin-16 mRNAs were downregulated, vimentin, and SNAI1 mRNAs were upregulated. In addition, loss of cortical actin and stress fibers formation were observed. Together, these data indicate that ER stress in thyroid cells induces dedifferentiation, loss of epithelial organization, shift towards a mesenchymal phenotype, and activation of the antioxidant response, highlighting, at the same time, a new and wide strategy to achieve survival following ER stress, and, as a sort of the other side of the coin, a possible new molecular mechanism of decline/loss of function leading to a deficit of thyroid hormones formation.

Iodine status assessment in Campania (Italy) as determined by urinary iodine excretion.

OBJECTIVE: Mild iodine deficiency was first documented in Campania in the 1990s. We assessed the urinary iodine nutritional status of schoolchildren in Campania before the introduction of legislation for salt iodization and compared the findings with previous results to evaluate to what extent "silent" iodine prophylaxis, which accompanies socioeconomic advances, affects iodine status. METHODS: We examined 10552 schoolchildren aged 9-13 y from the five Campania provinces. The study was conducted from April 1999 to October 2002. Urinary iodine excretion was measured in morning urine samples with the AutoAnalyzer 3, an automated system based on the Sandell-Kolthoff reaction. Data were interpreted according to World Health Organization criteria. RESULTS: The median urinary iodine excretion level in Campania was less than 100 micromicrog/L, which indicates insufficient iodine intake. Mild iodine deficiency was identified in all provinces, namely Napoli, Salerno, Caserta, Avellino, and Benevento, with median urinary iodine excretions of 87, 81, 72, 64, and 61 microg/L, respectively. Overall, the analysis of frequency distribution showed values below 50 and 100 microg/L in 32% and 61% of children, respectively. These values were lower than those previously reported for Campania. CONCLUSION: This study confirms that Campania is a mild iodine deficiency area. The decrease in iodine deficiency versus previous studies indicates that silent prophylaxis plays a relevant role in this condition, but it is not sufficient to eradicate it. Our data will serve as a basis for future evaluations of iodine status in Campania.

Targeting of PED/PEA-15 molecular interaction with phospholipase D1 enhances insulin sensitivity in skeletal muscle cells.

Phosphoprotein enriched in diabetes/phosphoprotein enriched in astrocytes (PED/PEA-15) is overexpressed in several tissues of individuals affected by type 2 diabetes. In intact cells and in transgenic animal models, PED/PEA-15 overexpression impairs insulin regulation of glucose transport, and this is mediated by its interaction with the C-terminal D4 domain of phospholipase D1 (PLD1) and the consequent increase of protein kinase C-alpha activity. Here we show that interfering with the interaction of PED/PEA-15 with PLD1 in L6 skeletal muscle cells overexpressing PED/PEA-15 (L6(PED/PEA-15)) restores insulin sensitivity. Surface plasmon resonance and ELISA-like assays show that PED/PEA-15 binds in vitro the D4 domain with high affinity (K(D) = 0.37 +/- 0.13 mum), and a PED/PEA-15 peptide, spanning residues 1-24, PED-(1-24), is able to compete with the PED/PEA-15-D4 recognition. When loaded into L6(PED/PEA-15) cells and in myocytes derived from PED/PEA-15-overexpressing transgenic mice, PED-(1-24) abrogates the PED/PEA-15-PLD1 interaction and reduces protein kinase C-alpha activity to levels similar to controls. Importantly, the peptide restores insulin-stimulated glucose uptake by approximately 70%. Similar results are obtained by expression of D4 in L6(PED/PEA-15). All these findings suggest that disruption of the PED/PEA-15-PLD1 molecular interaction enhances insulin sensitivity in skeletal muscle cells and indicate that PED/PEA-15 as an important target for type 2 diabetes.

ER stress is associated with dedifferentiation and an epithelial-to-mesenchymal transition-like phenotype in PC Cl3 thyroid cells.

Conditions perturbing the homeostasis of the endoplasmic reticulum (ER) cause accumulation of unfolded proteins and trigger ER stress. In PC Cl3 thyroid cells, thapsigargin and tunicamycin interfered with the folding of thyroglobulin, causing accumulation of this very large secretory glycoprotein in the ER. Consequently, mRNAs encoding BiP and XBP-1 were induced and spliced, respectively. In the absence of apoptosis, differentiation of PC Cl3 cells was inhibited. mRNA and protein levels of the thyroid-specific genes encoding thyroglobulin, thyroperoxidase and the sodium/iodide symporter and of the genes encoding the thyroid transcription factors TTF-1, TTF-2 and Pax-8 were dramatically downregulated. These effects were, at least in part, transcriptional. Moreover, they were selective and temporally distinct from the general and transient PERK-dependent translational inhibition. Thyroid dedifferentiation was accompanied by changes in the organization of the polarized epithelial monolayer. Downregulation of the mRNA encoding E-cadherin, and upregulation of the mRNAs encoding vimentin, alpha-smooth muscle actin, alpha(1)(I) collagen and SNAI1/SIP1, together with formation of actin stress fibers and loss of trans-epithelial resistance were found, confirming an epithelial-mesenchymal transition (EMT). The thyroid-specific and epithelial dedifferentiation by thapsigargin or tunicamycin were completely prevented by the PP2 inhibitor of Src-family kinases and by stable expression of a dominant-negative Src. Together, these data indicate that ER stress induces dedifferentiation and an EMT-like phenotype in thyroid cells through a Src-mediated signaling pathway.

Oncogenic and anti-apoptotic activity of NF-kappa B in human thyroid carcinomas.

Thyroid cancer includes three types of carcinomas classified as differentiated thyroid carcinomas (DTC), medullary thyroid carcinomas, and undifferentiated carcinomas (UTC). DTC and medullary thyroid carcinomas generally have a good prognosis, but UTC are usually fatal. Consequently, there is a need for new effective therapeutic modalities to improve the survival of UTC patients. Here we show that NF-kappa B is activated in human thyroid neoplasms, particularly in undifferentiated carcinomas. Thyroid cell lines, reproducing in vitro the different thyroid neoplasias, also show basal NF-kappa B activity and resistance to drug-induced apoptosis, which correlates with the level of NF-kappa B activation. Activation of NF-kappa B in the DTC cell line NPA renders these cells resistant to drug-induced apoptosis. Stable expression of a super-repressor form of I kappa B alpha (I kappa B alpha M) in the UTC cell line FRO results in enhanced sensitivity to drug-induced apoptosis, to the loss of the ability of these cells to form colonies in soft agar, and to induce tumor growth in nude mice. In addition, we show that FRO cells display a very low JNK activity that is restored in FRO-I kappa B alpha M clones. Moreover, inhibition of JNK activity renders FRO-I kappa B alpha M clones resistant to apoptosis induced by chemotherapeutic agents. Our results indicate that NF-kappa B plays a pivotal role in thyroid carcinogenesis, being required for tumor growth and for resistance to drug-induced apoptosis, the latter function very likely through the inhibition of JNK activity. Furthermore, the strong constitutive NF-kappa B activity in human anaplastic thyroid carcinomas, besides representing a novel diagnostic tool, makes NF-kappa B a target for the development of novel therapeutic strategies.

TSH/cAMP up-regulate sarco/endoplasmic reticulum Ca2+-ATPases expression and activity in PC Cl3 thyroid cells.

OBJECTIVE: We recently reported that the sarco/endoplasmic reticulum Ca2+-ATPase (SERCA) 2b is the SERCA form preferentially expressed in rat thyroid. Moreover, SERCA2b expression dramatically decreases in virally transformed, highly tumorigenic, PC Cl3 thyroid cells. These results suggest that, in the thyroid, SERCA2b, in addition to its housekeeping role, is linked to differentiation and is a regulated gene. We therefore sought to study the effect of TSH, the main regulator of thyroid function, on SERCA2b expression and activity. METHODS: PC Cl3 cells were hormone starved in low-serum medium and stimulated for long (48 h) or short (1, 2 and 4 h) times. SERCA2b expression and activity were evaluated by Northern and Western blots, Ca2+-ATPase activity and Ca2+ store content. RESULTS: In PC Cl3 cells, SERCA2b mRNA and protein were induced twofold by a 48-h long treatment with TSH. Long-term elevation (48 h) of intracellular cAMP levels, by forskolin or 8-Br-cAMP, had similar effects on SERCA2b mRNA and protein. We also measured Ca2+-ATPase activity and Ca2+ store content. Both long (48 h) and short (0.5-1 h) treatments with TSH, forskolin or 8-Br-cAMP induced a marked increase of SERCA2b activity. This effect was completely abolished by H89, a specific inhibitor of cAMP-dependent protein kinase A (PKA). TSH and 8-Br-cAMP increased Ca2+ store content after both long (48 h) and short (1-2 h) treatments. CONCLUSIONS: These data suggested that TSH/cAMP acts as an important regulator of both SERCA2b expression and activity in the thyroid system, through PKA activation.

Physical and functional interaction of CARMA1 and CARMA3 with Ikappa kinase gamma-NFkappaB essential modulator.

CARMA proteins are scaffold molecules that contain a caspase recruitment domain and a membrane-associated guanylate kinase-like domain. CARMA1 plays a critical role in mediating activation of the NFkappaB transcription factor following antigen receptor stimulation of both B and T lymphocytes. However, the biochemical mechanism by which CARMA1 regulates activation of NFkappaB remains to be determined. Here we have shown that CARMA1 and CARMA3 physically associate with Ikappa kinase gamma/NFkappaB essential modulator (IkappaKgamma-NEMO) in lymphoid and non-lymphoid cells. CARMA1 participates to an inducible large molecular complex that contains IkappaKgamma/NEMO, Bcl10, and IkappaKalpha/beta kinases. Expression of the NEMO-binding region of CARMA3 exerts a dominant negative effect on Bcl10-mediated activation of NFkappaB. Thus, our results provide direct evidence for physical and functional interaction between CARMA and the IkappaK complex and offer a biochemical framework to understand the molecular activities controlled by CARMA-1, -2, and -3 and Bcl10.

The RHL-1 subunit of the asialoglycoprotein receptor of thyroid cells: cellular localization and its role in thyroglobulin endocytosis.

The rat hepatic lectin (RHL)-1 is the major component of the rat liver asialoglycoprotein receptor (ASGPr), a membrane receptor highly expressed on the basolateral side of hepatocytes, which mediates endocytosis of serum desialated glycoproteins. We have recently shown that RHL-1 is expressed in rat thyroid tissue and thyroid differentiated cell lines. Both in vitro and in vivo assays show that thyrotropin up-regulates thyroid RHL-1 expression, while neoplastic transformation of thyroid cells exerts a down-regulation of receptor expression. Moreover, RHL-1 expressed on the surface of differentiated thyroid cells is able to bind thyroglobulin (Tg), the macromolecular site of synthesis and storage of thyroid hormones. In the present work, we demonstrate, by immunohistochemistry analysis, that RHL-1 is localized on the apical surface of thyrocytes, at a variance with its basolateral localization on hepatocytes. Moreover, albeit its expression in thyroid is less abundant than in liver, the receptor is able to bind asialorosomucoid (ASOR), the best-known ligand of hepatic ASGPr, and to mediate endocytosis of a significative amount of Tg on the surface of differentiated PC Cl3 thyroid cells. Taken together, the data suggest that RHL-1, even if expressed in thyroid at lower levels than in liver, could serve as a receptor for endocytosis of colloidal Tg and, likely, for its delivery to lysosomes.

Promoter identification of CIKS, a novel NF-kappaB activating gene, and regulation of its expression.

We have recently identified a novel gene, named CIKS (Connection to IKK-complex and SAPK), able to activate the transcription factor NF-kappaB, after interaction with the regulatory subunit NEMO/IKKgamma of IKK complex, and the stress-activated protein kinase (SAPK)/JNK. CIKS mRNA is ubiquitously expressed, although its levels differ greatly among different tissues. The aim of this study is to identify and characterize the promoter region of CIKS gene and to analyse the regulation of its expression by different cytokines. The transcription start site of CIKS mRNA was mapped both by primer extension and by a polymerase chain reaction (PCR)-based strategy. The proximal 5'-flanking region of CIKS gene was 'TATA-less', but contained other consensus promoter elements including an initiator (Inr), 'GC' and 'CAAT' boxes. Transfection of luciferase reporter plasmids containing 1.8 kb of the 5'-flanking region increased luciferase activity in epithelial MDCK cells, but not in endothelial HUVEC cells. Deletion analysis identified a sequence from -464 to -220 bp of the 5'-flanking region of CIKS gene essential for basal promoter activity in MDCK cells. Competitive reverse transcriptase-PCR, Northern and Western blot assays showed that different cytokines, such as tumor necrosis factor (TNF)-alpha, Interleukin (IL)-1beta and transforming growth factor (TGF)-beta, dramatically increased CIKS mRNA expression in HeLa cells. We conclude that the proximal 5'-flanking region of CIKS gene contains a functional promoter and binding sites for nuclear proteins leading to its basal transcription. Moreover, we demonstrate that the expression of CIKS is up-regulated by different cytokines.

Folding of thyroglobulin in the calnexin/calreticulin pathway and its alteration by loss of Ca2+ from the endoplasmic reticulum.

During its initial folding in the endoplasmic reticulum (ER), newly synthesized thyroglobulin (Tg) is known to interact with calnexin and other ER molecular chaperones, but its interaction with calreticulin has not been examined previously. In the present study, we have investigated the interactions of endogenous Tg with calreticulin and with several other ER chaperones. We find that, in FRTL-5 and PC-Cl3 cells, calnexin and calreticulin interact with newly synthesized Tg in a carbohydrate-dependent manner, with largely overlapping kinetics that are concomitant with the maturation of Tg intrachain disulphide bonds, preceding Tg dimerization and exit from the ER. Calreticulin co-precipitates more newly synthesized Tg than does calnexin; however, using two different experimental approaches, calnexin and calreticulin were found in ternary complexes with Tg, making this the first endogenous protein reported in ternary complexes with calnexin and calreticulin in the ER of live cells. Depletion of Ca(2+) from the ER elicited by thapsigargin (a specific inhibitor of ER Ca(2+)-ATPases) results in retention of Tg in this organelle. Interestingly, thapsigargin treatment induces the premature exit of Tg from the calnexin/calreticulin cycle, while stabilizing and prolonging interactions of Tg with BiP (immunoglobulin heavy chain binding protein) and GRP94 (glucose-regulated protein 94), two chaperones whose binding is not carbohydrate-dependent. Our results suggest that calnexin and calreticulin, acting in ternary complexes with a large glycoprotein substrate such as Tg, might be engaged in the folding of distinct domains, and indicate that lumenal Ca(2+) strongly influences the folding of exportable glycoproteins, in part by regulating the balance of substrate binding to different molecular chaperone systems within the ER.

Endoplasmic reticulum stress causes thyroglobulin retention in this organelle and triggers activation of nuclear factor-kappa B via tumor necrosis factor receptor-associated factor 2.

Perturbing the endoplasmic reticulum homeostasis of thyroid cell lines with thapsigargin, a specific inhibitor of the sarcoendoplasmic reticulum Ca(2+) adenosine triphosphatases, and tunicamycin, an inhibitor of the N-linked glycosylation, blocked Tg in the endoplasmic reticulum. This event was signaled outside the endoplasmic reticulum and resulted in activation of the c-Jun N-terminal kinase (JNK)/stress-activated protein kinase and nuclear factor-kappa B (NF-kappa B) stress response pathways. Activation of the JNK/stress-activated protein kinase signaling pathway was assessed by measuring the amount of phospho-JNK and the activity of JNK by kinase assays. Activation of the NF-kappa B signaling pathway was assessed by measuring the level of inhibitory subunit I kappa B alpha, DNA binding, and transcriptional activity of NF-kappa B. Cycloheximide treatment, at a dose able to profoundly inhibit protein synthesis in FRTL-5 cells, obliterated the decrease in the level of the inhibitory subunit I kappa B alpha produced by thapsigargin and tunicamycin. Therefore, protein synthesis was required to generate a signal from stressed endoplasmic reticulum. This substantiates the hypothesis that endoplasmic reticulum retention of newly synthesized Tg and other cargo (secretory and membrane) proteins functions upstream of signal activation. Dominant negative TNF receptor-associated factor 2 (TRAF2) inhibited activation of NF-kappa B, which was also inhibited in embryonic fibroblasts derived from TRAF2(-/-) mice, respect to their normal counterpart. These data extend the recent demonstration that TRAF2 mediated JNK activation in response to endoplasmic reticulum stress and strongly strengthened the idea that endogenous stress signals initiated in the endoplasmic reticulum proceed by a pathway similar to that initiated by plasma membrane receptors in response to extracellular signals.