No abstract

Secretogranin II (SgII) is one of the three major proteins, the other two being chromogranins A (CGA) and B (CGB), of secretory granules of neuroendocrine cells. The Ca(2+) storage proteins CGA and CGB not only are coupled to the IP(3) receptor (IP(3)R)/Ca(2+) channels that exist on the secretory granule membrane but also are known to play key roles in secretory granule biogenesis. Unlike the better studied CGA and CGB, secretogranin II has never been completely purified in the native state and studied. We have therefore purified SgII in native form from bovine adrenal medulla and subjected it to biochemical characterization. Secretogranin II consisted of largely beta-sheet and random coil structures with a low level of alpha-helicity. Like CGA and CGB, it also underwent pH-dependent conformational changes, showing 9.5% alpha-helicity at pH 7.5 and 17.0% alpha-helicity at pH 5.5. Secretogranin II also underwent acidic pH- and Ca(2+)-dependent aggregation, and it was approximately 8-fold more sensitive than CGA to Ca(2+) in its pH-dependent aggregation but was 8-fold less sensitive than CGB. Further, similar to CGA and CGB that had interacted with the secretory granule membrane at the intragranular pH 5.5, SgII also interacted with the secretory granule membrane at pH 5.5 and dissociated from it at near-physiological pH 7.5, implying similar roles of SgII in the cell as those of CGA and CGB. Secretogranin II hence appeared to actively participate in secretory granule biogenesis as has been proposed for CGA and CGB.

TSH is an important physiological regulator of growth and function in thyroid gland. The mechanism of action of TSH depends on interaction with its receptor coupled to heterotrimeric G proteins. We show here that TSH induces the phosphorylation of tyrosine in the intracellular kinases Janus kinase 1 (JAK1) and -2 (JAK2) in rat thyroid cells and in Chinese hamster ovary (CHO) cells transfected with human TSH receptor (TSHR). The JAK family substrates STAT3 (signal transducers and activators of transcription) are rapidly tyrosine phosphorylated in response to TSH. We also find that JAK1, JAK2, and STAT3 coprecipitate with the TSHR, indicating that the TSHR may be able to signal through the intracellular phosphorylation pathway used by the JAK-STAT cascade. TSH increases STAT3-mediated promoter activity and also induces endogenous SOCS-1 (suppressor of cytokine signaling-1) gene expression, a known target gene of STAT3. The expression of a dominant negative form of STAT3 completely inhibited TSH-mediated SOCS-1 expression. These findings suggest that the TSHR is able to signal through JAK/STAT3 pathways.

Chromogranins A (CGA) and B (CGB) are two major Ca 2؉ storage proteins of the secretory granules of neuroendocrine cells. Nevertheless, we found in the present study that CGB was also localized in the nucleus. In immunogold electron microscopy using bovine adrenal medullary chromaffin cells, it was found that the number of CGB-labeled gold particles localized per m 2 of the nucleus was equivalent to 20% that of CGB-labeled gold particles localized per m 2 of the secretory granules. Considering that CGB is estimated to exist in the 0.1-0.2-mM range in the secretory granules of bovine chromaffin cells, 20% of these amounts to 20 -40 M. In addition, transfection of CGA and CGB into nonneuroendocrine COS-7 and NIH3T3 cells repeatedly indicated the nuclear localization of CGB in addition to its usual localization in the cytoplasm. Moreover, immunoblot and immunogold electron microscopy analyses of neuroendocrine PC12 cells also showed the existence of endogenous CGB in both the cytosol and the nucleus. Nuclear routing of CGB did not appear to depend entirely upon the nuclear localization signal as some of the nuclear localization signal mutant CGB were still targeted to the nucleus. In gene array assay, CGB was shown to either induce or suppress transcription of many genes including those of transcription factors. Of these we have analyzed eight genes, four induced (zinc finger protein, MEF2C, hCRP2, abLIM) and four suppressed (hcKrox, T3-receptor, troponin C, integrin) using the quantitative reverse transcription-PCR method and spectrophotometry to determine the transcription levels of each mRNA. CGB was shown to increase the transcription of zinc finger protein, MEF2C, hCRP2, and abLIM by 2.5-5-fold while suppressing that of hcKrox, T3-receptor, troponin C, and integrin by 60 -75%. Given that MEF2C and hcKrox genes are transcription factors, these results pointed to the transcription control role of CGB in the nucleus.The secretory granules of neuroendocrine cells are loaded with hormones, neurotransmitters, and ions such as Ca 2ϩ , Mg 2ϩ , and Zn 2ϩ along with peptides and proteins of which chromogranins A and B are the most abundant (1-5). Chromogranins A and B are acidic proteins (1-5) with acidic residues constituting 25-30% of the amino acid residues (6 -12), and this high content of negatively charged amino acid residues is thought to be responsible for the high capacity, low affinity Ca 2ϩ binding property of chromogranins (13,14), binding 32-93 mol of Ca 2ϩ /mol (14, 15). The comparison of the amino acid sequences of CGA 1 (6 -8) and CGB (9 -12) shows little sequence homology except the two conserved regions, one near the N-terminal region bordered by two cysteine residues (residues 17-38 in bovine CGA and 16 -37 in bovine CGB) and the other the C-terminal region (residues 409 -431 in bovine CGA and 604 -626 in bovine CGB). Despite the differences in amino acid sequences, chromogranins A and B and secretogranin II (also called chromogranin C) were shown to aggregate in an acidic pH and high calcium environm...

A cDNA, mSOD1, encoding cytosolic copper/ zinc superoxide dismutase (CuZnSOD) was cloned and characterized from cell cultures of cassava (Manihot esculenta Crantz) which produce a high yield of SOD. mSOD1 encodes a 152-amino acid polypeptide with a pI value of 5.84. Southern analysis using an mSOD1-speci®c probe indicated that a single copy of the mSOD1 gene is present in the cassava genome. The mSOD1 gene is highly expressed in cultured cells, as well as in intact stems and tuberous roots. It is expressed at a low level in leaves and petioles. Transcripts of mSOD1 were not detected in nontuberous roots. Transcriptional level of mSOD1 reaches a high level at stationary phase, and then sharply decreases during further culture. In excised cassava leaves, the mSOD1 gene responded to various stresses in dierent ways. The stresses tested included changes in temperature and exposure to stress-inducing chemicals. Levels of mSOD1 transcript increased dramatically a few hours after heat stress at 37°C and showed a synergistic eect with wounding stress. Levels decreased in response to chilling stress at 4°C and showed an antagonistic eect with wounding stress. The gene was induced by abscisic acid, ethephon, NaCl, sucrose, and methyl viologen. These results indicate that the mSOD1 gene is involved in the response to oxidative stress induced by environmental change.

Intercellular adhesion molecule-1 (ICAM-1) has been suggested to play an important role in the perpetuation of autoimmune thyroid disease. To clarify the regulation of ICAM-1 gene in thyroid cells, we investigated ICAM-1 expression in the FRTL-5 thyroid cell model and defined several elements in the 5'-regulatory region that are important for transcriptional regulation of the rat ICAM-1 gene. Cells maintained in medium with 5% serum but without hydrocortisone, insulin, and thyrotropin (TSH) express the highest levels of ICAM-1 RNA. TSH/forskolin downregulate ICAM-1 RNA levels independent of the presence or absence of hydrocortisone or insulin. Moreover, TSH/forskolin decrease ICAM-1 RNA levels that are maximally induced by two cytokines: 100 ng/mL tumor necrosis factor-alpha (TNF-alpha) or 100 U/ml interferon-gamma (IFN-gamma). The effect of TSH/forskolin, as well as TNF-alpha and IFN-gamma, on ICAM-1 RNA levels is transcriptional. Thus, we cloned a 1.8-kb fragment of the 5'-flanking region of the rat ICAM-1 gene, upstream of the translational start site, and showed that TNF-alpha or IFN-gamma caused a 3.5- and greater than 12-fold increase respectively, in its promoter activity, when linked to a luciferase reporter gene and stably transfected into FRTL-5 cells. TSH or forskolin, in contrast, halved the activity of the full length chimera within 24 hours and significantly suppressed the TNF-alpha and IFN-gamma-induced increase (>50%; p < 0.02). Using 5'-deletion mutants, we located the element important for the TNF-alpha effect between -431 and -175 bp; we additionally show that deletion of a NF-kappaB core element within this region, TTGGAAATTC (-240 to -230 bp), causes the loss of TNF-alpha inducibility. The effect of IFN-gamma could be localized between -175 bp and -97 bp from the start of translation. This region contains 2 regulatory elements known to be involved in IFN-gamma action in other eukaryotic cells, an IFN-gamma activated site (GAS), -138 to -128 bp, and Spl site, -112 to -108 bp. Deletion of the 10 bp GAS sequence resulted in the complete loss of IFN-gamma induction of pCAM-175 promoter activity. TSH and forskolin action was also mapped between -175 bp and -97 bp from the start of translation. The mutant construct, pCAM-175delGAS mutl, which has no GAS sequence, exhibited no TSH-mediated suppression of promoter activity. We thus show that TSH/cAMP can downregulate ICAM-1 gene expression and inhibit the activity of cytokines (TNF-alpha and IFN-gamma) to increase ICAM-1 gene expression in FRTL-5 thyroid cells. We also localized elements on the 5'-flanking region of ICAM-1 important for these actions. We propose that this TSH/cyclic adenosine monophosphate (cAMP) action is a component of the mechanism to preserve self-tolerance of the thyroid during hormone-induced growth and function of the gland, and it may attenuate cytokine action during inflammatory reactions.

Syntaxin 1A and synaptotagmin I are key participants of fusion complex formation during exocytotic processes, and syntaxin 1A is known to be present in the plasma membrane. Here, we show the presence of not only synaptotagmin I but also syntaxin 1A in secretory granules of bovine adrenal chromaffin cells by immunogold electron microscopy, and further demonstrate the interaction of these proteins with chromogranins A and B (CGA and CGB), two major proteins of secretory granules. Interaction between chromogranins and the components of fusion complex also suggests active participation of CGA and CGB in fusion complex formation and subsequent exocytosis.

A cDNA, mSOD1, encoding cytosolic copper/zinc superoxide dismutase (CuZnSOD) was cloned and characterized from cell cultures of cassava (Manihot esculenta Crantz) which produce a high yield of SOD. mSOD1 encodes a 152-amino acid polypeptide with a pI value of 5.84. Southern analysis using an mSOD1-specific probe indicated that a single copy of the mSOD1 gene is present in the cassava genome. The mSOD1 gene is highly expressed in cultured cells, as well as in intact stems and tuberous roots. It is expressed at a low level in leaves and petioles. Transcripts of mSOD1 were not detected in nontuberous roots. Transcriptional level of mSOD1 reaches a high level at stationary phase, and then sharply decreases during further culture. In excised cassava leaves, the mSOD1 gene responded to various stresses in different ways. The stresses tested included changes in temperature and exposure to stress-inducing chemicals. Levels of mSOD1 transcript increased dramatically a few hours after heat stress at 37 degrees C and showed a synergistic effect with wounding stress. Levels decreased in response to chilling stress at 4 degrees C and showed an antagonistic effect with wounding stress. The gene was induced by abscisic acid, ethephon, NaCl, sucrose, and methyl viologen. These results indicate that the mSOD1 gene is involved in the response to oxidative stress induced by environmental change.