Down modulation of N-myc, heat-shock protein 70, and nucleolin during the differentiation of human neuroblastoma cells

Extracellular elevation of adrenomedullin, a gene associated with schizophrenia, suppresses heat shock protein 1A/1B mRNA

Several recent gene expression studies on schizophrenia, including one using monozygotic twins discordant for the disease, have reported the upregulation of adrenomedullin (ADM), which was initially identified as a vasodilator hormone. It has been hypothesized that upregulation of ADM may be a susceptibility factor for schizophrenia, although the exact role of ADM in the central nervous system remains unclear. In this study, we used a microarray analysis to investigate the changes in global gene expression induced by the administration of exogenous ADM in SK-N-SH cells, which allowed us to evaluate the effects of elevated ADM on the central nervous system. A quantitative reverse-transcription PCR study showed that the levels of HSPA1A/1B mRNA, another gene that has been associated with schizophrenia, were significantly suppressed after exogenous ADM treatment. These results indicate that elevated ADM may be involved in the etiology of schizophrenia through the regulation of heat shock protein signaling.

Chaperones in cell cycle regulation and mitogenic signal transduction: a review

Chaperones/heat shock proteins (HSPs) of the HSP90 and HSP70 families show elevated levels in proliferating mammalian cells and a cell cycle-dependent expression. They transiently associate with key molecules of the cell cycle control system such as Cdk4, Wee-1, pRb, p53, p27/Kip1 and are involved in the nuclear localization of regulatory proteins. They also associate with viral oncoproteins such as SV40 super T, large T and small t antigen, polyoma large and middle S antigen and EpsteinBarr virus nuclear antigen. This association is based on a J-domain in the viral proteins and may assist their targeting to the pRb/E2F complex. Small HSPs and their state of phosphorylation and oligomerization also seem to be involved in proliferation and differentiation. Chaperones/HSPs thus play important roles within cell cycle processes. Their exact functioning, however, is still a matter of discussion. HSP90 in particular, but also HSP70 and other chaperones associate with proteins of the mitogen-activated signal cascade, particularly with the Src kinase, with tyrosine receptor kinases, with Raf and the MAP-kinase activating kinase (MEK). This apparently serves the folding and translocation of these proteins, but possibly also the formation of large immobilized complexes of signal transducing molecules (scaffolding function).

HOXC6 and HOXC11 increase transcription of S100beta gene in BrdU-induced in vitro differentiation of GOTO neuroblastoma cells into Schwannian cells

HOX genes encode transcription factors that play a key role in morphogenesis and cell differentiation during embryogenesis of animals. Human neuroblastoma cells are known to be chemically induced to differentiate into neuronal or Schwannian cells. In the present study, we investigated the roles of HOX genes in differentiation of GOTO neuroblastoma cells into Schwannian cells. When GOTO cells were grown in the presence of 5-bromo-2'-deoxyuridine (BrdU), they increased the expressions of two HOX genes (HOXC6 and HOXC11) and marker genes for Schwannian cells (S100beta and myelin basic protein). Forced expression of HOXC11 alone or both HOXC6 isoform 1 and HOXC11 induced the expression of S100beta in GOTO cells. In transient transfection experiments, the overexpression of HOXC6 and HOXC11 transactivated the S100beta promoter-reporter construct. Taken together, our results suggest that HOXC6 and HOXC11 are associated with differentiation of GOTO cells into Schwannian cells through the transcriptional activation of S100beta gene.

Involvement of nPKC-MAPK pathway in the decrease of nucleophosmin/B23 during megakaryocytic differentiation of human myelogenous leukemia K562 cells

Human myelogenous leukemia K562 cells were induced to undergo megakaryocytic differentiation by long-term treatment with phorbol ester 12-O-tetradecanoyl-phorbol-13-acetate (TPA). The protein level of nucleophosmin/B23 (NPM/B23), a nucleolar protein, was substantially decreased upon TPA treatment. In this study, we found that the proteasome inhibitors blocked the decrease of NPM/B23 protein in response to TPA, suggesting the proteasomes were involved in the downregulation of NPM/B23 upon megakaryocytic differentiation. To investigate the signaling pathway in the downregulation of NPM/B23 during early TPA-induced megakaryocytic differentiation of K562 cells, K562 cells were treated with TPA in the presence of the PKC isozyme-selective inhibitors, GF109203X and Gö 6976, or MEK1 inhibitor, PD98059. The decrease of NPM/B23 protein in the TPA-treated K562 cells was blocked by GF109203X but not by Gö 6976, suggesting the involvement of novel PKCs in the downregulation of NPM/B23 during TPA-induced megakaryocytic differentiation of K562 cells. The application of MEK1 inhibitor PD98059 upon TPA treatment blocked the TPA-induced decrease of NPM/B23 protein and aborted the megakaryocytic differentiation but not to break through the cell growth arrest. Unlike NPM/B23, the degradation of nucleolin in the TPA-treated K562 cells could not be blocked by PD98059 while the TPA-induced megakaryocytic differentiation was abrogated. The decrease of NPM/B23 protein seems to be more correlated with the novel PKC-MAPK-induced megakaryocytic differentiation than another nucleolar protein, nucleolin. Taken together, our results indicated that novel PKC-MAPK pathway was required for the decrease of NPM/B23 during TPA-induced megakaryocytic differentiation.

Integrated proteomic and transcriptomic profiling of mouse lung development and Nmyc target genes

Although microarray analysis has provided information regarding the dynamics of gene expression during development of the mouse lung, no extensive correlations have been made to the levels of corresponding protein products. Here, we present a global survey of protein expression during mouse lung organogenesis from embryonic day E13.5 until adulthood using gel-free two-dimensional liquid chromatography coupled to shotgun tandem mass spectrometry (MudPIT). Mathematical modeling of the proteomic profiles with parallel DNA microarray data identified large groups of gene products with statistically significant correlation or divergence in coregulation of protein and transcript levels during lung development. We also present an integrative analysis of mRNA and protein expression in Nmyc loss- and gain-of-function mutants. This revealed a set of 90 positively and negatively regulated putative target genes. These targets are evidence that Nmyc is a regulator of genes involved in mRNA processing and a repressor of the imprinted gene Igf2r in the developing lung.

Neural Differentiation of Human Neuroblastoma GOTO Cells via a Rho-Rho Kinase-Phosphorylation Signal Transduction and Continuous Observation of a Single GOTO Cell during Differentiation

Nerve growth factor, retinoic acid, dibutyryl cAMP, ganglioside G(Q1b), and botulinum C3 exoenzyme were evaluated for their neural differentiating potential on human neuroblastoma GOTO cells. C3 exoenzyme is an ADP-ribosyltransferase inactivating Rho protein (a small GTP-binding protein). C3 exoenzyme caused the fastest differentiation of GOTO cells into neural cells and induced the strongest network of the cells. Fasudil, an inhibitor of Rho-kinase, induced outgrowth of the neurites in the GOTO cells. Calyculin A, an inhibitor of phosphatases including myosin phosphatase, counteracted C3 exoenzyme-induced neurite outgrowth of the cells. These findings suggest that differentiation of GOTO cells triggered by C3 exoenzyme is attained via inactivation of Rho protein, inhibition of Rho-kinase, and activation of myosin phosphatase. Because of the strong differentiating potential of C3 exoenzyme, the transduction pathway consisting of Rho protein, Rho-kinase, and myosin phosphatase seems to be main stream in the neural differentiation of GOTO cells. A single GOTO cell was observed continuously after treatment with C3 exoenzyme. The cell started to change shape from its original morphology only 15 min after treatment with C3 exoenzyme, and it was completely spherical within 60 min. Neurites appeared on the membrane of the cell 2 hr after the treatment and then gradual outgrowth began. These observations are fundamental information in elucidating the mechanism of neural differentiation, especially at an early stage.

Immunodetection of human telomerase reverse-transcriptase (hTERT) re-appraised: nucleolin and telomerase cross paths

The involvement of telomerase in cellular immortalization and senescence has often been assessed by means of telomerase expression at the RNA level and quantification of telomerase activity by the telomeric repeat amplification protocol assay. However, these methods either neglected the existence of various telomerase splice variants, or ignored the nonconventional functions of telomerase independent of its ability to elongate and maintain telomere length. Immunodetection of telomerase is now being recognized as a necessary approach to precisely elucidate its roles in oncogenesis and senescence. A few antibodies directed against the catalytic subunit of the human telomerase (hTERT) are currently used but their specificity is not always demonstrated. A survey of the literature showed inconsistencies and led us to comparatively re-evaluate the most frequently used antibodies. Surprisingly, mass spectrometry, two-dimensional gel analysis and immunofluorescent experiments revealed that the most frequently used hTERT immunoprobe, a mouse monoclonal antibody that was claimed to be directed against an hTERT protein epitope, in fact recognizes nucleolin rather than telomerase. Our findings have interesting implications regarding the biology of nucleolin and telomerase in the context of pathophysiological investigations recently carried out.

A multifunctional shuttling protein nucleolin is a macrophage receptor for apoptotic cells

Early apoptotic Jurkat T cells undergo capping of CD43, and its polylactosaminyl saccharide chains serve as ligands for phagocytosis by macrophages. This suggests the presence of a polylactosaminoglycan-binding receptor on macrophages. Here we show that this receptor is nucleolin, a multifunctional shuttling protein present in nucleus, cytoplasm, and on the surface of some types of cells. Nucleolin was detected at the surface of macrophages, and anti-nucleolin antibody inhibited the binding of the early apoptotic cells to macrophages. Nucleolin-transfected HEK293 cells expressed nucleolin on the cell surface and bound the early apoptotic cells but not phosphatidylserine-exposing late apoptotic cells. This binding was inhibited by anti-nucleolin antibody, by polylactosamine-containing oligosaccharides, and by anti-CD43 antibody. Deletion of the antibody binding region of nucleolin resulted in loss of the apoptotic cell-binding ability. Moreover, truncated recombinant nucleolin in solution containing this region blocked the apoptotic cell binding to macrophages, and the blocking effect was cancelled by the oligosaccharides. These results indicate that nucleolin is a macrophage receptor for apoptotic cells.

Nutrients as trophic factors in neurons and the central nervous system: role of retinoic acid

In multicellular organisms, death, survival, proliferation, and differentiation of a given cell depend on signals produced by neighboring and/or distant cells, resulting in the coordinated development and function of the various tissues. In the nervous system, control of cell survival and differentiation is achieved through the action of a distinct group of polypeptides collectively known as neurotrophic factors. Recent findings support the view that trophic factors also are involved in the response of the nervous system to acute injury. By contrast, nutrients are not traditionally viewed as potential trophic factors; however, there is increasing evidence that at least some influence neuronal differentiation. During development the brain is responsive to variations in nutrient supply, and this increased sensitivity or vulnerability of the brain to nutrient supply may reappear during neuronal repair, a period during which a rapid membrane resynthesis and reestablishment of synthetic pathways occur. To further evaluate the potential of specific nutrients to act as pharmacologic agents in the repair of injured neurons, the effects of retinoic acid, an active metabolite of vitamin A, and its role as a trophic factor are discussed. This literature review is intended to provide background information regarding the effect of retinoic acid on the cholinergic phenotype and the differentiation of these neurons and to explain how it may promote neuronal repair and survival following injury.

Up-regulation of nucleolin mRNA and protein in peripheral blood mononuclear cells by extracellular-regulated kinase

The signal transduction pathways regulating nucleolin mRNA and protein production have yet to be elucidated. Peripheral blood mononuclear cells treated with phorbol 12-myristate 13-acetate showed steady state levels of nucleolin mRNA that were 2-2.5-fold greater than untreated control cells. The up-regulation of nucleolin mRNA was substantially repressed by U0126, a specific inhibitor that blocks phosphorylation of extracellular-regulated kinase (ERK). Calcium ionophores and ionomycin also activated ERK and substantially elevated nucleolin mRNA levels, demonstrating phorbol 12-myristate 13-acetate and calcium signaling converge on ERK. Drugs that affected protein kinase C, protein kinase A, and phospholipase C signal transduction pathways did not alter nucleolin mRNA levels significantly. The half-life of nucleolin mRNA increased from 1.8 h in resting cells to 3.2 h with phorbol ester activation, suggesting ERK-mediated posttranscriptional regulation. Concomitantly, full-length nucleolin protein was increased. The higher levels of nucleolin protein were accompanied by increased binding of a 70-kDa nucleolin fragment to the 29-base instability element in the 3'-untranslated region of amyloid precursor protein (APP) mRNA in gel mobility shift assays. Supplementation of rabbit reticulocyte lysate with nucleolin decreased APP mRNA stability and protein production. These data suggest ERK up-regulates nucleolin posttranscriptionally thereby controlling APP production.

Myc induces the nucleolin and BN51 genes: possible implications in ribosome biogenesis

The c-Myc oncoprotein and its dimerization partner Max bind the DNA core consensus sequence CACGTG (E-box) and activate gene transcription. However, the low levels of induction have hindered the identification of novel Myc target genes by differential screening techniques. Here, we describe a computer-based pre-selection of candidate Myc/Max target genes, based on two restrictive criteria: an extended E-box consensus sequence for Myc/Max binding and the occurrence of this sequence within a potential genomic CpG island. Candidate genes selected by these criteria were evaluated experimentally for their response to Myc. Two Myc target genes are characterized here in detail. These encode nucleolin, an abundant nucleolar protein, and BN51, a co-factor of RNA polymerase III. Myc activates transcription of both genes via E-boxes located in their first introns, as seen for several well-characterized Myc targets. For both genes, mutation of the E-boxes abolishes transcriptional activation by Myc as well as repression by Mad1. In addition, the BN51 promoter is selectively activated by Myc and not by USF, another E-box-binding factor. Both nucleolin and BN51 are implicated in the maturation of ribosomal RNAs, albeit in different ways. We propose that Myc, via regulation of these and probably many other transcriptional targets, may be an important regulator of ribosome biogenesis.

Different constitutive heat shock protein 70 expression during proliferation and differentiation of rat C6 glioma cells

Analysis of constitutive heat shock protein 70 (HSC70) concentration in unstressed proliferating and differentiated rat C6 glioma cells revealed a striking reduction in the amount of HSC70 in differentiated cells. Proliferating cells showed a significantly higher HSC70 concentration, particularly observable during S phase in synchronous cultures. The activity of the cAMP/PKA signaling pathway was enhanced in differentiated cells. cAMP-elevating treatments both inhibited growth and reduced HSC70 concentration. Inactivation of PKA by H-89 upregulated the reduced HSC70 expression in differentiated cells and stimulated proliferation. Treatment with an inhibitor of MAP kinase activation (PD98059) reduced the HSC70 concentration. We assume that cAMP does not directly inhibit HSC70 expression by transcriptional repression, but by its inhibitory effect on the MAP kinase pathway.

Attenuated c-fos mRNA induction after middle cerebral artery occlusion in CREB knockout mice does not modulate focal ischemic injury

To elucidate the mechanism of ischemia-induced signal transduction in vivo, we investigated the effect of the targeted disruption of the alpha and delta isoforms of the cAMP-responsive element-binding protein (CREB) on c-fos and heatshock protein (hsp) 72 gene induction. Permanent focal ischemia was induced by occlusion of the middle cerebral artery of the CREB mutant mice (CREB(-/-), n = 5) and the wild-type mice (n = 6). Three hours after onset of ischemia, the neurologic score was assessed and pictorial measurements of ATP and cerebral protein synthesis (CPS) were carried out to differentiate between the ischemic core (where ATP is depleted), the ischemic penumbra (where ATP is preserved but CPS is inhibited), and the intact tissue (where both ATP and CPS are preserved). There were no significant differences in neurologic score or in ATP, pH, and CPS between the two groups, suggesting that the sensitivity of both strains to ischemia is the same. Targeted disruption of the CREB gene significantly attenuated c-fos gene induction in the periischemic ipsilateral hemisphere but had no effect on either c-fos or hsp72 mRNA expression in the penumbra. The observations demonstrate that CREB expression, despite its differential effect on c-fos, does not modulate acute focal ischemic injury.

Exposure of embryonic cells to alcohol: contrasting effects during preimplantation and postimplantation development

Alcohol is a known teratogen that causes a broad variety of developmental anomalies, including fetal growth retardation, craniofacial anomalies, and neurological disorders. The etiology of this multiple defect syndrome, known as fetal alcohol syndrome, has been studied in animal models that reproduce many of the attributes of the human disease. These studies show that ethanol is most teratogenic during organogenesis and development of the nervous system. The molecular basis of fetal alcohol effects has been further investigated using embryo and cell culture systems. Recent studies show that signal transduction pathways controlling cell proliferation are perturbed during ethanol exposure. Ethanol can induce the release of intracellular calcium stores, which stimulates the cell cycle, and it also up-regulates the expression of myc proteins associated with cell proliferation. Increased proliferation is advantageous during the preimplantation period, but ethanol interference with terminal differentiation events within developing tissues during organogenesis may underlie alcohol teratogenicity.

Effects of dibutyryl cAMP and bromodeoxyuridine on expression of N-acetylglucosaminyltransferases III and V in GOTO neuroblastoma cells

The sugar chain structures of the cell surface change dramatically during cellular differentiation. A human neuroblastoma cell line, GOTO, is known to differentiate into neuronal cells and Schwannian cell-like cells on treatments with dibutyryl cAMP and bromodeoxyuridine, respectively. We have examined the expression of UDP-N-acetylglucosamine: beta-D-mannoside beta-1,4N-acetylglucosaminyltransferase III (GnT-III: EC 2.4.1.144) and UDP-N-acetylglucosamine: alpha-6-D-mannoside beta-1,6N-acetylglucosaminyltransferase V (GnT-V: EC 2.4.1.155), two major branch forming enzymes in N-glycan synthesis, in GOTO cells on two distinct directions of differentiation. In neuronal cell differentiation, GnT-III activity showed a slight increase during initial treatment with Bt2cAMP for 4 days and decreased drastically after the fourth day, but the mRNA level of GnT-III did not show a decrease but in fact a slight increase. GnT-V activity increased to approximately two- to three-fold the initial level with increasing mRNA level after 8 days, and lectin blot analysis showed an increase in reactivity to Datsura stramonium (DSA) of the immunoprecipitated neural cell adhesion molecule (NCAM). In Schwannian cell differentiation, the activity and mRNA level of GnT-III showed no significant change on treatment with BrdU. GnT-V activity also showed no change in spite of the gradual increase in the mRNA level. These results suggest that the activation of GnT-V during neuronal cell differentiation of GOTO cells might be a specific change for branch formation in N-glycans, and this affects the sugar chain structures of some glycoproteins such as NCAM.

cAMP increasing agents prevent the stimulation of heat-shock protein 70 (HSP70) gene expression by cadmium chloride in human myeloid cell lines

Treatment of U-937 human promonocytic cells with the cAMP increasing agents isoproterenol plus theophylline decreased the basal level of heat-shock protein 70 (HSP70) mRNA. In addition, the cAMP increasing agents attenuated the increase in HSP70 mRNA and protein levels produced by cadmium chloride in U-937 and other human myeloid cell lines, reduced the capacity of cadmium treatment to generate stress-tolerance, and attenuated the cadmium-produced stimulation of heat-shock factor (HSF) binding activity. By contrast, isoproterenol plus theophylline failed to attenuate the stimulation of HSP70 gene expression and HSF binding activity caused by heat-shock. Isoproterenol plus theophylline did not prevent the uptake of cadmium into the cells, and increased to a similar extent the intracellular cAMP levels in cadmium- and heat-treated cells. The cAMP increasing agents reduced the induction by cadmium of the HSP27 stress gene, but failed to attenuate other cadmium-elicited stress reactions such as the inhibition of total protein synthesis. It is concluded that cAMP does not inhibit the stress response as a whole, but it interferes with some step of the pathway by which cadmium specifically stimulates HSF binding activity and as a consequence HSP70 gene expression, in human myeloid cell lines.

Reversal of alcohol's effects on neurite extension and on neuronal GAP43/B50, N-myc, and c-myc protein levels by retinoic acid

Alcohol teratogenesis may be due in part to inhibition of neuronal differentiation by ethanol. We showed previously that alcohol decreased neuronal differentiation (neurite extension) and increased N-myc and c-myc neuronal protein levels. Since Growth-Associated Protein 43 (GAP43/B50) levels must increase for neurons to differentiate, alcohol may decrease GAP43/B50. Alcohol dose-dependently (0-0.5%) decreased GAP43/B50 protein levels by up to 92% in immature LA-N-5 cells. Five nM retinoic acid alone induced differentiation and increased GAP43/B50 levels to 230% of control. These retinoic acid-induced increases in GAP43/B50 and neurite outgrowth, and decreases in N-myc and c-myc, were reversed dose-dependently by alcohol (0-0.5%). Conversely, the adverse effects of 0.25% alcohol on neurite extension, GAP43/B50, N-myc, and c-myc were prevented by 15 and 45 nM retinoic acid. These results suggest that inhibition of neuronal differentiation by alcohol and prevention of such effects by retinoic acid are related to changes in GAP43/B50, N-myc and c-myc.

Expression of heat shock genes during differentiation of mammalian osteoblasts and promyelocytic leukemia cells

The progressive differentiation of both normal rat osteoblasts and HL-60 promyelocytic leukemia cells involves the sequential expression of specific genes encoding proteins that are characteristic of their respective developing cellular phenotypes. In addition to the selective expression of various phenotype marker genes, several members of the heat shock gene family exhibit differential expression throughout the developmental sequence of these two cell types. As determined by steady state mRNA levels, in both osteoblasts and HL-60 cells expression of hsp27, hsp60, hsp70, hsp89 alpha, and hsp89 beta may be associated with the modifications in gene expression and cellular architecture that occur during differentiation. In both differentiation systems, the expression of hsp27 mRNA shows a 2.5-fold increase with the down-regulation of proliferation while hsp60 mRNA levels are maximal during active proliferation and subsequently decline post-proliferatively. mRNA expression of two members of the hsp90 family decreases with the shutdown of proliferation, with a parallel relationship between hsp89 alpha mRNA levels and proliferation in osteoblasts and a delay in down-regulation of hsp89 alpha mRNA levels in HL-60 cells and of hsp89 beta mRNA in both systems. Hsp70 mRNA rapidly increases, almost twofold, as proliferation decreases in HL-60 cells but during osteoblast growth and differentiation was only minimally detectable and showed no significant changes. Although the presence of the various hsp mRNA species is maintained at some level throughout the developmental sequence of both osteoblasts and HL-60 cells, changes in the extent to which the heat shock genes are expressed occur primarily in association with the decline of proliferative activity. The observed differences in patterns of expression for the various heat shock genes are consistent with involvement in mediating a series of regulatory events functionally related to the control of both cell growth and differentiation.