miR-196a-2 Promotes Malignant Progression of Thyroid Carcinoma by Targeting NRXN1

Thyroid cancer (TC) is the most common endocrine malignant disease with a rising morbidity year by year. Accumulating studies have shown that microRNAs (miRNAs) play a regulatory role in the progression of various tumors, but the molecular regulatory mechanism of miR-196a-2 in TC is still unknown. qRT-PCR was employed to measure the expression of miR-196a-2 and NRXN1 mRNA in TC cells, while western blot was used to detect the protein expression of NRXN1. CCK-8, colony formation and flow cytometry assays were used to measure cell proliferation and apoptosis of TC cells. Dual-luciferase reporter gene assay was used to predict and verify the targeted binding relationship between miR-196a-2 and NRXN1. Our study results manifested that miR-196a-2 was dramatically overexpressed in cells of TC, while NRXN1 was lowly expressed. miR-196a-2 could promote cell proliferation and inhibit cell apoptosis of TC. Additionally, miR-196a-2 could also target and inhibit the expression of NRXN1. Silencing NRXN1 could reverse the inhibitory effect of miR-196a-2 downregulation on cell proliferation of TC, as well as the promoting effect on cell apoptosis. In a conclusion, we found that miR-196a-2 could promote cell proliferation and inhibit cell apoptosis of TC by targeting NRXN1. Therefore, miR-196a-2/NRXN1 is potential to be a molecular therapeutic target for TC.

Heparan Sulfate Organizes Neuronal Synapses through Neurexin Partnerships

Synapses are fundamental units of communication in the brain. The prototypical synapse-organizing complex neurexin-neuroligin mediates synapse development and function and is central to a shared genetic risk pathway in autism and schizophrenia. Neurexin's role in synapse development is thought to be mediated purely by its protein domains, but we reveal a requirement for a rare glycan modification. Mice lacking heparan sulfate (HS) on neurexin-1 show reduced survival, as well as structural and functional deficits at central synapses. HS directly binds postsynaptic partners neuroligins and LRRTMs, revealing a dual binding mode involving intrinsic glycan and protein domains for canonical synapse-organizing complexes. Neurexin HS chains also bind novel ligands, potentially expanding the neurexin interactome to hundreds of HS-binding proteins. Because HS structure is heterogeneous, our findings indicate an additional dimension to neurexin diversity, provide a molecular basis for fine-tuning synaptic function, and open therapeutic directions targeting glycan-binding motifs critical for brain development.

Morphogenetic Studies of the Drosophila DA1 Ventral Olfactory Projection Neuron

In the Drosophila olfactory system, odorant information is sensed by olfactory sensory neurons and relayed from the primary olfactory center, the antennal lobe (AL), to higher olfactory centers via olfactory projection neurons (PNs). A major portion of the AL is constituted with dendrites of four groups of PNs, anterodorsal PNs (adPNs), lateral PNs (lPNs), lateroventral PNs (lvPNs) and ventral PNs (vPNs). Previous studies have been focused on the development and function of adPNs and lPNs, while the investigation on those of lvPNs and vPNs received less attention. Here, we study the molecular and cellular mechanisms underlying the morphogenesis of a putative male-pheromone responding vPN, the DA1 vPN. Using an intersection strategy to remove background neurons labeled within a DA1 vPN-containing GAL4 line, we depicted morphological changes of the DA1 vPN that occurs at the pupal stage. We then conducted a pilot screen using RNA interference knock-down approach to identify cell surface molecules, including Down syndrome cell adhesion molecule 1 and Semaphorin-1a, that might play essential roles for the DA1 vPN morphogenesis. Taken together, by revealing molecular and cellular basis of the DA1 vPN morphogenesis, we should provide insights into future comprehension of how vPNs are assembled into the olfactory neural circuitry.

Specification of Dendritogenesis Site in Drosophila aCC Motoneuron by Membrane Enrichment of Pak1 through Dscam1

Precise positioning of dendritic branches is a critical step in the establishment of neuronal circuitry. However, there is limited knowledge on how environmental cues translate into dendrite initiation or branching at a specific position. Here, through a combination of mutation, RNAi, and imaging experiments, we found that a Dscam-Dock-Pak1 hierarchical interaction defines the stereotypical dendrite growth site in the Drosophila aCC motoneuron. This interaction localizes the Cdc42 effector Pak1 to the plasma membrane at the dendrite initiation site before the activation of Cdc42. Ectopic expression of membrane-anchored Pak1 overrides this spatial specification of dendritogenesis, confirming its function in guiding Cdc42 signaling. We further discovered that Dscam1 localization in aCC occurs through an inter-neuronal contact that involves Dscam1 in the partner MP1 neuron. These findings elucidate a mechanism by which Dscam1 controls neuronal morphogenesis through spatial regulation of Cdc42 signaling and, subsequently, cytoskeletal remodeling.

Mildronate as a regulator of protein expression in a rat model of Parkinson's disease

BACKGROUND

Mildronate (3-[2,2,2-trimethylhydrazinium] propionate dihydrate) traditionally is a well-known cardioprotective drug. However, our recent studies convincingly demonstrated its neuroprotective properties. The aim of the present study was to evaluate the influence of mildronate on the expression of proteins that are involved in the differentiation and survival of the nigrostriatal dopaminergic neurons in the rat model of Parkinson's disease (PD). The following biomarkers were used: heat shock protein 70 (Hsp70, a molecular chaperone), glial cell line-derived nerve growth factor (GDNF, a growth factor promoting neuronal differentiation, regeneration, and survival), and neural cell adhesion molecule (NCAM).

MATERIAL AND METHODS

PD was modeled by 6-hydroxydopamine (6-OHDA) unilateral intrastriatal injection in rats. Mildronate was administered at doses of 10, 20, and 50 mg/kg for 2 weeks intraperitoneally before 6-OHDA injection. Rat brains were dissected on day 28 after discontinuation of mildronate injections. The expression of biomarkers was assessed immunohistochemically and by western blot assay.

RESULTS

6-OHDA decreased the expression of Hsp70 and GDNF in the lesioned striatum and substantia nigra, whereas in mildronate-pretreated (20 and 50 mg/kg) rats, the expression of Hsp70 and GDNF was close to the control group values. NCAM expression also was decreased by 6-OHDA in the striatum and it was totally protected by mildronate at a dose of 50 mg/kg. In contrast, in the substantia nigra, 6-OHDA increased the expression of NCAM, while mildronate pretreatment (20 and 50 mg/kg) reversed the 6-OHDA-induced overexpression of NCAM close to the control values.

CONCLUSION

The obtained data showed that mildronate was capable to regulate the expression of proteins that play a role in the homeostasis of neuro-glial processes.

Identification of NCAM-binding peptides promoting neurite outgrowth via a heterotrimeric G-protein-coupled pathway

A combinatorial library of undecapeptides was produced and utilized for the isolation of peptide binding to the fibronectin type 3 modules (F3I-F3II) of the neural cell adhesion molecule (NCAM). The isolated peptides were sequenced and produced as dendrimers. Two of the peptides (denoted ENFIN2 and ENFIN11) were confirmed to bind to F3I-F3II of NCAM by surface plasmon resonance. The peptides induced neurite outgrowth in primary cerebellar neurons and PC12E2 cells, but had no apparent neuroprotective properties. NCAM is known to activate different intracellular pathways, including signaling through the fibroblast growth factor receptor, the Src-related non-receptor tyrosine kinase Fyn, and heterotrimeric G-proteins. Interestingly, neurite outgrowth stimulated by ENFIN2 and ENFIN11 was independent of signaling through fibroblast growth factor receptor and Fyn, but could be inhibited with pertussis toxin, an inhibitor of certain heterotrimeric G-proteins. Neurite outgrowth induced by trans-homophilic NCAM was unaffected by the peptides, whereas knockdown of NCAM completely abrogated ENFIN2- and ENFIN11-induced neuritogenesis. These observations suggest that ENFIN2 and ENFIN11 induce neurite outgrowth in an NCAM-dependent manner through G-protein-coupled signal transduction pathways. Thus, ENFIN2 and ENFIN11 may be valuable for exploring this particular type of NCAM-mediated signaling.

MuSK antibody positive myasthenia gravis plasma modifies MURF-1 expression in C2C12 cultures and mouse muscle in vivo

MG is an antibody-mediated disease that is often treated with corticosteroids. Antibodies to the muscle specific tyrosine kinase (MuSK) have been identified in a proportion of patients with myasthenia gravis (MG) without acetylcholine receptor (AChR) antibodies. MuSK-MG patients often suffer from marked facial muscle weakness, and some patients develop facial and tongue muscle atrophy. MuSK is a receptor tyrosine kinase that plays an essential role during development and is thought to play a trophic role in mature muscle. It is possible, therefore, that the muscle atrophy results from the action of the MuSK antibodies themselves, but effects of corticosteroids on muscle might also be involved. Muscle atrophy in vivo is associated with upregulation of striated Muscle RING-Finger protein-1 (MURF-1), and MURF-1 is also upregulated in C2C12 myotubes exposed to the corticosteroid, dexamethasone (Dex). Here we investigated the effects of MuSK antibodies or Dex on MURF-1 expression in C2C12 cultures and in mouse muscles after treatment in vivo, using quantitative Western blotting. We also looked at expression of neural cell adhesion molecule (NCAM, CD56) that is upregulated after denervation in vivo. MuSK-MG plasma and purified IgG from a patient with marked muscle atrophy modestly increased MURF-1 expression in C2C12 cells in culture, and MURF-1 expression in mouse masseter (facial) muscle, but not in gastrocnemius (leg). Dex had a more marked effect on MURF-1 expression in C2C12 cells, but did not affect MURF-1 expression in either muscle. However, both in C2C12 cells and in vivo, Dex substantially reduced NCAM expression. These results provide the first evidence that MuSK-MG plasma can influence expression of an atrophy-related protein, and preliminary evidence that a facial muscle, the masseter, is more susceptible to this effect. They indicate the need for further studies on muscle atrophy, MuSK-MG antibodies, the effects of steroids, and the intracellular pathways involved.

A peptide from the first fibronectin domain of NCAM acts as an inverse agonist and stimulates FGF receptor activation, neurite outgrowth and survival

Neural cell adhesion molecule (NCAM) contributes to axon growth and guidance during development and learning and memory in adulthood. Although the Ig domains mediate homophilic binding, outgrowth activity localizes to two membrane proximal fibronectin-like domains. The first of these contains a site identified as a potential FGF receptor (FGFR) activation motif (FRM) important for NCAM stimulation of neurite outgrowth, but its activity has hitherto remained hypothetical. Here, we have tested the effects of a domain-specific antibody and peptides corresponding to the FRM in cellular assays in vitro. The first fibronectin domain antibody inhibited NCAM-stimulated outgrowth, indicating the importance of the domain for NCAM function. Monomeric FRM peptide behaved as an inverse agonist; low concentrations specifically inhibited neurite outgrowth stimulated by NCAM and cellular responses to FGF2, while saturating concentrations stimulated FGFR-dependent neurite outgrowth equivalent to NCAM itself. Dendrimeric FRM peptide was 125-fold more active and stimulated FGFR activation, FGFR-dependent and FGF-mimetic neurite outgrowth and cell survival (but not proliferation). We conclude that the FRM peptide contains NCAM-mimetic bioactivity accounted for by stimulation of FGF signalling pathways at the level of or upstream from FGF receptors, and discuss the possibility that FRM comprises part of an FGFR activation site on NCAM.

Neural Cell Adhesion Molecule Contributes to Hemopoiesis-Supporting Capacity of Stromal Cell Lines

To clarify mechanisms underlying cell-to-cell interactions between hemopoietic stem cells (HSCs) and stromal cells, we established a stromal cell line (FMS/PA6-P) from day-16 fetal bone marrow (BM) adherent cells using an anti-PA6 monoclonal antibody (mAb) specific for BM stromal cells. Importantly, this FMS/PA6-P cell line, showing homogenous fibroblastic morphology, is absent from hematolymphoid and endothelial lineage markers and maintains a high level of expression of PA6 molecule, recognized by the anti-PA6 mAb, for approximately 20 passages. Further, the cell line expressing a high level of PA6 molecule has a better hemopoiesis-supporting capacity in vitro than other stromal cell lines such as PA6 and MS-5. In fact, the PA6 molecule is closely related to the hemopoiesis-supporting capacity of the stromal cells because the proliferation of HSCs was suppressed to a great extent by the anti-PA6 mAb. Affinity chromatography and mass peptide fingerprinting revealed that the protein reacting with the anti-PA6 mAb is neural cell adhesion molecule (NCAM). The frequencies of long-term cobblestone area-forming cells and long-term culture-initiating cells were significantly suppressed by repression of NCAM in the FMS/PA6-P cells using NCAM small interfering RNA. Our findings clearly indicate that NCAM functions on the maintenance of HSCs.

Reduced neuronal expression of synaptic transmission modulator HNK-1/neural cell adhesion molecule as a potential consequence of amyloid beta-mediated oxidative stress: a proteomic approach

Abstract Oxidative stress imparted by reactive oxygen species (ROS) is implicated in the pathogenesis of Alzheimer's disease (AD). Given that amyloid beta (Abeta) itself generates ROS that can directly damage proteins, elucidating the functional consequences of protein oxidation can enhance our understanding of the process of Abeta-mediated neurodegeneration. In this study, we employed a biocytin hydrazide/streptavidin affinity purification methodology followed by two-dimensional liquid chromatography tandem mass spectrometry coupled with SEQUEST bioinformatics technology, to identify the targets of Abeta-induced oxidative stress in cultured primary cortical mouse neurons. The Golgi-resident enzyme glucuronyltransferase (GlcAT-P) was a carbonylated target that we investigated further owing to its involvement in the biosynthesis of HNK-1, a carbohydrate epitope expressed on cell adhesion molecules and implicated in modulating the effectiveness of synaptic transmission in the brain. We found that increasing amounts of Abeta, added exogenously to the culture media of primary cortical neurons, significantly decreased HNK-1 expression. Moreover, in vivo, HNK-1 immunoreactivity was decreased in brain tissue of a transgenic mouse model of AD. We conclude that a potential consequence of Abeta-mediated oxidation of GlcAT-P is impairment of its enzymatic function, thereby disrupting HNK-1 biosynthesis and possibly adversely affecting synaptic plasticity. Considering that AD is partly characterized by progressive memory impairment and disordered cognitive function, the data from our in vitro studies can be reconciled with results from in vivo studies that have demonstrated that HNK-1 modulates synaptic plasticity and is critically involved in memory consolidation.

mu-Opioid receptor gene expression: the role of NCAM

We have investigated the mechanisms regulating the expression of the mu-opioid receptor, using P19 mouse embryonal carcinoma cells, which normally lack this receptor, but which can be induced to express it in aggregated cells by retinoic acid treatment. The expression level of mu-opioid receptor mRNA was found to be closely correlated with aggregation status, and more specifically by cell to cell interaction requiring neural cell adhesion molecules (NCAM). We showed that NCAM activates the mu-opioid receptor gene through a pathway involving phospholipase C-arachidonic acid-calcium channel-calcium/calmodulin kinase II. A similar pathway was previously shown to promote neurite outgrowth, however, with distinct specificity, including the role of calcium channels. Activation of L-type calcium channels elevated mu-opioid receptor expression, while N-type-channel activity had the opposite effect. The effect of anti-NCAM-antibody treatment was not due to retardation of general neural development and was specific to the mu-opioid receptor gene. Our results indicate that the P19 system is an useful model to study the expression of the mu-opioid receptor gene.

The adhesion molecule TAG-1 mediates the migration of cortical interneurons from the ganglionic eminence along the corticofugal fiber system

Cortical nonpyramidal cells, the GABA-containing interneurons, originate mostly in the medial ganglionic eminence of the ventral telencephalon and follow tangential migratory routes to reach the dorsal telencephalon. Although several genes that play a role in this migration have been identified, the underlying cellular and molecular cues are not fully understood. We provide evidence that the neural cell adhesion molecule TAG-1 mediates the migration of cortical interneurons. We show that the migration of these neurons occurs along the TAG-1-expressing axons of the developing corticofugal system. The spatial and temporal pattern of expression of TAG-1 on corticofugal fibers coincides with the order of appearance of GABAergic cells in the developing cortex. Blocking the function of TAG-1, but not of L1, another adhesion molecule and binding partner of TAG-1, results in a marked reduction of GABAergic neurons in the cortex. These observations reveal a mechanism by which the adhesion molecule TAG-1, known to be involved in axonal pathfinding, also takes part in neuronal migration.

Ectodomain shedding of L1 adhesion molecule promotes cell migration by autocrine binding to integrins

The L1 adhesion molecule plays an important role in axon guidance and cell migration in the nervous system. L1 is also expressed by many human carcinomas. In addition to cell surface expression, the L1 ectodomain can be released by a metalloproteinase, but the biological function of this process is unknown. Here we demonstrate that membrane-proximal cleavage of L1 can be detected in tumors and in the developing mouse brain. The shedding of L1 involved a disintegrin and metalloproteinase (ADAM)10, as transfection with dominant-negative ADAM10 completely abolishes L1 release. L1-transfected CHO cells (L1-CHO) showed enhanced haptotactic migration on fibronectin and laminin, which was blocked by antibodies to alpha v beta 5 and L1. Migration of L1-CHO cells, but not the basal migration of CHO cells, was blocked by a metalloproteinase inhibitor, indicating a role for L1 shedding in the migration process. CHO and metalloproteinase-inhibited L1-CHO cells were stimulated to migrate by soluble L1-Fc protein. The induction of migration was blocked by alpha v beta 5-specific antibodies and required Arg-Gly-Asp sites in L1. A 150-kD L1 fragment released by plasmin could also stimulate CHO cell migration. We propose that ectodomain-released L1 promotes migration by autocrine/paracrine stimulation via alpha v beta 5. This regulatory loop could be relevant for migratory processes under physiological and pathophysiological conditions.

L1 cell adhesion molecule signal cascades: targets for ethanol developmental neurotoxicity

A major mechanism guiding neural development is through cell-cell and cell-matrix adhesions and signaling mediated by cell adhesion molecules (CAMs). The majority of CAMs have been grouped into three families: the cadherins, the integrins and the members of the immunoglobulin superfamily including L1. While the elucidation of new receptors and matrix components has become a frequent occurrence, the elucidation of the mechanisms by which they operate, and the function of those mechanisms in complex developmental events remains rudimentary. Members of all three families participate in differential adhesion, signal transduction and physical/mechanical effects. Each of these modes of action is a potential target for developmental neurotoxicants. In this brief review, the role of L1 in normal and abnormal neurodevelopment will be summarized. L1 is a cell surface transmembrane glycoprotein with a single copy gene on the X chromosome. There are two alternatively spliced exons, with the RSLE containing form found only on axons and growth cones of post-mitotic neurons. L1 mediates the following functions: adhesion, neurite extension, neuronal migration, and axon fasciculation. L1 is critical for normal neural development; humans with genetic defects in L1, termed corpus callosum hypoplasia, mental retardation, adducted thumbs, spasticity and hydrocephalus (CRASH) syndrome, and mice lacking expression of L1 have extensive neuropathologic and aberrant behaviors. The observation that patients with fetal alcohol syndrome share similar features to patients with CRASH has lead to the investigation of the effects of ethanol on L1. Physiologic concentrations of ethanol have been shown to inhibit L1 mediated neurite outgrowth in cerebellar granule neurons. Such inhibition may result from decreased expression, altered cell surface distribution, impaired signal transduction, or impaired interaction with the cytoskeleton. These data indicate that L1 and its associated signaling pathways are potentially targets for developmental neurotoxicants.

Soluble interleukin-6 receptor alpha inhibits the cytokine-Induced fractalkine/CX3CL1 expression in human vascular endothelial cells in culture

Soluble form of IL-6 receptor alpha (sIL-6R) is known to serve as an agonist, without exogenous IL-6, on endothelial cells which do not express IL-6R but have only IL-6 receptor beta chain, gp130. We investigated the effect of sIL-6R on fractalkine expression in human umbilical vein endothelial cells (HUVECs) in culture. sIL-6R markedly inhibited HUVEC fractalkine/CX3CL1 expression induced by interleukin (IL)-1alpha, tumor necrosis factor (TNF)-alpha, or interferon (IFN)-gamma. IL-1alpha-induced fractalkine expression was inhibited by sIL-6R in time- and concentration-dependent manners. The experiment using actinomycin D indicated that sIL-6R lowered the stability of fractalkine mRNA. The inhibitory effect of sIL-6R was reversed by anti-gp130 neutralizing antibody. sIL-6R inhibited adhesion of mononuclear cells (MNCs) to HUVEC monolayers stimulated with IFN-gamma, but it did not inhibit the adhesion to monolayers stimulated with IL-1alpha. MNC chemotactic activity of conditioned medium of HUVEC stimulated with IL-1alpha or IFN-gamma was inhibited by co-treatment with sIL-6R. sIL-6R may play a regulatory role in immune responses by modulating the interaction between leukocytes and the vascular endothelium.

The highly sialylated isoform of the neural cell adhesion molecule is required for estradiol-induced morphological synaptic plasticity in the adult arcuate nucleus

The large quantities of polysialic acid (PSA) characterizing highly sialylated isoform of the neural cell adhesion molecule (PSA-NCAM), greatly reduce cell adhesion and render this particular cell surface adhesion molecule a likely candidate to intervene in dynamic neuronal phenomena, such as synaptic plasticity. The hypothalamic arcuate nucleus expresses high levels of PSA-NCAM and maintains a high capacity for neuroplastic changes in the adult. Thus, in the arcuate nucleus of female rats, varying circulating levels of estrogen give rise to a reversible reduction in the number of axo-somatic GABA synapses, together with a changing ensheathing of neuronal somata by astrocytes. To examine the role of PSA in such changes, we perturbed its expression, either by blockade with antibodies raised against this carbohydrate moiety (delivered intracerebroventricularly), or by its enzymatic cleavage after microinjection of endoneuraminidase N over the arcuate nucleus. Either procedure was performed in ovariectomized adult rats that received concurrent treatment with 17 beta-estradiol. Morphological synaptic plasticity was analysed using the unbiased disector method to assess synaptic densities in ultrathin sections of the arcuate nucleus immunogold-labelled for GABA. As expected, 17 beta-estradiol induced a significant reduction in the number of GABAergic axo-somatic synapses, a reduction which did not occur after infusion of anti-PSA antibodies or in vivo enzymatic removal of PSA from NCAM. Taken together, our results provide strong evidence that the presence of large quantities of the PSA moiety on NCAM is a necessary prerequisite for estrogen-induced phasic remodelling of synapses in the adult female arcuate nucleus.

Zinc-reversible antimicrobial activity of recombinant calprotectin (migration inhibitory factor-related proteins 8 and 14)

Recombinant calprotectin, consisting of 2 individual peptide chains also called migration inhibitory factor-related protein (MRP)-8 and MRP14, was tested for antimicrobial activity in a Candida albicans growth inhibition assay. Both chains contain HEXXH zinc-binding sites and might be expected to manifest zinc-reversible, antimicrobial activity similar to that of native calprotectin. When tested alone, neither MRP8 nor MRP14 showed activity in the Candida growth assay. A synthetic 20-amino acid peptide containing the HEXXH sequence of MRP14, along with a nearby HHH sequence, was also inactive in this assay. However, equimolar concentrations of MRP8 and MRP14 demonstrated a potent growth inhibitory effect that was reversible by 30 microM zinc. Truncated MRP14 (missing the C-terminal GHHHKPGLGEGTP tail) used in combination with MRP8 demonstrated zinc-reversible activity that was somewhat less than that with complete MRP14. These results suggest that intact calprotectin, consisting of a heterodimer of MRP8 and MRP14, is necessary to form a zinc-binding site capable of inhibiting microbial growth.