ABSTRACT
BACKGROUND: The anti-epileptic drug valproic acid (VPA) has attracted attention as an anti-cancer agent. METHODS: The present study investigated effects of VPA exposure on histone deacetylase (HDAC) inhibition, cell growth, cell speed, and the degree of Erk1/2 phosphorylation in 10 cell lines (BT4C, BT4Cn, U87MG, N2a, PC12-E2, CSML0, CSML100, HeLa, L929, Swiss 3T3). RESULTS: VPA induced significant histone deacetylase (HDAC) inhibition in most of the cell lines, but the degree of inhibition was highly cell type-specific. Moreover, cell growth, motility and the degree of Erk1/2 phosphorylation were inhibited, activated, or unaffected by VPA in a cell type-specific manner. Importantly, no relationship was found between the effects of VPA on HDAC inhibition and changes in the degree of Erk1/2 phosphorylation, cell growth, or motility. In contrast, VPA-induced modulation of the MAPK pathway downstream of Ras but upstream of MEK (i.e., at the level of Raf) was important for changes in cell speed. CONCLUSIONS: These results suggest that VPA can modulate the degree of Erk1/2 phosphorylation in a manner unrelated to HDAC inhibition and emphasize that changes in the degree of Erk1/2 phosphorylation are also important for the anti-cancer properties of VPA.
Subject(s)
Cell Proliferation/drug effects , Enzyme Inhibitors/pharmacology , Histone Deacetylases/chemistry , Mitogen-Activated Protein Kinase 1/antagonists & inhibitors , Mitogen-Activated Protein Kinase 3/antagonists & inhibitors , Valproic Acid/pharmacology , Acetylation/drug effects , Animals , Blotting, Western , Cell Adhesion/drug effects , Cell Movement/drug effects , Cells, Cultured , Dose-Response Relationship, Drug , Histone Deacetylases/metabolism , Humans , Mice , Mitogen-Activated Protein Kinase 1/metabolism , Mitogen-Activated Protein Kinase 3/metabolism , Phosphorylation/drug effects , RatsSubject(s)
Adenosine Triphosphate/metabolism , Neural Cell Adhesion Molecules/metabolism , Adenosine Triphosphatases/metabolism , Adenosine Triphosphate/analogs & derivatives , Animals , Models, Molecular , Nervous System/metabolism , Neural Cell Adhesion Molecules/chemistry , Neural Cell Adhesion Molecules/genetics , Neurites/metabolism , Protein Conformation , Receptors, Fibroblast Growth Factor/chemistry , Receptors, Fibroblast Growth Factor/metabolism , Signal Transduction/physiologyABSTRACT
The neural cell adhesion molecule (NCAM) is involved in development of the nervous system, in brain plasticity associated with learning and memory, and in neuronal regeneration. NCAM regulates these processes by influencing cell adhesion, cell migration, and neurite outgrowth. NCAM activates intracellular signaling upon homophilic NCAM binding, and this is a prerequisite for NCAM-stimulated neurite outgrowth. NCAM is synthesized in three main membrane-bound isoforms, NCAM-120, NCAM-140, and NCAM-180. Soluble forms of NCAM in blood and cerebrospinal fluid have also been found, although the functional significance of these forms remains unclear. In this report, we demonstrate that NCAM can be released from primary hippocampal neurons in culture. The release was enhanced by application of ATP and inhibited by the metalloproteinase inhibitor BB-3103. ATP also induced metalloproteinase-dependent release of all three major NCAM isoforms from NCAM-transfected fibroblastoid L-cells. In this model system, the extracellular ATP-binding site of NCAM was shown not to be necessary for ATP-induced NCAM release. Furthermore, inhibition of serine, cysteine, and aspartic proteinases could not prevent ATP-induced down-regulation of NCAM in L-cells, suggesting that NCAM is cleaved directly by a metalloproteinase. Aggregation of hippocampal neurons in culture was increased in the presence of the metalloproteinase inhibitor GM 6001, consistent with a metalloproteinase-dependent shedding of NCAM occurring in these cells. Moreover, NCAM-dependent neurite outgrowth was significantly reduced by application of GM 6001. Taken together, these results suggest that membrane-bound NCAM can be cleaved extracellularly by a metalloproteinase and that metalloproteinase-dependent shedding of NCAM regulates NCAM-mediated neurite outgrowth.
Subject(s)
Metalloproteases/metabolism , Neural Cell Adhesion Molecules/metabolism , Neurons/metabolism , Adenosine Triphosphate/pharmacology , Animals , Cell Aggregation/drug effects , Cells, Cultured , Down-Regulation , Electrophoresis, Polyacrylamide Gel , Enzyme Inhibitors/pharmacology , Hippocampus/drug effects , Hippocampus/metabolism , Immunohistochemistry , Isoenzymes/drug effects , Isoenzymes/metabolism , Mice , Neural Cell Adhesion Molecules/drug effects , Neurons/drug effects , Polymerase Chain Reaction , Rats , TransfectionABSTRACT
The neural cell adhesion molecule (NCAM) promotes axonal outgrowth, presumably through an interaction with the fibroblast growth factor receptor (FGFR). NCAM also has a little-understood ATPase activity. We here demonstrate for the first time a direct interaction between NCAM (fibronectin type III [F3] modules 1 and 2) and FGFR1 (Ig modules 2 and 3) by surface plasmon resonance (SPR) analysis. The structure of the NCAM F3 module 2 was determined by NMR and the module was shown by NMR to interact with the FGFR1 Ig module 3 and ATP. The NCAM sites binding to FGFR and ATP were found to overlap and ATP was shown by SPR to inhibit the NCAM-FGFR binding, indicating that ATP probably regulates the NCAM-FGFR interaction. Furthermore, we demonstrate that the NCAM module was able to induce activation (phosphorylation) of FGFR and to stimulate neurite outgrowth. In contrast, ATP inhibited neurite outgrowth induced by the module.
Subject(s)
Adenosine Triphosphate/metabolism , Neural Cell Adhesion Molecules/chemistry , Neural Cell Adhesion Molecules/metabolism , Protein Structure, Secondary , Receptor Protein-Tyrosine Kinases/chemistry , Receptor Protein-Tyrosine Kinases/metabolism , Receptors, Fibroblast Growth Factor/chemistry , Receptors, Fibroblast Growth Factor/metabolism , Amino Acid Sequence , Animals , Cells, Cultured , Humans , Mice , Models, Molecular , Molecular Sequence Data , Nuclear Magnetic Resonance, Biomolecular , Peptides/chemistry , Peptides/metabolism , Protein Binding , Protein Structure, Tertiary , Rats , Receptor, Fibroblast Growth Factor, Type 1ABSTRACT
The neural cell adhesion molecule (NCAM) plays a key role in morphogenesis of the nervous system and in remodeling of neuronal connections accompanying regenerative and cognitive processes. Recently, a new synthetic ligand of NCAM, the C3-peptide, which binds to the NCAM IgI module, has been identified by means of combinatorial chemistry (Rønn, L. C. B, Olsen, M., Ostergaard, S., Kiselyov, V., Berezin, V., Mortensen, M. T., Lerche, M. H., Jensen, P. H., Soroka, V., Saffell, J. L., Doherty, P., Poulsen, F. M., Bock, E., Holm, A., and Saffells, J. L. (1999) Nat. Biotechnol. 17, 1000-1005). In vitro, the dendrimeric form of C3, termed C3d, disrupts NCAM-mediated cell adhesion, induces neurite outgrowth, and triggers intracellular signaling cascades similar to those activated by homophilic NCAM binding. The peptide may therefore be expected to regulate regeneration and synaptic plasticity. Here we demonstrate that in primary cultures of hippocampal neurons: 1) C3d induces a sustained neuritogenic response, the neuritogenic activity of the compound being dependent on the dose, starting time, and duration of peptide application; 2) the peptide triggers the neuritogenic response by forming an adhesive substratum necessary for NCAM-mediated neurite formation and elongation; 3) C3d promotes synapse formation; and 4) C3d modulates the presynaptic function, causing a transient increase of the function at low (2 and 5 microm) doses and a reduction when applied at a higher concentration (10 microm). The effect of the peptide is dependent on the activation of the fibroblast growth factor receptor. We suggest that C3d may constitute a useful lead for the development of compounds for treatment of various neurodegenerative disorders.
