Effects of test item disclosure on medical licensing examination.

In 2012, the National Health Personnel Licensing Examination Board of Korea decided to publicly disclose all test items and answers to satisfy the test takers' right to know and enhance the transparency of tests administered by the government. This study investigated the effects of item disclosure on the medical licensing examination (MLE), examining test taker performance, psychometric characteristics, and factors affecting pass rates. This paper analyzed examinee performance data (n = 20,455) from 41 medical schools who took the MLE before (2009-2011) and after (2012-2014) the item disclosure policy (5548 total items). Changes in passing rates, performance of examinee, difficulty and reliability of the test, and factors affecting pass rate of the medical licensing examination before and after item disclosure were analyzed. In order to identify changes caused by item disclosure in the effects of student and school variables on the passing rate of MLE, Binary Logistic Hierarchical Linear Model was used. There was no significant change in pass rates before and after item disclosure. There was a modest increase in the proportion of test takers in the high-scoring group, following item disclosure. Degree completion status, gender, age of applicants and school mean were significant factors affecting pass rates, regardless of item disclosure. There was no difference between passing rates before and after item disclosure with respect to student- and school-level variables. Despite potential concerns for changes in test and examinee characteristics, empirical findings indicate that there was no significant difference caused by implementing item disclosure.

TIMP-1 modulates chemotaxis of human neural stem cells through CD63 and integrin signalling.

We recently reported that hNSCs (human neural stem cells) have the interesting characteristic of migration towards an intracranial glioma. However, the molecules and mechanisms responsible for tumour tropism are unclear. In the present study, we used microarray and proteomics analyses to identify a novel chemoattractant molecule, TIMP-1 (tissue inhibitor of metalloproteinase-1), secreted from human brain tumour tissues. We demonstrate that TIMP-1 significantly enhances hNSC adhesion and migration in a cell culture system. These effects were critically dependent on CD63, as shRNA-mediated ablation of CD63 expression attenuated the response. TIMP-1 significantly increased the number of FAs (focal adhesions) and cytoskeletal reorganization for cell migration in hNSCs, whereas knockdown of CD63 resulted in decreased hNSC spreading, FAs and migration, even after TIMP-1 treatment. In addition, TIMP-1 binding to CD63 activated ß1 integrin-mediated signalling through Akt and FAK phosphorylation, leading to pattern changes in distribution of vinculin and F-actin (filamentous actin). Furthermore, inactivation of ß1 integrin by use of a blocking antibody or inhibition of PI3K (phosphoinositide 3-kinase) signalling impaired the migration of hNSCs towards TIMP-1. Collectively, our results underline TIMP-1 as a novel and effective key regulator of CD63 and ß1 integrin-mediated signalling, which regulates hNSC adhesion and migration.

The effects of the Trendelenburg position and intrathoracic pressure on the subclavian cross-sectional area and distance from the subclavian vein to pleura in anesthetized patients.

BACKGROUND: The effects of maneuvers to increase intrathoracic pressure and of Trendelenburg position on the cross-sectional area (CSA) of the subclavian vein (SCV) and the relationship between the SCV and adjacent structures have not been investigated. METHODS: In ultrasonography-guided SCV catheterization (N = 30), the CSA of the SCV and the distance between the SCV and pleura (DSCV-pleura) were determined during 10-second airway opening, and 10-second positive inspiratory hold with 20 cm H2O in the supine position (S-0, and S-20) and the 10° Trendelenburg position (T-0, and T-20). In addition to a statistical significance of P < 0.05, CSA and DSCV-pleura differences of ≥15% were defined as clinically relevant changes. RESULTS: CSA (mean [95% confidence interval]) in S-20, T-0, and T-20 (1.02 [0.95-1.14] cm(2), 1.04 [0.95-1.15] cm(2), and 1.14 [1.04-1.24] cm(2), respectively) was significantly larger than a CSA in S-0 (0.93 [0.86-1.00] cm(2), all P < 0.001). However, only the increase of CSA in T-20 vs S-0 (0.21 cm(2), 23.2%) was clinically meaningful (≥15%). The number of patients who showed CSA increase ≥15% was more in S-0 to T-20 (57%) compared with those in S-0 to S-20 (23%) and S-0 to T-0 (27%). DSCV-pleura measurements (mean) in S-20 and T-20 (0.61 and 0.60 cm) were significantly shorter than those in S-0 (0.70 cm, all P < 0.001), but the reductions of DSCV-pleura were not clinically meaningful (≥15%). CONCLUSIONS: The combined application of inspiratory hold and Trendelenburg position provided a greater and more relevant degree of CSA increase without compromising DSCV-pleura, which may facilitate SCV catheterization. Further investigations are needed to determine whether these results affect the success rate of catheterization and the risk of procedural injury.

Transgenic mice expressing yellow fluorescent protein under control of the human tyrosine hydroxylase promoter.

Pathogenesis of Parkinson's disease and related catecholaminergic neurological disorders is closely associated with changes in the levels of tyrosine hydroxylase (TH). Therefore, investigation of the regulation of the TH gene system should assist in understanding the pathomechanisms involved in these neurological disorders. To identify regulatory domains that direct human TH expression in the central nervous system (CNS), we generated two transgenic mouse lines in which enhanced yellow fluorescent protein (EYFP) is expressed under the control of either 3.2-kb (hTHP-EYFP construct) human TH promoter or 3.2-kb promoter with 2-kb 3'-flanking regions (hTHP-ex3-EYFP construct) of the TH gene. In the adult transgenic mouse brain, the hTHP-EYFP construct directs neuron-specific EYFP expression in various CNS areas, such as olfactory bulb, striatum, interpeduncular nucleus, cerebral cortex, hippocampus, and particularly dentate gyrus. Although these EYFP-positive cells were identified as mature neurons, few EYFP-positive cells were TH-positive neurons. On the other hand, we could detect the EYFP mRNA expression in a subset of neurons in the olfactory bulb, midbrain, and cerebellum, in which expression of endogenous TH is enriched, with hTHP-ex3-EYFP transgenic mice. These results indicate that the 3.2-kb sequence upstream of the TH gene is not sufficient for proper expression and that the 2-kb sequence from the translation start site to exon 3 is necessary for expression of EYFP in a subset of catecholaminergic neurons.

Expression of tyrosine hydroxylase is epigenetically regulated in neural stem cells.

Tyrosine hydroxylase (TH) is the first and rate-limiting enzyme in the biosynthesis of catecholamines, and its expression is regulated in a developmental stage- and cell type-specific manner. Our previous work suggested that the genetic elements responsible for cell type-specific expression of TH were in the repressor region of the TH promoter between -2187 and -1232 bp. To investigate the molecular mechanisms underlying the specificity of TH expression, the DNA methylation patterns of the CpG islands in the repressor region of the TH promoter were examined in human neural stem cells (NSCs) and dopaminergic neuron-like cells. Using a bisulfite sequencing method, we found that the cytosine residues of CpG islands within the NRSE-R site were specifically methylated in NSCs, but not in SH-SY5Y neuroblastoma cells. In NSCs, CpG methylation correlated with reduced TH gene expression, and inhibition of DNA methylation with 5-azacytidine restored TH expression. Furthermore, methyl-CpG binding domain proteins (MBDs) bound to the highly methylated X-1 and X-2 regions of the TH gene in NSCs. Taken together, these results suggest that region-specific methylation and MBDs play important roles in TH gene regulation in NSCs.

Genome-Wide Analysis Identifies NURR1-Controlled Network of New Synapse Formation and Cell Cycle Arrest in Human Neural Stem Cells.

Nuclear receptor-related 1 (Nurr1) protein has been identified as an obligatory transcription factor in midbrain dopaminergic neurogenesis, but the global set of human NURR1 target genes remains unexplored. Here, we identified direct gene targets of NURR1 by analyzing genome-wide differential expression of NURR1 together with NURR1 consensus sites in three human neural stem cell (hNSC) lines. Microarray data were validated by quantitative PCR in hNSCs and mouse embryonic brains and through comparison to published human data, including genome-wide association study hits and the BioGPS gene expression atlas. Our analysis identified ~40 NURR1 direct target genes, many of them involved in essential protein modules such as synapse formation, neuronal cell migration during brain development, and cell cycle progression and DNA replication. Specifically, expression of genes related to synapse formation and neuronal cell migration correlated tightly with NURR1 expression, whereas cell cycle progression correlated negatively with it, precisely recapitulating midbrain dopaminergic development. Overall, this systematic examination of NURR1-controlled regulatory networks provides important insights into this protein's biological functions in dopamine-based neurogenesis.

Migration of human neural stem cells toward an intracranial glioma.

Many in vivo and in vitro studies have demonstrated the targeted migration of neural stem cells (NSC) to infiltrating brain tumors, including malignant glioma, highlighting a potential therapeutic approach. However, there is not enough information to apply this approach to clinical therapy. The most important things in stem cell therapy for brain tumors involve selecting the appropriate neural progenitor type and optimizing the efficiency of the cell engraftment. By histological analysis using two different live-dyes, human NSCs were shown to migrate away from the transplanted site in the direction of the expanding C6 glioma and to intermix with the tumor bed, especially with the tumor core. This intermixing occurred within 7 days when NSCs were implanted into glioma model. The time course of migratory HB1.F5 with the greatest mobility of three NSC lines was as follows. As early as 3 days after transplantation, several NSCs were found leaving the implant site, primarily approaching microsatellites and frontier cells located near the site of NSC implantation. Through 7 days post-transplantation, massive numbers of NSCs continued to be attracted to and interspersed with C6 glioma, and were finally distributed extensively throughout the whole tumor bed, including the core and penumbra of the tumor mass. However, NSCs appeared to penetrate into the tumor mass very well, whereas normal fibroblast cells could not migrate. These findings strengthen the potential for human NSCs as attractive vehicles to improve therapeutic gene delivery to cancer or glioma if they are optimized to selectively kill neoplastic cells.

Decreased serotonin2C receptor responses in male patients with schizophrenia.

Serotonin (5-HT)2C receptors in brain affect psychosis, reward, substance abuse, anxiety, other behaviors, appetite, body temperature, and other physiological measures. They also have been implicated in antipsychotic drug efficacy and side effects. We previously reported that the hyperthermia following administration of MK-212, a predominantly 5-HT(2C) receptor agonist, was diminished in a small sample of patients with schizophrenia (SCH), suggesting decreased 5-HT(2C) receptor responsiveness. We have now studied the responses to oral MK-212 and placebo in a larger sample of unmedicated male SCH (n = 69) and normal controls (CON) (n = 33), and assessed the influence of comorbid substance abuse (SA) on oral body temperature, behavioral responses, etc. The placebo-adjusted oral body temperature response to MK-212 was significantly lower in SCH compared to CON and not significantly different between the SCH with or without SA. Some behavioral responses to MK-212, e.g. self-rated feelings of increased anxiety, depression and decreased calmness, or good overall feeling, were significantly lower in the SCH patients compared to CON. These results add to the evidence for diminished 5-HT(2C) receptor responsiveness in SCH patients compared to CON and are consistent with reported association of HTR(2C) polymorphisms, leading to decreased expression or function of the HTR(2C) in patients with SCH.

Intracellular trafficking and metabolic turnover of yeast prepro-alpha-factor-SRIF precursors in GH3 cells.

Chimeric genes coding for prepro region of yeast alpha-factor and anglerfish SRIF were expressed in rat GH3 cells to determine whether yeast signals could regulate hormone processing in mammalian cells. We report that nascent hybrid polypeptides were efficiently targeted to ER, where cleavage of signal peptides and core glycosylation occurred, and were localized mainly in Golgi. These data indicate that prepro region of yeast alpha-factor functions in sorting molecules to secretory pathway in mammalian cells. A hybrid construct with a mutated signal peptide underwent similar ER translocation, whereas such a mutation resulted in defective translocation in yeast (Cheong et al., 1997). This difference may be due to the differences in ER translocation between yeast and mammalian cells, i.e., posttranslational versus cotranslational translocation. Processing and secretion of metabolically labeled hybrid propeptides to mature SRIF peptides were assessed by HPLC. When pulse-labeled cells were chased for up to 2 h, intracellular propeptides disappeared with a half-life of approximately 25 min, showing that approximately 68% of initially synthesized propeptides were secreted constitutively. About 22% of SRIF-related products were proteolytically processed to mature SRIF, of which 38.7% were stored intracellularly with a half-life of approximately 2 h. In addition, immunocytochemical localization showed that a small proportion of SRIF molecules accumulated in secretory vesicles. All these results suggest that yeast prepropeptide could direct hybrid precursors to translocate into ER lumen and transit through secretory pathway to the distal elements of Golgi compartment, but could process and target it less efficiently to downstream in rat endocrine cells.

Overexpression of midbrain-specific transcription factor Nurr1 modifies susceptibility of mouse neural stem cells to neurotoxins.

Nurr1 is a member of the nuclear receptor superfamily of transcription factors that is highly expressed in midbrain dopaminergic (DA) neurons, the cells primarily lost in human Parkinson's disease (PD), and in Nurr1-null mice selective agenesis of midbrain DA neurons is found. To investigate possible correlation between the expression of Nurr1 gene and neurotoxin-induced cell death of DA neurons, a neural stem cell line (NSC, A3) and Nurr1-overexpressing NSC (A3.Nurr1) were exposed to DA neurotoxins 6-hydroxydopamine (6-OHDA) and methyl phenylpyridinium (MPP(+)). Although both neurotoxins were shown to induce cell death in A3 and A3.Nurr1 cells, patterns of cell deaths were different. A3.Nurr1 cells showed increased vulnerability to 6-OHDA cytotoxicity, but increased resistance to MPP(+)-induced cell death when compared to A3 cells. To investigate the differential vulnerability to neurotoxins by Nurr1 protein correlates with biochemical features that discriminate between apoptosis and necrosis, we carried out a nucleosomal DNA fragmentation assay and electron microscopy. While 6-OHDA treatment induced shrinkage of cytoplasmic membrane, condensation of nuclei and generation of apoptotic bodies in both cell lines, cells treated with MPP(+) showed mitochondrial swelling, indicating that 6-OHDA- but not MPP(+)-mediated cell death was apoptotic. These results suggest that DA neuronal cell death in response to 6-OHDA and MPP(+) may progress through separate signaling pathways differentially regulated by the Nurr1 protein. Our observations indicated that Nurr1 may play a role in the manifestation of DA neurotoxicity and that variations in Nurr1 expression might be a susceptibility factor for DA neurodegeneration in PD.

Nurr1 represses tyrosine hydroxylase expression via SIRT1 in human neural stem cells.

Nurr1 is an orphan nuclear receptor best known for its essential role in the development and maintenance of midbrain dopaminergic (DA) neurons. During DA neurogenesis, Nurr1 directly targets human tyrosine hydroxylase (hTH). Here we investigated this targeting to identify the molecular mechanisms by which Nurr1 regulates DA neurogenesis. We previously cloned the hTH promoter and found three consensus elements for Nurr1 binding: NBRE-A, -B, and -C. In the present study, gel retardation and luciferase assays using hTH constructs showed that Nurr1 preferentially bound to NBRE-A, through which it mediated transcriptional activity. Furthermore, Nurr1 displayed dual-function transcriptional activities depending on the cell type. In DA-like SH-SY5Y cells, Nurr1 dose-dependently stimulated hTH-3174 promoter activity by 7- to 11-fold. However, in the human neural stem cell (hNSC) line HB1.F3, Nurr1 strongly repressed transcription from the same promoter. This repression was relieved by mutation of only the NBRE-A element and by nicotinamide [an inhibitor of class III histone deacetylases (HDACs), such as SIRT1], but not by trichostatin A (an inhibitor of class I and II HDACs). SIRT1 was strongly expressed in the nucleus of HB1.F3 cells, while it was localized in the cytoplasm in SH-SY5Y cells. ChIP assays of HB1.F3 cells showed that Nurr1 overexpression significantly increased the SIRT1 occupancy of the NBRE-A hTH promoter region, while low SIRT1 levels were observed in control cells. In contrast, no significant SIRT1 recruitment was observed in SH-SY5Y cells. These results indicate that differential SIRT1 localization may be involved in hTH gene regulation. Overall, our findings suggest that Nurr1 exists in dual transcriptional complexes, including co-repressor complexes that can be remodeled to become co-activators and can fine-tune hTH gene transcription during human DA neurogenesis.

Integrative analysis of congenital muscular torticollis: from gene expression to clinical significance.

BACKGROUND: Congenital muscular torticollis (CMT) is characterized by thickening and/or tightness of the unilateral sternocleidomastoid muscle (SCM), ending up with torticollis. Our aim was to identify differentially expressed genes (DEGs) and novel protein interaction network modules of CMT, and to discover the relationship between gene expressions and clinical severity of CMT. RESULTS: Twenty-eight sternocleidomastoid muscles (SCMs) from 23 subjects with CMT and 5 SCMs without CMT were allocated for microarray, MRI, or immunohistochemical studies. We first identified 269 genes as the DEGs in CMT. Gene ontology enrichment analysis revealed that the main function of the DEGs is for extracellular region part during developmental processes. Five CMT-related protein network modules were identified, which showed that the important pathway is fibrosis related with collagen and elastin fibrillogenesis with an evidence of DNA repair mechanism. Interestingly, the expression levels of the 8 DEGs called CMT signature genes whose mRNA expression was double-confirmed by quantitative real time PCR showed good correlation with the severity of CMT which was measured with the pre-operational MRI images (R2 ranging from 0.82 to 0.21). Moreover, the protein expressions of ELN, ASPN and CHD3 which were identified from the CMT-related protein network modules demonstrated the differential expression between the CMT and normal SCM. CONCLUSIONS: We here provided an integrative analysis of CMT from gene expression to clinical significance, which showed good correlation with clinical severity of CMT. Furthermore, the CMT-related protein network modules were identified, which provided more in-depth understanding of pathophysiology of CMT.

Spectral entropy for assessing the depth of propofol sedation.

BACKGROUND: For patients in the intensive care unit (ICU) or under monitored anesthetic care (MAC), the precise monitoring of sedation depth facilitates the optimization of dosage and prevents adverse complications from underor over-sedation. For this purpose, conventional subjective sedation scales, such as the Observer's Assessment of Alertness/Sedation (OAA/S) or the Ramsay scale, have been widely utilized. Current procedures frequently disturb the patient's comfort and compromise the already well-established sedation. Therefore, reliable objective sedation scales that do not cause disturbances would be beneficial. We aimed to determine whether spectral entropy can be used as a sedation monitor as well as determine its ability to discriminate all levels of propofol-induced sedation during gradual increments of propofol dosage. METHODS: In 25 healthy volunteers undergoing general anesthesia, the values of response entropy (RE) and state entropy (SE) corresponding to each OAA/S (5 to 1) were determined. The scores were then analyzed during each 0.5 mcg/ml- incremental increase of a propofol dose. RESULTS: We observed a reduction of both RE and SE values that correlated with the OAA/S (correlation coefficient of 0.819 in RE-OAA/S and 0.753 in SE-OAA/S). The RE and SE values corresponding to awake (OAA/S score 5), light sedation (OAA/S 3-4) and deep sedation (OAA/S 1-2) displayed differences (P < 0.05). CONCLUSIONS: The results indicate that spectral entropy can be utilized as a reliable objective monitor to determine the depth of propofol-induced sedation.

Identification of gliotropic factors that induce human stem cell migration to malignant tumor.

Neural stem cells are mobile, are attracted to regions of brain damage, and can migrate a considerable distance to reach a glioma site. However, the molecular basis of the progression of gliotropism to malignant gliomas remains poorly understood. With the use of clinically and histologically assessed glioma cells, we have assessed their protein and gene profiles via proteomics and microarray approaches, and have identified candidate genes from human glioma tissues. This research is expected to provide clues to the molecular mechanisms underlying the migration of neural stem cells (F3 cell) to glioma sites. The expression of 16 proteins was shown to have increased commonly in human glioma tissues. Among them, the expression of annexin A2, TIMP-1, COL11A1, bax, CD74, TNFSF8, and SPTLC2 were all increased in human glioma cells, as confirmed by Western blotting and immunohistochemical staining. In particular, annexin A2 effects an increase in migration toward F3 and glioblastoma cells (U87 cell) in a Boyden chamber migration assay. An ERK inhibitor (PD98057) and a CDK5 inhibitor (rescovitine) inhibited 50% and 90% of annexin A2-induced migration in F3 cells, respectively. A similar chemotactic migration was noted in F3 and U87 cells. These results demonstrated that 7 candidate proteins may harbor a potential glioma tropism factor relevant to the pathology of malignant glioma. These results reveal that this novel molecular approach to the monitoring of glioma may provide clinically relevant information regarding tumor malignancy, and should also prove appropriate for high-throughput clinical screening applications.

Meningitis after a combined spinal epidural anesthesia: A case report.

The incidence of post-dural puncture meningitis is very low. A 44-year-old patient developed a fever (38degrees C, headache, neck stiffness, nausea, and vomiting after combined spinal epidural (CSE) anesthesia and surgery for closed reduction and internal fixation (CRIF) with intramedullary (IM) nailing, tibia, Rt. With a preliminary diagnosis of bacterial meningitis, empiric broad spectrum antimicrobial treatment was immediately started after cerebrospinal fluid (CSF) sampling. The CSF was clear and revealed a white blood cell count, protein, glucose, and pressure of 146/micrometer, 225 mg/dl, 48 mg/dl (serum 151 mg/dl), and 26 cmH2O, respectively. The CSF stain and culture were negative. Considering the injection of preventive antibiotics before CSE anesthesia, partially treated bacterial meningitis was suspected. Four weeks later, clinical symptoms had improved before the patient was discharged.

Regulation of human tyrosine hydroxylase gene by neuron-restrictive silencer factor.

Tyrosine hydroxylase (TH), the biosynthetic enzyme of catecholamine, is synthesized specifically in catecholaminergic neurons. Thus, it is possible that neuronal cell type-specific expression of this gene is coordinately regulated. One of the neuron-specific transcription regulators, neuron-restrictive silencer factor (NRSF)/repressor element 1 (RE1) silencing transcription factor (REST), represses the expression of neuronal genes in non-neuronal cells. To elucidate the molecular mechanisms that control catecholaminergic neuronal expression of human TH, we initially characterized the 5' regulatory region. Previous studies have shown that a 3174 bp fragment of the human TH promoter confers specific expression to the reporter gene in dopaminergic neuron-like cell lines. Within this 5' regulatory region, three putative neuron-restrictive silencer elements (NRSE)/RE1 were identified, which bound NRSF/REST in a sequence-specific manner, as confirmed using EMSA and ChIP assays. In transient transfection assays, deletion or mutation of NRSE/RE1 elements led to a 7-fold increase in activity of the 3.2 kb TH promoter in human neural stem cells (NSCs), but had no major effects on differentiated neuron-like cells. Suppression of NRSF/REST functions with either the histone deacetylase inhibitor, trichostatin, or DN-NRSF induced TH promoter activity. Our data strongly suggest that NRSF/REST functions as a repressor of TH transcription in NSCs via a mechanism dependent on the TH NRSE/RE1 sites.

Thrombin induces suppressor of cytokine signaling 3 expression in brain microglia via protein kinase Cdelta activation.

Microglia (brain macrophages) are activated upon brain damage. In this study, we demonstrated that thrombin, a pro-inflammatory stimulator of microglia, induced expression of suppressors of cytokine signaling (SOCS) in microglia. RT-PCR analysis and Northern blot analysis showed that thrombin induced SOCS3 mRNA expression. Further experiments indicated SOCS3 expression was not affected by cycloheximide, indicating thrombin directly stimulated SOCS3 transcript expression without de novo protein synthesis. We investigated whether PKCdelta played a role in thrombin-stimulated SOCS3 expression. We found that thrombin activated PKCdelta, and the specific inhibitor of PKCdelta, rottlerin, significantly suppressed thrombin-stimulated SOCS3 expression. In thrombin-pretreated cells, microglial activation-induced by another inflammatory stimulator, lipopolysaccharide, was attenuated compared to that in non-pretreated cells. These results suggest thrombin induce not only proinflammatory mediators but also negative feedback regulators of inflammation, SOCS, which prevent prolonged inflammatory reactions in microglia.

Evidence of a novel dipeptidyl aminopeptidase in mammalian GH(3) cells: new insights into the processing of peptide hormone precursors.

We investigated whether yeast signals could regulate hormone processing in mammalian cells. Chmeric genes coding for the prepro region of yeast alpha-factor and the functional hormone region of anglerfish somatostatin was expressed in rat pituitary GH(3) cells. The nascent prepro-alpha-factor-somatostatin peptides disappeared from cells with a half-life of 30 min, and about 20% of unprocessed precursors remained intracellular after a 2 h chase period. Disappearance of propeptide was insensitive to lysosomotropic agents, but was inhibited at 15 degrees C or 20 degrees C, suggesting that the hybrid propeptides were not degraded in the secretory pathway to the trans Golgi network or in lysosomes. It appeared that while most unprocessed precursors were constitutively secreted into the medium, a small portion were processed at their paired dibasic sites by prohormone-processing enzymes located in trans Golgi network/secretory vesicles, resulting in the production of mature somatostatin peptides. To test this hypothesis, we investigated the processing pattern of two different hybrid precursors: the 52-1 hybrid precursor, which has a Glu-Ala spacer between the prepro region of alpha-factor and somatostatin, and the 58-1 hybrid precursor, which lacks the Glu-Ala spacer. Processing of metabolically labeled hybrid propeptides to smaller somatostatin peptides was assessed by HPLC. When pulse-labeled cells were chased for up to 2 h, 68% of the initially synthesized propeptides were secreted constitutively. About 22% of somatostatin-related products were proteolytically processed to mature somatostatin, of which 38.7% were detected intracellularly after 2 h. From N-terminal peptide sequence determination of somatostatin-related products in GH(3)-52 and GH(3)-58 cells, we found that both hybrid precursors were accurately cleaved at their dibasic amino acid sites. Notably, we also observed that the Glu-Ala spacer sequence was removed from 52-1 hybrid precursors. The latter result strongly suggests that a novel dipeptidyl aminopeptidase activity - a yeast STE13-like enzyme - is present in the post-trans Golgi network compartment of GH(3) cells. The data from these studies indicate that mechanisms which control protein secretion are conserved between yeast and mammalian cells.

Sonic hedgehog and FGF8 collaborate to induce dopaminergic phenotypes in the Nurr1-overexpressing neural stem cell.

Neural stem cells are self-renewing cells capable of differentiating into all neural lineage cells in vivo and in vitro. In the present study, coordinated induction of midbrain dopaminergic phenotypes in an immortalized multipotent neural stem cell line can be achieved by both overexpression of nuclear receptor Nurr1, and fibroblast growth factor-8 (FGF-8), and sonic hedgehog (Shh) signals. Nurr1 overexpression induces neuronal differentiation and confers competence to respond to extrinsic signals such as Shh and FGF-8 that induce dopaminergic fate in a mouse neural stem cell line. Our findings suggest that immortalized NSCs can serve as an excellent model for understanding mechanisms that regulate specification of ventral midbrain DA neurons and as an unlimited source of DA progenitors for treating Parkinson disease patients by cell replacement.